FOUS11 KWBC 031954
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 PM EST Mon Feb 3 2025

Valid 00Z Tue Feb 04 2025 - 00Z Fri Feb 07 2025

...Western U.S. across the Northern Rockies...=20
Days 1-3...

...Atmospheric River (AR) and upper low to sustain prolonged heavy
snow from Oregon/California border and Sierra Nevada to the=20
Northern Plains through Wednesday...

A positively-tilted upper-low off the Pacific NW coast trapped=20
beneath a strong upper ridge over Alaska is responsible for an=20
active jet stream pattern that is resulting in a highly active
storm track to open the month of February. The 200mb jet stream
pattern today sets the diffluent right-entrance region over
interior Northwest with a strong 1040mb+ high located over
southwest Canada (NAEFS shows the dome of high pressure tops the
97.5 climatological percentile over North Dakota by Tuesday AM).
This expansive area of high pressure will work to lock a cold
Canadian air-mass in place along and east of the Continental
Divide, while also causing easterly upslope flow to enhance
precipitation rates along the leeward-facing slopes of the Northern
Rockies. In tandem with the busy Pacific jet stream pattern, which
will deliver wave after wave of IVT surges into the western U.S.,
periods of heavy mountain snow will common from the West Coast=20
ranges (Sierra Nevada, OR/CA coastal ranges) on east to the=20
Sawtooth, Bear River, Bitterroot, Teton, Absaroka, Wind River, and=20
Lewis Ranges.

In terms of the time line, a stream of precipitation associated=20
with low pressure in the Great Basin is tied to period of mountain
snow this afternoon from the northern Sierra Nevada on north and=20
east to the Northern Plains. By Tuesday morning, the next wave of=20
low pressure approaches the CA coast with IVT values topping the=20
99.5 climatological percentile over the Sierra Nevada by Tuesday=20
afternoon. Strong WAA will keep the heaviest snowfall in the=20
Trinity/Shasta and northern Sierra NEvada to elevations >6,000ft,=20
while in the central and southern Sierra Nevada, snowfall will be=20
heaviest at elevations >7,000ft Tuesday afternoon and through=20
Tuesday evening. This same stream of moisture will keep heavy snow=20
in the forecast in parts of southeast OR, the Blue Mountains, and=20
both the Sawtooth and Bitterroots through Tuesday night. By=20
Wednesday morning, heavy snow will be common in the Teton and Wind
River Ranges. A brief reprieve in the heavy snowfall (sans some=20
ongoing upslope flow into the Cascades, Olympics, and coastal=20
ranges along the Pacific NW coast) will arrive Wednesday afternoon=20
and linger into Wednesday night, but the next Pacific storm system=20
arrives on Thursday with colder 700mb temps over northern CA this=20
time around per NAEFS. This should allow for heavier snowfall to=20
occur at lower elevations throughout the northern California=20
(excluding elevations <3,000ft) with some light snow accumulations=20
as low as 1,000ft western OR.

Through Thursday afternoon, WPC probabilities paint a very wintry
picture for much of the northwestern U.S.. Snow will be measured in
feet from the Sierra Nevada >7,000ft and the Trinity/Shasta/Salmon
mountains of northern CA >5,000ft through the Sawtooth, Bitterroots,
Absaroka, Tetons, and Wind River Ranges. The Sierra Nevada,=20
Sawtooth, and Tetons in particular could are forecast to see as=20
much as 3-5 feet of snowfall through Thursday. For western OR/WA,=20
parts of the Cascades, Olympics, and coastal ranges could see up to
a foot of snow with even light accumulations possible along the=20
I-5 corridor from the Willamette Valley on north through the=20
Seattle metro area. In fact, WPC probabilities through Tuesday=20
afternoon show low chances (10-30%) for snowfall >2" from the=20
Olympia on south to just north of the Columbia River. In the=20
Northern Plains, WPC probabilities show high chances (70-90%) for=20

4" of snowfall for areas east of the Lewis Range and surrounding=20

the Big Snowy/Little Belt mountains on east through northwest=20
North Dakota. In fact, these area event show low-to-moderate=20
chances (30-50%) for snowfall amounts >8". The WSSI shows the worst
impacts (Extreme Impacts mostly due to Snow Amount and Snow Load))
for the Sierra Nevada above 7,000ft. These areas are likely to=20
contend with dangerous to even impossible travel conditions, as=20
well as extensive closures and disruptions. Major Impacts=20
(considerable disruptions and dangerous travel conditions) are=20
highlighted in the Sawtooth, the Trinity/Shasta/Salmon of northern=20
CA and southern OR, and even some isolated areas of the OR coastal=20
ranges. Lastly, Moderate Impacts (hazardous driving conditions) are
most common in these areas lower elevated areas (still generally=20
above 2,000ft) from northern CA and the WA/OR coastal ranges=20
through southeast OR and into the northern Rockies.=20

Mullinax


...Northeast and Upper Great Lakes...=20

Day 1...

Persistent zonal flow regime will continue through D1 with an
analyzed speed max over the Great Lakes this afternoon pushing=20
eastward toward New England within the west to east aligned flow.

Over Upstate New York and New England, this jet presence upstream=20
over the Great Lakes will shift focus into the interior Northeast=20
with increasing ascent generally aligned over areas downwind of=20
Lake Ontario within the Tug Hill and Adirondacks, eventually=20
encompassing Northern New England with the greatest impacts in-of=20
the Green and White Mountains of VT/NH. The strongest signal for=20
heavy snow is within the Adirondacks and adjacent North Country=20
with probs for >4" upwards of 70-90% within those zones. Snow=20
levels across New England will be sufficient for snowfall above=20
1000', however greater impacts will be mainly relegated to zones=20
above 2000' with a strong gradient in the snow probability fields=20
for >4" with <20% in those lower elevations with a solid 50-80%=20
within the highest elevations of the Green and White Mountains.=20


...Upper Midwest...
Days 2-3...

Disturbance originating upstream across the Northern and Central=20
Rockies will eject eastward by midweek within a very progressive=20
upper flow evolution. Northern wave over WY/MT will progress east-=20
northeast across the Northern Plains and Upper Midwest with=20
snowfall breaking out downstream within a increasingly diffluent=20
mid-level pattern. Light to moderate snow will transpire over=20
north-central MT, far northern ND, and into northern MN with the=20
greatest impactful snowfall likely to occur over the Arrowhead of=20
MN. Modest probabilities (30-50%) of >4" exist from north- central=20
MT on D2 and passes just north of the ND-Canada border before=20
expanding into the Arrowhead of MN.


...Midwest to Mid-Atlantic...
Days 2-3...

System referenced in the section above will motion more west to=20
east across the Plains into the Ohio Valley and Mid Atlantic by the
late-D2 into much of D3. High pressure over the Great Lakes will=20
shift eastward into the Northeast U.S by Wednesday night with cold
air funneling south into the Mid Atlantic and guidance signaling a
classic CAD wedge pattern initiating east of the Appalachian=20
front. Limited blocking downstream over the North Atlantic will=20
preclude any chance for the high pressure to hang on across the=20
region with the continued eastward progression of the surface ridge
eventually shifting off the Atlantic seaboard. Despite its=20
positioning, time frame of interest for precipitation across the=20
Ohio Valley and Northeast will be occurring after peak diurnal=20
heating with wet bulb temperatures into the upper 20s and low 30s=20
by the time precipitation breaks out across areas of IN/OH over=20
into the Central Mid-Atlantic. Primary concern with the pattern is=20
the low to mid-level WAA regime as the surface reflection=20
encroaches from the west leading to a mixed ptype likely=20
correlating to more icy (IP/ZR) hydrometeors compared to plain snow
that we will see for points well to the north. Recent trends=20
within deterministic have been for colder wedge to hang on more=20
thoroughly for places east of the Apps. This colder trend is=20
partly in response to greater confluence downstream across the Gulf
of Maine. The highest ice probs located in- of the Laurel=20
Highlands of PA, western MD, and the WV Panhandle due to elevation
factors leaning colder at precip onset, as well as a secondary but
weaker ice maxima over the northern Ohio Valley where cold air=20
will be able to hang on through much of the event given stronger=20
WAA pattern displaced further downstream into the Mid- Atlantic=20 comparatively.=20

Ice probs of >0.1" are very high (80+%) across west-central PA=20
with the focus in-of the Laurel Highlands where even some modest
30-60% probs for >0.25" of ice accretion are forecast as of the=20
latest WWD progs. Northern Ohio Valley doesn't carry the=20
probabilistic maxima for >0.25" like the mountains to the east,=20
however >0.1" ice accretion is sufficiently within the 50-80%=20
range, very much a non-trivial depiction that will have to be=20
monitored closely. Ice probabilities also exist within the Central
Mid Atlantic east of the Blue Ridge, however a similar prob of=20
50-70% for >0.1" of ice exists for locations northwest of the fall
line across MD extending into southern PA with lower, non-zero=20
probs further east into the I-95 corridor and adjacent lowlands.=20
Setup is delicate with multiple variables involved including depth=20
of cold air, strength of LLJ providing WAA pattern, as well as=20
timing of precip onset. These factors will determine the magnitude=20
of ice potential in-of the Mid-Atlantic and Ohio Valley with=20
guidance starting to hone in on specifics as we move closer to the=20
event. While there may be some snow at onset across the Mid-
Atlantic on Wednesday and throughout the Interior Northeast and New
England as WAA increases on D3, probabilities for >4" remains low
and confined to parts of VT and ME.

Given the relatively large geographic coverage of at least 0.10"=20
ice potential and the increasing chances for over 0.25" of ice=20
accretion in parts of WV, MD, and PA... Key Messages have been=20
initiated for this event.

Kleebauer/Snell


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!76BKJeK4WDZz8dhcSrSdtbYfnXFwGLJx2JenAkneZ5sUX= Rl-uSZVW7Vs20Evp249u0dna6xfOcz8r1HLrQDUphRKLNo$=20

$$

=3D =3D =3D
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FOUS11 KWBC 040859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 AM EST Tue Feb 4 2025

Valid 12Z Tue Feb 04 2025 - 12Z Fri Feb 07 2025

...Western U.S. across the Northern Rockies...=20
Days 1-3...

...Atmospheric River (AR) and upper low maintain heavy snow from=20 Oregon/California border through the Northern Rockies and down the
Sierra Nevada through tonight. A separate low tracks through
California Thursday night bringing further heavy snow for the
Sierra Nevada...

A positively-tilted trough around an upper low off Vancouver Island
will continue to drift southwest off Pacific NW beneath a strong=20
upper ridge over Alaska through Wednesday before weakening in place
through Thursday. A zonal jet streak exceeding 130kt punches
through north-central CA today with the increasingly diffluent=20
left exit region over northern CA/NV today and across the=20
northern Great Basin/Rockies tonight. This will maintain the swath
of heavy snow over far northern CA into southern OR and northeast
through the Bitterroots. Day 1 snow probs for additional >18" are
40-70% for the Klamath/Siskiyou, Sawtooth/Salmon River and
Bitterroots with 70-90% probs for the Sierra Nevada above 6500ft.=20=20
A strong 1042mb high centered over the Canadian Prairies will=20
maintain the cold air on easterly upslope flow to enhance snow=20
rates along the leeward slopes of the Montana Rockies where Day 1
probs for >4" are 30-60%.

Low pressure ahead of the jet streak reaches the CA coast this
afternoon and northern NV tonight, bringing heavy precip to the
Sierra Nevada. Strong WAA with the low will keep snow levels=20
6000-7000ft. Heavy snow crosses the Teton and Wind River Ranges=20
late tonight into Wednesday.=20
Onshore flow will cause moderate snow over the Cascades and=20
coastal ranges Wednesday (where Day 2 snow probs for >8" are=20
50-80%) while the rest the Northwest enjoys a reprieve in snow.=20
However, the next Pacific storm system arrives Thursday with lower
heights and snow levels 3000-5000ft over northern CA Heavy snow=20
with prolonged 1-2"/hr rates is expected along the length of the=20
Sierra Nevada Thursday afternoon through the night. Day 3 snow
probs for >18" are 50-80%.


...Upper Midwest/Great Lakes...=20
Days 2-3...

Reinforcing shortwave trough that crosses OR tonight on the nose=20
of a powerful zonal jet will track over the northern Great Plains
Wednesday night. Warm air advection ahead of the wave allows=20
snowfall to breakout Wednesday afternoon over central MN, expanding
over northern MN/WI through the evening before tracking over the
U.P. into Thursday. Day 2.5 snow probs for >4" are 20-50%, highest
over the MN Arrowhead.

Jackson


...Midwest to Mid-Atlantic...
Days 2-3...

Very progressive shortwave ejecting eastward off the Pacific will=20
make quick headway to the east crossing the Continental Divide by=20
Wednesday morning with sights downstream on the Ohio Valley and=20
Mid-Atlantic by the end of D2. Further downstream, high pressure=20
will usher eastward out of the Great Lakes with a cold front=20
progression through the Mid- Atlantic and Northeast, solidifying a=20 relatively formidable polar airmass with a classic CAD wedge=20
situated east of the Appalachian front by Wednesday morning.=20
Consensus of forecast soundings across the region signal a shallow,
yet firmly entrenched airmass by Wednesday afternoon with a modest
CAA regime ongoing until later that evening. Limited blocking=20
across the North Atlantic will allow the surface ridge to propagate
eastward fairly quickly leading to a shift to modest return flow=20
by the very end of the D2 period allowing for warmer air to=20
protrude the boundary layer from south to north. This is important=20
as the approach of the aforementioned trough will couple with the=20
surface high off the Atlantic seaboard creating a modifying low to=20
mid- level airmass as the two work in tandem.

There's a growing consensus within the 00z deterministic suite for
a bout of mixed precipitation developing downstream across the=20
Ohio Valley and Mid-Atlantic within the increasing mid-level=20
difluence pattern ahead of the mean trough. Smaller shortwave=20
perturbations will also eject out ahead of the trough axis which=20
could spawn some scattered light precip ahead of the main QPF axis=20
that will approach more during the overnight time frame on=20
Wednesday night into early Thursday morning. The initial ptype may=20
start as a very brief period of snow for places further northeast=20
away from the nose of the budding 85H LLJ (50-55kts) initiating=20
over the Shenandoah. Any snowfall will quickly transition over to=20
sleet and/or freezing rain/drizzle before the main swath of precip=20
makes its way through the Appalachian and Allegheny front into the=20
rest of the Mid- Atlantic.

=46rom here, the approach of the shortwave trough will create a=20 strengthening v-vector component of the wind field allowing for=20
enhanced meridional flow capable of advecting much warmer air=20
poleward within the 925-650mb layer as indicated via bufr soundings
from locations across the Mid- Atlantic. Further west over the=20
Appalachian front extending from northern WV up through the Laurel=20 Highlands, a very shallow yet stern surface cold air pattern will=20
lock in and become very difficult to erode despite the increasing=20
warm air depth being advected overhead. The main thermodynamic=20
process for warming will likely have to come from latent heat=20
release of ice accretion processes to slowly maneuver the=20
temperature to near freezing by the end of the D2 window when much=20
of the precipitation will be shutting off. Wet bulb temps in the=20
higher elevations and elevated valleys west of the Blue Ridge will=20
likely be within 24-27F creating a large gap for any latent heat=20
processes to effectively kick the shallow cold layer out of the=20
lowest portions of the PBL. This is one of the main reasons this=20
area is the focus for the most significant ice accumulation=20
forecasts thus far with agreement among much of the deterministic=20
suite and national blend. Areas east of the Blue Ridge will likely=20
see the surface pattern erode a bit faster, especially those east=20
of the fall line within the Piedmont. Places between the Blue Ridge
and the fall line will be slower to erode as is customary within=20
these synoptic scale evolutions, especially when you factor in the=20
fresh CAA pattern that transpired less than 24 hrs before.=20

Ice probs of >0.1" remain very high (80+%) across west-central PA=20
with the focus in-of the Laurel Highlands where now 50-70% probs=20
for >0.25" of ice accretion are now forecast as of the latest WWD=20
progs. Northern Ohio Valley doesn't carry the probabilistic maxima=20
for >0.25" like the mountains to the east, however >0.1" ice=20
accretion is sufficiently within the 50-80% range, very much a non-
trivial depiction that has been consistent within NWP outputs. Ice probabilities also exist within the Central Mid Atlantic east of=20
the Blue Ridge with a similar prob of 50-70% for >0.1" of ice=20
existing for locations northwest of the fall line across MD=20
extending into southern PA. Newest WWD progs have introduced small=20
areas in-of the higher terrain of north-central MD within the Parrs
Ridge and Catoctin Mtn domains. These areas also have=20
probabilities for >0.25" now upwards of 30-40% for the event,=20
something we'll have to monitor closely as we move closer to the=20
event. Lower non-zero probs (20- 50%) exist for totals >0.1"=20
further east into the I-95 corridor and adjacent lowlands. Setup is
delicate with multiple variables involved including depth of cold=20
air, strength of LLJ providing WAA pattern, as well as timing of=20
precip onset. These factors will determine the magnitude of ice=20
potential in-of the Mid-Atlantic and Ohio Valley with guidance=20
starting to hone in on specifics as we move closer to the event.=20
While there may be some snow at onset across the Mid-Atlantic on=20
Wednesday and throughout the Interior Northeast and New England as=20
WAA increases on D3, probabilities for >4" remains low (10-40%) and
confined to mainly higher elevations of NY, VT, NH and ME.

Given the relatively large geographic coverage of at least 0.10"=20
ice potential and the increasing chances for over 0.25" of ice=20
accretion in parts of WV, MD, and PA... Key Messages continue for=20
this event.

Kleebauer



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!55ZGO0kmXlJMSOLOdySuP5k5U9km6UPbTmZ4wOEja5ADf= _PR_mVVma02h8M9SV2dBtxRuD6lr4WJvAgzyiBLP_f_wnk$=20

$$

=3D =3D =3D
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FOUS11 KWBC 041927
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 PM EST Tue Feb 4 2025

Valid 00Z Wed Feb 05 2025 - 00Z Sat Feb 08 2025

...Pacific Coast to the Northern Rockies...=20
Days 1-3...

An active period of weather will bring repeating rounds of active
wintry weather to much of the west, as a series of Atmospheric
Rivers (ARs) and varying snow levels occur through the week.

The forecast period begins with an impressive closed low
positioned just west of the WA/B.C. coast. 500mb height anomalies
within this low are progged by NAEFS to fall below the lowest ever
recorded in the CFSR climatology offshore these states by Wednesday
morning, indicating the intensity of this feature. In response,
downstream ascent will be impressive through mid-level divergence
and an intensifying jet streak exceeding 140kts Wednesday pivoting
into central CA. The overlap of this jet streak with confluent
mid-level flow downstream of the closed low will surge moisture
into the West as an AR, with both GEFS and ECENS probabilities
indicating a high risk (>90% chance) for 500 kg/m/s IVT lifting
into northern CA. With impressive mid and upper level winds
driving this AR, spillover moisture could also be significant,
aided by a wave of low pressure shifting east towards the Northern
Rockies beneath a spoke of vorticity shedding from the main low.
This will help spread an axis of moderate to heavy snowfall from
central CA through the northern Great Basin and into the Northern
Rockies D1. WPC probabilities are high (>70%) for more than 6
inches along the Sierra, across much of the northern CA ranges
including the coastal range, across the Blue Mountains, much of the
Northern Rockies, and into the Wind Rivers/Tetons. As much as 4-6
feet of snow is possible in the Sierra, with 1-2 feet possible in
the higher terrain of the other ranges. Additionally, with snow
levels crashing to the surface, lowland snow and coastal range snow
will also be impactful in Oregon.

The wave of low pressure D1 will push a cold front eastward behind
it, which when combined with the approach of the upper low will
lower heights and steepen lapse rates considerably late D1 and into=20
D2. This will result in snow levels falling to less than 500 ft as=20
far south as central Oregon, which when combined with the steep=20
lapse rates (dry adiabatic through the mid-levels as reflected by=20
regional forecast soundings) and increasing synoptic ascent, could=20
result in heavy snow into the coastal ranges and even the lowlands=20
of WA/OR and northern CA. Available moisture with this second wave=20
is somewhat suppressed from the prior day, but should still support
rounds of moderate to heavy precipitation falling as snow. There=20
is a lot of uncertainty involving the snowfall amounts due to the=20
likelihood for more periodic rounds of snow rather than a=20
continuous plume of precipitation, but theta-e lapse rates AOB=20
0C/Km will support convective rates which could quickly and=20
efficiently cause snowfall accumulations. Despite the transient=20
nature of heavy snow showers, WPC probabilities across the lowlands
of OR and southern WA, as well as some of the lower elevations of=20
northern CA reach 50-70% for 2 inches, and around 30% for the=20
Portland, OR metro area. The coastal ranges will likely receive=20
significant snowfall D2 reflected by a 50-70% chance for 4+ inches. Additionally, the continued moisture fetch onshore will bring=20
heavy snow again into the OR Cascades and northern CA ranges where=20
WPC probabilities for 6+ inches are at least 70%.

Then, during D3 /00Z Fri - 00Z Sat/ the closed low offshore WA/OR
opens, but remains amplified in response to a maxima and=20
accompanying shortwave trough rotating around it, through the base=20
of the trough, and onshore northern CA once again. This will be=20
accompanied by a renewed surge of deep layer ascent through=20
secondary jet intensification and downstream height=20
falls/divergence, to push another swath of heavy precipitation=20
onshore. Much of this will be in the vicinity of a surface low=20
which will develop just downstream of this vorticity lobe, and this
low is progged to move progressively northeast through the Great=20
Basin, reaching the Central Rockies by the end of the forecast=20
period. Snow levels will rise south and east of this low, but as it
tracks along a stationary front, there will likely be continued=20
low snow levels to the north, with an axis of frontogenesis and=20
accompanying enhanced ascent into a deepening DGZ driving a swath=20
of heavy snowfall across the area. A weaker AR will accompany this=20
low, reflected by GEFS and ECENS probabilities for 250 kg/m/s IVT=20
peaking around 70%, but this will still be sufficient to produce=20
heavy snow, especially in regions of upslope or the strongest fgen.
The global models still feature quite a bit of variability in=20
placement and timing for this second AR and low, so confidence in=20
is somewhat modest this far out. However, WPC probabilities are
already high (above 70%) for 12+ inches in the Sierra D3,
especially above 4000 ft. Heavy snow exceeding 6 inches is also
likely (>70%) for the ranges of NW WY.



...Upper Midwest/Great Lakes...=20
Day 2...

The lead shortwave ejecting downstream of the closed low west of
WA/OR will spin east out of Montana, reaching the Northern Plains
by Thursday morning and then racing east within pinched/progressive
flow to the Great Lakes Thursday night. This feature will help
spawn a weak wave of low pressure moving from the Northern Plains,
with accompanying downstream WAA and isentropic ascent resulting in
an expanding area of precipitation falling as snow on Thursday. The
overlap of synoptic lift with this isentropic ascent could result
in axis of heavy snow, especially along the international border
with Canada in MN and into WI and the U.P. of MI where the DGZ
depth is greatest as reflected by moderate probabilities (50-70%)
for at least 50mb of DGZ depth. The system is progressive which
will limit overall accumulations, but heavy rates of 1"/hr at times
will still produce heavy snow exceeding 4" as reflected by WPC
probabilities of 30-70% in the Arrowhead of MN, as well as the
Western U.P. of MI and Bayfield Peninsula of WI.


...Midwest to Northeast...
Days 2-3...

A fast moving upper-level disturbance over the Central Plains
Wednesday AM will be the primary feature in providing upper-level=20
ascent from the Midwest Wednesday evening to the Northeast on
Thursday. The progressive 500mb shortwave trough will be located
beneath the divergent left-exit quadrant of a roaring 150kt 250mb
jet streak located over the Rockies. At lower-levels, an 850mb
ridge over the subtropical Atlantic will work in tandem with
longwave 850mb troughing over the Northern Plains to create a 50kt
850mb jet over the Mississippi/Ohio River Valleys Wednesday night
that will act to deliver modest low-mid level moisture. NAEFS shows
IVT values by 06Z Thursday are topping 750 kg/m/s over the OH
Valley, which is above the 97.5 climatological percentile in the
CFSR climatology. In addition, 850-700mb WAA and 290K isentropic=20
glide amidst SWrly flow will lead to an gradual incline of the FGEN
axis over the OH Valley on east to the Mid- Atlantic Wednesday=20
evening. Last but not least in the overview of the key contributors
in this icy setup is the presence of a colder/dry air-mass that
will be anchored initially by a 1028+mb high that is above the 90th
percentile according to NAEFS. The high will be moving well
offshore by Thursday morning, but the linger cold-air damming
signature (CAD) will stick around for much of the event.

In these classic "overrunning a CAD wedge" setups, most guidance
tends to erode the <32F near-surface wet-bulb temperatures too
quick. Timing-wise, an icy wintry mix looks to get started in=20
northern IL around 00Z Thurs with some freezing drizzle, sleet, and
even light snow breaking out across the Ohio Valley and Mid-
Atlantic between 00-06Z Thurs. The heaviest FZRA occurs in the=20
Lower Great Lakes states between 03-09Z Thursday, then from the=20
central Appalachians to southeast PA and northern MD between=20
06-15Z. Sub- freezing surface temperatures will stick around=20
longest in the Laurel and Potomac Highlands, the Blue Ridge=20
Mountains, and into parts of the Shenandoah Valley where sub-=20
freezing air is harder to erode. By midday Thursday, a coastal low=20
begins to take shape off the Mid-Atlantic coast that would allow=20
for some Atlantic moisture to be advected into the Northeast=20
Thursday afternoon. The air-mass is more supportive of snow in=20
southern New England and as far north as the Adirondacks. While=20
most totals should generally be in the 2-4" range in these areas,=20
should the coastal low strengthen sooner, some mesoscale banding to
the north of the coastal low could occur over southern New=20
England.=20

Most guidance has come into better agreement on the timing
and amounts with a swath of >0.1" of ice accumulations from central
IL and across the Lower Great Lakes states to southeast PA. WPC
probabilities have focused on the Laurel and Potomac Highlands, as
well as parts of the Alleghenies and Blue Ridge as having the
better odds of seeing >0.25" ice accumulation. The Laurel Highland,
most notably, sport moderate chances (40-60%) for ice accumulations

0.25". Most ice accumulations that are observed will generally

fall below 0.25" but even amounts around 0.1" can result in
hazardous travel conditions. WPC probabilities show at least
moderate chance probabilities (>50%) for >0.1" of ice for northern
IN, northern OH, much of western PA (excluding areas south of
Pittsburgh), western VA, and along the Mason-Dixon line on east ot
I-83. There could be some portions of the western DC/Baltimore
suburbs that receive as much as 0.1" of ice as well for the
Thursday morning rush hour. The WSSI does depict Moderate Impact
potential (hazardous driving conditions and disruptions to daily
life such as closures/delays) in the DC/Baltimore metro areas,=20
particularly west of I-95 and north of I-66. Moderate Impacts are
also shown in the Laurel and Potomac Highlands, the Blue Ridge
Mountains, and the northern extent of the Shenandoah Valley. All
other areas previously mentioned from northern IL on east through
the Lower Great Lakes, central PA, and into New England are
forecast to see Minor Impacts from this event, highlighting the
potential for some slick roads and troublesome travel conditions.

Given the relatively large geographic coverage of at least 0.10"=20
ice potential and the increasing chances for over 0.25" of ice=20
accretion in parts of WV, MD, VA, and PA... Key Messages continue=20
for this event.

Weiss/Mullinax




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_gWTm10JCuUOHHJgr_CLDVIFJZ6S5pfdlnOoqN6hW_00q= Vq5hpB-ASusc25nG7Hn1QGVuPX4vPtu85GAtg2w1tYI1zo$=20

$$

=3D =3D =3D
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FOUS11 KWBC 050922
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
422 AM EST Wed Feb 5 2025

Valid 12Z Wed Feb 05 2025 - 12Z Sat Feb 08 2025

...Pacific Coast through the Northern Rockies and Northern Plains...
Days 1-3...

...Particularly active winter period across the west ends with a
potent low that tracks across California Thursday night, the
northern Rockies Friday, and the northern Plains Friday night...

Cold core low off the WA coast this morning shears into a
positively tilted trough through today from the zonal 150kt jet
streak to its south. Reinforcing shortwave energy takes the base=20
of the trough and pushes it through northern CA Thursday night as
another zonal jet streak intensifies sending the trough into the
northern Plains Friday night (before tracking through New England
Sunday).=20

Day 1: The low heights and SEly low level flow provide moderate=20
snow to the Cascades and PacNW Coastal Ranges through this=20
evening. Terrain enhancements allow 1"/hr rates there and snow
levels will be at or near sea level. Day 1 snow probs for >12" are
40-70% above about 2000ft in the OR Cascades and Klamath Mtns.=20
While Seattle and Portland have been generally spared impactful=20
snow through this cold phase so far, there are now 30-50% Day 1=20
snow probs for >2" in the Lowlands. Heavy snow continues this=20
morning over the Northern Rockies where probs for >8" additional=20
after 12Z are 40-70%, particularly in the Absarokas and Wind River.

Day 2: An atmospheric river with PW of 1" reaches the central CA=20
coast on Thursday south of the wave that consolidates and ejects=20
east. Another swath of heavy precipitation crosses CA with snow=20
levels over the Sierra Nevada rising to 6500ft by Thursday evening.
Day 2 snow probs for >18" are 50-80% for the Sierra Nevada and the Shasta/Siskiyou.

Another surface low track is then traceable through northern NV=20
early Friday which means more moderate to locally heavy snow for=20
interior southern Oregon and the Sawtooth/Salmon River and the
western WY ranges Thursday night through Friday where Day 2.5 snow
probs for >8" are 30-80%.

Day 3: The still positively-tilted trough shifts over the northern
High Plains Friday night with strong lee-side cyclogenesis tracking
over southern KS. Gulf moisture streams north up the Great Plains
ahead of this low and, combined with increasing upper divergence
including kissing jets over SD Friday evening, allows snow bands=20
to flourish over the Dakotas Friday night. Despite the progression
from the intensifying zonal jet to the south of trough, sufficient
cyclonic flow allows west-east bands to move with their=20
orientation and maximize snowfall over a somewhat narrow swath. The
GFS remains north of the Canadian with this axis depiction and the
EC is a bit more diffuse with the intensity. However, Day 3 probs=20
for 20-50% for >6" over northern SD are reasonable at this time.


...Upper Midwest/Great Lakes...=20
Days 1-2...

Lead shortwave downstream of the closed upper circulation off the=20
Pacific Northwest will eject downstream through the Northern Plains
later this afternoon with increased mid-level ascent focused=20
within the difluent axis ahead of the mean trough. A progressive=20
forward motion of the disturbance will limit the upper bounds of=20
the potential snowfall across the Upper Midwest into the Great=20
Lakes, however sufficient forcing and modest omega within a DGZ=20
depth of 50mb will generate snowfall rates capable of reaching=20
0.5-1"/hr during the height of the event. Snowfall will likely=20
break out after 18z with increased areal coverage as we move=20
through the evening today, ending the tail end of the D1 period.=20
Models have been insistent on the greatest potential over Northern=20
MN near the International border over into the Arrowhead, Bayfield=20
Peninsula of WI, and the U.P. of MI where synoptic snow persists=20
into Thursday morning. Latest WPC probabilities for >4" are running
between 40-70% with some small pockets of ~80% located over the MN
Arrowhead near the Canadian border and along the north shores of=20
Lake Superior. Lower probs exist for >6" of snowfall (10-40%)=20
within the same areas, but the progressive nature of the storm will
likely limit widespread heavier totals with more isolated pockets=20
of those higher totals in areas where banding persists the longest.
Very cold air with subterranean DGZ returns Thursday across Lake=20
Superior. LES continues into Friday for the U.P., but for now Day 2
snow probs for >4" are 30-60% for the Keweenaw Peninsula and the=20
eastern U.P.


...Midwest to Northeast including the Central Appalachians...
Days 1-2...

Progressive shortwave trough over southern CO early this morning=20
will rapidly advance eastward across the Great Plains today and
reach the Mid-Atlantic late tonight. Smaller shortwave=20
perturbations will also advect over the aforementioned regions with
lighter precip development over the Mid-Atlantic today ahead of=20
the main slug of moisture associated with the primary shortwave=20
trough. The separation of the deeper layer moisture can be inferred
from the higher IVT signatures advecting eastward into the Mid-=20
Atlantic, a solid +3 deviations according to the latest NAEFS=20
anomalies with values approaching 600-700 kg/ms on the 00z=20
GFS/ECMWF output. Moisture advection regime will be prominent=20
within the 925- 650mb layer as noted within relevant bufr soundings
within the zones of expected impact. A strengthening v-vector wind
component across the Southern Ohio Valley and points east into the
Central Mid- Atlantic indicate a prolific meridional response to=20
the amplifying 5H pattern as the trough approaches. 850mb LLJ being
forecast within the latest deterministic maintain posture of a=20
fairly robust 50-60kt jet core, a significant contributor to not=20
only the advection of moisture, but also of a prominent WAA regime=20
that will allow for a general mixed ptype pattern as we move=20
through the event this afternoon through Thursday.

Across the Ohio Valley and Mid-Atlantic, antecedent airmass under=20
the influence of a 1034mb surface high over Quebec will lead to=20
sufficient cooling within the lower confines of the boundary layer=20
with drier air focused within the 925-700mb layer, a setup that will=20
be come relevant with regards to anticipated wet bulb temperatures=20
as moisture from the west and southwest approaches. There is a=20
general consensus on the timing of the advancement of the precip=20
core for each region with the afternoon and early evening time frame=20
the initial stages for precip onset across the Midwest and Ohio=20
Valley as the main axis of difluence downstream of the approaching=20
mid-level shortwave provides focused ascent in-of the above areas.=20
Wintry precip is expected to breakout in the form of ZR over IL/IN=20
before shifting eastward into OH with an IP/ZR mix transitioning to=20
all ZR before precip field decays the very end of the D1 period.=20
Further east into the highlands of Western PA and WV, increasing=20
warm air advection pattern will transpire ahead of the trough with a=20
tongue of warmer air flooding a significant portion of the primary=20
thermal layers leading to primary ptype beginning as a liquid=20
hydrometeor. The issue becomes the cold air positioned within the=20
lowest confines of the PBL as the surface ridge to the north allows=20
for a filtering of a very shallow polar airmass across much of the=20 Mid-Atlantic and Northeast before shifting eastward as blocking=20
remains diffuse across the Northwest Atlantic. Anticipate=20
temperatures in the Laurel Highlands down through Western MD and the=20
High Country of WV to settle into the upper 20s prior to initial=20
precip with wet bulb temperatures within the range of 24-27F, a=20
textbook signature for prolonged ZR within the terrain leading to=20 significant ice accretion >0.25".=20

Across he central Mid-Atlantic east of the Blue Ridge,=20
temperatures will exhibit similar evolution with cold air filtering
east of the Appalachian front with a fresh cold/dry air injection=20
into the PBL leading to colder temperatures leading with widespread
upper 20s to low 30s readings likely as precip encroaches from the
west. Despite the high shifting off the coast, limited mixing=20
within the lower PBL will thwart a rapid warming of the primary=20
thermal layer located from the surface to 850mb, however the layers
above will be warm quickly with a sharp nose of WAA being progged=20
within the 850-650mb layer leading to a mixed ptype after perhaps a
very short window of light snow prior to the main moisture plume=20
reaching east of the mountains. IP/ZR combo will be present across=20
the Central Mid- Atlantic within the Piedmont with the majority of=20
precip shifting to all ZR prior to sunrise for all locations. The=20
question becomes the depth of the cold air and the process of cold=20
air damming within the confines of the northern Shenandoah to=20
places west of the Chesapeake over VA/MD/PA. The trends are for a=20
sharp delineation of prolonged freezing rain and rain along the=20
fall line northwest of I- 95 with greater potential for ice=20
accretion further northwest away from that marker. This will allow=20
for a sharp gradient in the ice accumulation forecast with <0.1"=20
likely east of the fall line, including the DC/Balt/Philadelphia=20
metros with >0.1" likely northwest with upwards of 0.2 plausible in
the topographically favored areas of the northern neck of VA, WV=20
Panhandle, Blue Ridge, Catoctins, and Parrs Ridge across NoVA up=20
through Central MD and far Southern PA.=20

Farther north and northeast across the Northern Mid-Atlantic,=20
initial burst of snow is anticipated before shifting to more IP and
ZR with IP being a more dominant ptype south of I-80 with snow=20
more common north and northeast of the interstate leading to WWD=20 probabilities for >4" to run between 40-60% for the higher=20
elevations of Upstate NY and Northern New England that include=20
areas like the Tug Hill, Adirondacks, Green and White Mountains of=20
VT/NH. Light ice accumulations are anticipated for a large area=20
encompassing much of the Northern Ohio Valley through the Mid-=20
Atlantic and Northeast. WPC probs for >0.1" of ice accretion is=20
between 40-70% across Northern Ohio Valley and the Piedmont east of
the Blue Ridge to the fall line northwest of I-95. Areas west of=20
the Blue Ridge to the Laurel Highlands of PA and Highlands of MD/WV
are upwards of 80-90% for similar totals with probs greater than=20
40% for >0.25" leading to Ice Storm Warning issuance this past=20
forecast cycle. Latest WSSI continues to predict a large area of at
least moderate impacts within those zones expecting greater than=20
0.2" of ice accretion due to impending disruptions in travel with=20
impacts that could include closures and delays that impact daily=20
life. Despite lighter accums further east into the Megalopolis,=20
light ice accumulations will still provide some hazardous travel=20
conditions for many during the Thursday AM commute. These impacts=20
will span through the Shenandoah Valley up through much of Central
and Eastern PA, highlighted by widespread Minor WSSI depictions=20
all across the affected areas.=20

Given the relatively large geographic coverage of at least 0.10" ice=20 potential and the increasing chances for over 0.25" of ice accretion=20
in parts of WV, MD, and PA, Key Messages continue for this event=20
which are linked below.


Jackson/Kleebauer



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages in the link below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8l1lpCDOEaPU5xsdUX7v8hnRE4k0S3pY5T3LNeH3W1qij= mZQC3DCZpJSPMK1DobMjIxw4FZBuuAlU8V3XGD0TnTX1BU$=20

$$

=3D =3D =3D
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FOUS11 KWBC 051954
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 PM EST Wed Feb 5 2025

Valid 12Z Wed Feb 05 2025 - 12Z Sat Feb 08 2025

...Pacific Coast through the Northern Rockies and Northern Plains...
Days 1-3...

...Active winter period across the west ends with a potent low=20
that tracks across California Thursday night, the northern Rockies=20
Friday, and the northern Plains Friday night...

The stormy pattern that has been ongoing across the West for
several days now will come to an end by this weekend. But until
then, periods of mountains and lowland snow will stick around the
Pacific Northwest this afternoon and evening thanks to an elongated
and positively tilted upper level trough over the northwest
Pacific. Farther south, a potent 500mb shortwave trough caught up
in the SWrly flow aloft will race towards California on Thursday.
NAEFS shows this system will have a healthy AR associated with it
and direct a >500 kg/m/s IVT (climatological percentiles topping
the 99th percentile) into the western U.S. Mandatory heights
associated with this trough are all below the 10th climatological
percentile as well, which should lead to a lowering of the snow
levels as it moves ashore on Friday. The heaviest snowfall in the
central and southern Sierra Nevada will generally reside above
6,000ft, while the northern Sierra Nevada and the
Shasta/Salmon/Siskiyou see heavy snowfall as low as 4,000ft in=20
some cases.=20

As the storm moves inland Friday morning, a cold Canadian air-mass
anchored by a 1030+mb high over the northern High Plains will be in
place, allowing for snow to the remain the primary precip type from
eastern Oregon and the Blue Mountains through the Sawtooth,
Bitterroots, Absaroka, Tetons, and Wind River Ranges. Snowfall=20
will be heavy in these ranges, including ranges farther south such=20
as the Bear River and Uinta ranges thanks to a highly anomalous IVT

300 kg/m/s (>99.5 climatological percentile at 18Z Fri) and these

ranges placement beneath the left-exit region of a 90kt 500mb jet=20
streak. Snow will push east through central and eastern Montana=20
Friday afternoon, then into the Dakotas by Friday night. Snowfall=20
rates will increase along the ND/SD border Friday night and into=20
Saturday morning as 850-700mb frontogenesis (FGEN) ensues and WAA=20
aloft supports heavy snow.

WPC probabilities through Saturday morning show high chance
probabilities (>70%) for snowfall totals >24" above 7,000ft in the
central and southern Sierra Nevada, and above 6,000ft in the
northern Sierra Nevada and Shasta ranges. Similar high chance
probabilities for >12" of snowfall are present in the Siskiyou and
Salmon mountains, as well as the Tetons, Bear River, and Wind=20
River Ranges. The Blue, Sawtooth, and Absaroka above 6,000ft are
also forecast to receive as much as a foot of snow, while the High
Plains of central and eastern Montana have moderate-to-high chances
(50-70%) for snowfall totals >4". The WSSI shows Major Impacts
(dangerous to impossible travel, widespread closures and
disruptions) along the spine of the Sierra Nevada, in the Siskiyou,
Salmon, Shasta, and southwest OR coastal ranges. There are
expansive areas of Moderate Impacts (hazardous driving conditions)
from the northern OR coastal ranges and along the OR Cascades on
east through most of the aforementioned Northern Rockies Ranges.
Minor Impacts are also being depicted at the moment in central and
eastern Montana for late Friday into Saturday.


...Northern Plains through the Great Lakes and Ohio Valley...=20
Days 1-3...

Potent shortwave trough (700mb heights falling below the 1st
percentile of the CFSR climatology according to NAEFS) will advect=20
across the Dakotas and into Minnesota Thursday and Thursday night=20
before racing east and out of the area by Friday morning. Rapid=20
height falls and impressive PVA downstream of a strung out lobe of=20
vorticity rounding the base of this trough will combine with the=20
LFQ of a modestly poleward arcing jet streak to produce large scale
ascent into the region. At the same time, moisture will increase=20
as modestly veered flow leads to robust moist isentropic ascent at=20
285-290K which will result in an expanding area of precipitation.=20
This precip will occur entirely as snow from ND through MI as the=20
column is quite cold, and the WAA accompanying this isentropic=20
ascent will help deepen the DGZ impressively (SREF probabilities=20
for 100mb of DGZ depth 30-70%, highest along the Canadian border).=20
This will result in high SLR snow accumulating rapidly as snowfall=20
rates may exceed 1"/hr at times (30-50% chance according to the=20
HREF). The system is progressive, limiting total accumulations, but
WPC probabilities indicate a 50-70% chance of at least 4 inches in
NE MN, including the Arrowhead, and into the western U.P. of MI.

Farther downstream and to the east, the accompanying WAA will
overrun a retreating high pressure to the east, leading to an axis
of moderate mixed precipitation from the Corn Belt into the Ohio
Valley. The WAA will lift rapidly northward, but will drive a brief
period of robust fgen, in the 925-700mb region, leading to a period
of moderate to heavy sleet/freezing rain before precipitation
changes over to rain. WPC probabilities D1 are as high as 50-70%
for 0.1" of ice, highest across north/central Ohio.

After a brief respite on D2, the progressive flow across much of
the CONUS will surge another winter storm system eastward into the
Northern Plains to begin D3. This system is progged to be much more
impressive as the potent driving trough ejects from the Pacific
Northwest and into the Northern Plains by Saturday morning. The
overall mid-level pattern across the Northern Plains is progged to
remain generally flat, but rapid height falls and a potent
subtropical jet streak reaching 150kts will help push IVT exceeding the
90th percentile from NAEFS into the region. At the same time,
strengthening WAA downstream of a low pressure moving across the
Central Plains will draw higher moisture northward, and the overlap
of this WAA with the diffluent portion of the upper jet streak will
produce a stripe of impressive 850-600mb fgen, efficiently lifting
ascent into a deepening DGZ (SREF probabilities for 100mb of depth
exceeding 30%). This will result in a swath of snow from the
Dakotas through Wisconsin, with an embedded band of heavier snow
likely. There is still quite a bit of longitudinal (timing) and
latitudinal (placement) uncertainty amongst the global members, but
ensembles suggest high confidence for this event and impactful snow
is likely across the Dakotas and into Minnesota/Wisconsin. WPC
probabilities have increased dramatically today, and now support a
high risk (>70%) for more than 6 inches D3 near Aberdeen, SD,
surrounded by a larger expanse of >50% from far western SD through
western WI.

Then farther to the southeast, the WAA will lift a warm nose more
robustly immediately downstream of the surface low into the Upper
Midwest and Ohio Valley. This will cause a stripe of mixed
precipitation to develop before the end of the period from Illinois
through eastern Ohio, and WPC probabilities increase once again,
now featuring a 30-50% chance for at least 0.01" from near
Davenport, IA through Cleveland, OH.


...Mid-Atlantic and Northeast...=20
Days 1-3...

Generally flat and fast flow within the mid-levels will dominate=20
the eastern half of the CONUS, keeping systems progressive into the
weekend. This will allow for a series of winter storms to impact
the region.

The first of these will develop tonight as a modest shortwave
trough ejects from the Central Plains and lifts E/NE across the
Ohio Valley, reaching New England Thursday evening. A weak jet
streak will accompany this feature as it moves east, producing some
subtly enhanced deep layer lift, but most of the ascent will be
driven instead by impressive 850mb warm advection, which will
intensify especially over New England Thursday afternoon. This WAA
overrunning a retreating high pressure will drive intensifying
isentropic ascent, especially within the 290-300K layer, and
moisture will be copious as reflected by mixing ratios exceeding
6g/kg. This will allow PWs surging northward from the Gulf of
Mexico to exceed the 90th, and in some places the 97th percentile
of the CFSR climatology according to NAEFS ensemble tables. At the
same time, a wave of low pressure will develop offshore and move up
the coast from NC to New England on Thursday, additional enhancing
ascent across the region.

As WAA/isentropic ascent increases, precipitation will overspread
the area from SW to NE, with a mixture of rain, snow, freezing
rain, and sleet expected. The p-type challenges are significant
with this event.=20

Across the Mid-Atlantic states, into Upstate NY, and as far north
as southern New England, precipitation will feature a mix of all
p-types, and sorting out the predominant is challenging. The column
initially starts cold enough that everywhere north of the Mason-
Dixon line could start as a burst of snow within the WAA, with
sleet the initial p-type farther south. What happens thereafter
makes the difference with respect to impacts. Although the high
retreats quickly, a wedge of high pressure will remain embedded
south into the Mid-Atlantic, and initially surface wet-bulb
temperatures are well below 0C due to large T-Td depressions. This
suggests that as precip begins, the wedge will be reinforced and
hold firmer than guidance indicates, despite the overwhelming=20
influence of the WAA. The high-res models have warmed a little bit=20
today compared to previous runs, but the initial cold depth is=20
still well above the 75th% percentile for freezing rain for parts=20
of VA/MD/PA, suggesting a long period of sleet before WAA wins out=20
turning precip over to ZR. Of course, farther north into PA and=20
Upstate NY may experience more IP than ZR, while the higher terrain
of WV/MD/PA (Appalachians, Alleghenies, and Laurel Highlands) have
the best chance for damaging freezing rain accretions due to being
above the cold layer. Overall, the system is progressive, but=20
significant QPF falling into the cold layer will produce=20
significant icing for the Mid-Atlantic with hazardous commutes=20
likely Thursday morning. WPC probabilities are moderate (30-50%)
for 0.25" in the central Appalachians, surrounded by a much larger
area of at least 50% for 0.01" or more across much of the Mid-
Atlantic and into southern New England. This event continues to be=20
the source of key messages linked below (Keymessage_1).

Farther north into Upstate NY and New England, much of the
precipitation is expected to fall as snow. The intensifying WAA=20
will result in a band of heavy snow as the resultant 850-700mb fgen
drives intense ascent into the DGZ just above. This will cause a
burst of snow lifting SW to NE Thursday, first in the Poconos, then
all points northeast, including New York City and Boston. Snowfall
rates within this burst could reach 1-2"/hr as reflected by the WPC
prototype snowband tool and HREF probabilities, but rapid=20
translation of this band northeast will somewhat limit total=20
accumulations. Still, substantial impacts are likely, and WPC
probabilities are high (>70%) for more than 4" of snow in the
higher terrain from the Adirondacks into the Greens and Whites,
with lesser accumulations likely in the lower elevations.

As this first low pulls away into Canada, a second wave of low
pressure moving across Ontario will drive a potent cold front
eastward from the Great Lakes and through New England Friday
morning/aftn. This cold front will have a two-pronged effect on
winter weather. First, the passage of the cold front may incite
some convective snow showers or snow squalls from Upstate NY
through Maine as low-level fgen and some modest 0-2km instability
combine in an area of elevated RH. This is reflected by the SnSq
parameter exceeding 1 Friday morning in this area. While
accumulations within any squalls will be limited, brief intense
snowfall rates could cause hazardous travel.=20

Then behind this front, increasing CAA on W/NW flow will cause
modest lake effect snow (LES), especially downstream of Lake
Ontario where water temps are still marginally warm (+5) while Lake
Erie is completely ice covered at this point. With 850mb temps
falling to as low as -15C, this will steepen lapse rates
sufficiently to produce heavy snow into the Tug Hill and western
Adirondacks, although total accumulations are expected to be
somewhat modest as reflected by WPC probabilities that are 50-70%
for 4 inches D1 and D2.

Finally, as the active pattern continues, another shortwave trough
will dig out of the Central Plains Saturday, reaching the eastern
Great Lakes/Ohio Valley by the end of the forecast period. In a
pattern similar to that on Thursday, an accompanying surface wave
will develop across the Ohio Valley and then track progressively
eastward. The downstream WAA will again be impressive, and surge
another round of mixed precipitation into the Mid-Atlantic states.
There is still quite a bit of uncertainty as to both timing and
placement of the heaviest snow and icing amounts Saturday, but
current WPC probabilities indicate a moderate risk (30-50%) for at
least 0.01 inches from central VA through southern PA.


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5gCMie6L0ODqw7xDgP4Z53w5livP4KYNj0fZqouup9Z0v= A5pkdxiTtbZyxnREAlqbJha6dVppLuP8-lATjM2lD-QkSo$=20

$$

=3D =3D =3D
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FOUS11 KWBC 052136
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 PM EST Wed Feb 5 2025

Valid 00Z Thu Feb 06 2025 - 00Z Sun Feb 09 2025

...Pacific Coast through the Northern Rockies and Northern Plains...
Days 1-3...

...Active winter period across the west ends with a potent low=20
that tracks across California Thursday night, the northern Rockies=20
Friday, and the northern Plains Friday night...

The stormy pattern that has been ongoing across the West for
several days now will come to an end by this weekend. But until
then, periods of mountains and lowland snow will stick around the
Pacific Northwest this afternoon and evening thanks to an elongated
and positively tilted upper level trough over the northwest
Pacific. Farther south, a potent 500mb shortwave trough caught up
in the SWrly flow aloft will race towards California on Thursday.
NAEFS shows this system will have a healthy AR associated with it
and direct a >500 kg/m/s IVT (climatological percentiles topping
the 99th percentile) into the western U.S. Mandatory heights
associated with this trough are all below the 10th climatological
percentile as well, which should lead to a lowering of the snow
levels as it moves ashore on Friday. The heaviest snowfall in the
central and southern Sierra Nevada will generally reside above
6,000ft, while the northern Sierra Nevada and the
Shasta/Salmon/Siskiyou see heavy snowfall as low as 4,000ft in=20
some cases.=20

As the storm moves inland Friday morning, a cold Canadian air-mass
anchored by a 1030+mb high over the northern High Plains will be in
place, allowing for snow to the remain the primary precip type from
eastern Oregon and the Blue Mountains through the Sawtooth,
Bitterroots, Absaroka, Tetons, and Wind River Ranges. Snowfall=20
will be heavy in these ranges, including ranges farther south such=20
as the Bear River and Uinta ranges thanks to a highly anomalous IVT

300 kg/m/s (>99.5 climatological percentile at 18Z Fri) and these

ranges placement beneath the left-exit region of a 90kt 500mb jet=20
streak. Snow will push east through central and eastern Montana=20
Friday afternoon, then into the Dakotas by Friday night. Snowfall=20
rates will increase along the ND/SD border Friday night and into=20
Saturday morning as 850-700mb frontogenesis (FGEN) ensues and WAA=20
aloft supports heavy snow.

WPC probabilities through Saturday morning show high chance
probabilities (>70%) for snowfall totals >24" above 7,000ft in the
central and southern Sierra Nevada, and above 6,000ft in the
northern Sierra Nevada and Shasta ranges. Similar high chance
probabilities for >12" of snowfall are present in the Siskiyou and
Salmon mountains, as well as the Tetons, Bear River, and Wind=20
River Ranges. The Blue, Sawtooth, and Absaroka above 6,000ft are
also forecast to receive as much as a foot of snow, while the High
Plains of central and eastern Montana have moderate-to-high chances
(50-70%) for snowfall totals >4". The WSSI shows Major Impacts
(dangerous to impossible travel, widespread closures and
disruptions) along the spine of the Sierra Nevada, in the Siskiyou,
Salmon, Shasta, and southwest OR coastal ranges. There are
expansive areas of Moderate Impacts (hazardous driving conditions)
from the northern OR coastal ranges and along the OR Cascades on
east through most of the aforementioned Northern Rockies Ranges.
Minor Impacts are also being depicted at the moment in central and
eastern Montana for late Friday into Saturday.


...Northern Plains through the Great Lakes and Ohio Valley...=20
Days 1-3...

Potent shortwave trough (700mb heights falling below the 1st
percentile of the CFSR climatology according to NAEFS) will advect=20
across the Dakotas and into Minnesota Thursday and Thursday night=20
before racing east and out of the area by Friday morning. Rapid=20
height falls and impressive PVA downstream of a strung out lobe of=20
vorticity rounding the base of this trough will combine with the=20
LFQ of a modestly poleward arcing jet streak to produce large scale
ascent into the region. At the same time, moisture will increase=20
as modestly veered flow leads to robust moist isentropic ascent at=20
285-290K which will result in an expanding area of precipitation.=20
This precip will occur entirely as snow from ND through MI as the=20
column is quite cold, and the WAA accompanying this isentropic=20
ascent will help deepen the DGZ impressively (SREF probabilities=20
for 100mb of DGZ depth 30-70%, highest along the Canadian border).=20
This will result in high SLR snow accumulating rapidly as snowfall=20
rates may exceed 1"/hr at times (30-50% chance according to the=20
HREF). The system is progressive, limiting total accumulations, but
WPC probabilities indicate a 50-70% chance of at least 4 inches in
NE MN, including the Arrowhead, and into the western U.P. of MI.

Farther downstream and to the east, the accompanying WAA will
overrun a retreating high pressure to the east, leading to an axis
of moderate mixed precipitation from the Corn Belt into the Ohio
Valley. The WAA will lift rapidly northward, but will drive a brief
period of robust fgen, in the 925-700mb region, leading to a period
of moderate to heavy sleet/freezing rain before precipitation
changes over to rain. WPC probabilities D1 are as high as 50-70%
for 0.1" of ice, highest across north/central Ohio.

After a brief respite on D2, the progressive flow across much of
the CONUS will surge another winter storm system eastward into the
Northern Plains to begin D3. This system is progged to be much more
impressive as the potent driving trough ejects from the Pacific
Northwest and into the Northern Plains by Saturday morning. The
overall mid-level pattern across the Northern Plains is progged to
remain generally flat, but rapid height falls and a potent
subtropical jet streak reaching 150kts will help push IVT exceeding the
90th percentile from NAEFS into the region. At the same time,
strengthening WAA downstream of a low pressure moving across the
Central Plains will draw higher moisture northward, and the overlap
of this WAA with the diffluent portion of the upper jet streak will
produce a stripe of impressive 850-600mb fgen, efficiently lifting
ascent into a deepening DGZ (SREF probabilities for 100mb of depth
exceeding 30%). This will result in a swath of snow from the
Dakotas through Wisconsin, with an embedded band of heavier snow
likely. There is still quite a bit of longitudinal (timing) and
latitudinal (placement) uncertainty amongst the global members, but
ensembles suggest high confidence for this event and impactful snow
is likely across the Dakotas and into Minnesota/Wisconsin. WPC
probabilities have increased dramatically today, and now support a
high risk (>70%) for more than 6 inches D3 near Aberdeen, SD,
surrounded by a larger expanse of >50% from far western SD through
western WI.

Then farther to the southeast, the WAA will lift a warm nose more
robustly immediately downstream of the surface low into the Upper
Midwest and Ohio Valley. This will cause a stripe of mixed
precipitation to develop before the end of the period from Illinois
through eastern Ohio, and WPC probabilities increase once again,
now featuring a 30-50% chance for at least 0.01" from near
Davenport, IA through Cleveland, OH.


...Mid-Atlantic and Northeast...=20
Days 1-3...

Generally flat and fast flow within the mid-levels will dominate=20
the eastern half of the CONUS, keeping systems progressive into the
weekend. This will allow for a series of winter storms to impact
the region.

The first of these will develop tonight as a modest shortwave
trough ejects from the Central Plains and lifts E/NE across the
Ohio Valley, reaching New England Thursday evening. A weak jet
streak will accompany this feature as it moves east, producing some
subtly enhanced deep layer lift, but most of the ascent will be
driven instead by impressive 850mb warm advection, which will
intensify especially over New England Thursday afternoon. This WAA
overrunning a retreating high pressure will drive intensifying
isentropic ascent, especially within the 290-300K layer, and
moisture will be copious as reflected by mixing ratios exceeding
6g/kg. This will allow PWs surging northward from the Gulf of
Mexico to exceed the 90th, and in some places the 97th percentile
of the CFSR climatology according to NAEFS ensemble tables. At the
same time, a wave of low pressure will develop offshore and move up
the coast from NC to New England on Thursday, additional enhancing
ascent across the region.

As WAA/isentropic ascent increases, precipitation will overspread
the area from SW to NE, with a mixture of rain, snow, freezing
rain, and sleet expected. The p-type challenges are significant
with this event.=20

Across the Mid-Atlantic states, into Upstate NY, and as far north
as southern New England, precipitation will feature a mix of all
p-types, and sorting out the predominant is challenging. The column
initially starts cold enough that everywhere north of the Mason-
Dixon line could start as a burst of snow within the WAA, with
sleet the initial p-type farther south. What happens thereafter
makes the difference with respect to impacts. Although the high
retreats quickly, a wedge of high pressure will remain embedded
south into the Mid-Atlantic, and initially surface wet-bulb
temperatures are well below 0C due to large T-Td depressions. This
suggests that as precip begins, the wedge will be reinforced and
hold firmer than guidance indicates, despite the overwhelming=20
influence of the WAA. The high-res models have warmed a little bit=20
today compared to previous runs, but the initial cold depth is=20
still well above the 75th% percentile for freezing rain for parts=20
of VA/MD/PA, suggesting a long period of sleet before WAA wins out=20
turning precip over to ZR. Of course, farther north into PA and=20
Upstate NY may experience more IP than ZR, while the higher terrain
of WV/MD/PA (Appalachians, Alleghenies, and Laurel Highlands) have
the best chance for damaging freezing rain accretions due to being
above the cold layer. Overall, the system is progressive, but=20
significant QPF falling into the cold layer will produce=20
significant icing for the Mid-Atlantic with hazardous commutes=20
likely Thursday morning. WPC probabilities are moderate (30-50%)
for 0.25" in the central Appalachians, surrounded by a much larger
area of at least 50% for 0.01" or more across much of the Mid-
Atlantic and into southern New England. This event continues to be=20
the source of key messages linked below (Keymessage_1).

Farther north into Upstate NY and New England, much of the
precipitation is expected to fall as snow. The intensifying WAA=20
will result in a band of heavy snow as the resultant 850-700mb fgen
drives intense ascent into the DGZ just above. This will cause a
burst of snow lifting SW to NE Thursday, first in the Poconos, then
all points northeast, including New York City and Boston. Snowfall
rates within this burst could reach 1-2"/hr as reflected by the WPC
prototype snowband tool and HREF probabilities, but rapid=20
translation of this band northeast will somewhat limit total=20
accumulations. Still, substantial impacts are likely, and WPC
probabilities are high (>70%) for more than 4" of snow in the
higher terrain from the Adirondacks into the Greens and Whites,
with lesser accumulations likely in the lower elevations.

As this first low pulls away into Canada, a second wave of low
pressure moving across Ontario will drive a potent cold front
eastward from the Great Lakes and through New England Friday
morning/aftn. This cold front will have a two-pronged effect on
winter weather. First, the passage of the cold front may incite
some convective snow showers or snow squalls from Upstate NY
through Maine as low-level fgen and some modest 0-2km instability
combine in an area of elevated RH. This is reflected by the SnSq
parameter exceeding 1 Friday morning in this area. While
accumulations within any squalls will be limited, brief intense
snowfall rates could cause hazardous travel.=20

Then behind this front, increasing CAA on W/NW flow will cause
modest lake effect snow (LES), especially downstream of Lake
Ontario where water temps are still marginally warm (+5) while Lake
Erie is completely ice covered at this point. With 850mb temps
falling to as low as -15C, this will steepen lapse rates
sufficiently to produce heavy snow into the Tug Hill and western
Adirondacks, although total accumulations are expected to be
somewhat modest as reflected by WPC probabilities that are 50-70%
for 4 inches D1 and D2.

Finally, as the active pattern continues, another shortwave trough
will dig out of the Central Plains Saturday, reaching the eastern
Great Lakes/Ohio Valley by the end of the forecast period. In a
pattern similar to that on Thursday, an accompanying surface wave
will develop across the Ohio Valley and then track progressively
eastward. The downstream WAA will again be impressive, and surge
another round of mixed precipitation into the Mid-Atlantic states.
There is still quite a bit of uncertainty as to both timing and
placement of the heaviest snow and icing amounts Saturday, but
current WPC probabilities indicate a moderate risk (30-50%) for at
least 0.01 inches from central VA through southern PA.


Weiss/Mullinax


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5tPhRn2Zs7FAIu5VEjJyezLhh0L0FF0Y7B7p7Cjz_8zGx= rF-KHEmuJ7rmyzHAssvmGm33xyd99gfS9LjWbDw3jIVJcY$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!5tPhRn2Zs7FAIu5VEjJyezLhh0L0FF0Y7B7p7Cjz_8zGx= rF-KHEmuJ7rmyzHAssvmGm33xyd99gfS9LjWbDw9DeXYzM$=20

$$

=3D =3D =3D
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FOUS11 KWBC 090835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EST Sun Feb 9 2025

Valid 12Z Sun Feb 09 2025 - 12Z Wed Feb 12 2025

...Great Lakes and Northeast...
Days 1-2...

A significant winter storm will wind down this morning across New
England as an area of low pressure pulls away from southern New
England leading to rapid drying and renewed CAA. Light snow should
finally come to an end along coastal regions by about 16z or so.
However, the CAA behind the accompanying cold front will setup an
environment favorable for LES E/SE of Lake Ontario and SE Lake
Superior. Shifting winds (more N/NW early, becoming more W D2 and
weakening by D3) will result in a shifting band of LES. Latest
Great Lakes ice analysis shows Lake Ontario remaining mostly ice
free with surface water temperatures around 3 to 4 degrees C. For
D1, the most significant accumulations are likely in the northern
Finger Lakes region, where they have a 70-90% chance of exceeding
4" near the lake shore, with D3 probabilities for 4+ inches
reaching 50-70% focused in the Tug Hill Plateau. Additionally,
probabilities for 4+ inches are 30-50% D1-2 across the Keweenaw
Peninsula and near Whitefish Point in the U.P. of MI.


...Central Plains through the Mid-Atlantic...
Days 2-3...

The next in this parade of systems across the CONUS begins to
develop D2/Monday as a shortwave trough ejects from near Baja and
then moves east into the Southern Plains by Tuesday evening. This
shortwave will remain embedded within a longwave trough axis as it
moves east through its evolution, but 00z guidance has trended
slightly more amplified with the longwave pattern. This subtle change
can be traced to a more consolidated western trough and faster Pac
NW shortwave that pumps up the eastern U.S. ridge ever so slightly
in order to prompt more southwesterly upper flow as opposed to
straight zonal winds. This trend, should it persist, would give the
impressive IVT (up to the 97.5th climatological percentile per the
12z NAEFS) the ability to bring the precipitation shield a bit
farther north across the Ohio Valley and Mid-Atlantic, where snow
is the dominant ptype. Additionally, upper diffluence will likely
increase with time as a downstream jet streak intensifies towards
150kts and arcs sufficiently poleward while leaving its tail across
the Central Plains and into the Lower MS VLY by Tuesday evening.
This will provide additional deep layer ascent as the system
organizes over the Mid-Atlantic through D3 and promoting a longer
duration moderate to heavy snowfall. Snow ratios for a majority of
the event are expected to remain around climo or slightly below
(8-11:1) due to an elevated DGZ and strong winds through it. So,
the main question remains how far north and how heavy QPF is should
the more amplified trend continue.

Light snow is expected to develop first across the central Plains
and Mid-Mississippi Valley on D2 as the upper jet begins to
intensify over the central U.S., which then begins to quickly
expand eastward into the Mid-Atlantic and central Appalachians on
D3.

WPC probabilities at this time for snowfall are highest for 4+
inches in the higher elevations of WV/VA where they peak above 70%,
and locally 6+ inches of snow is possible. Elsewhere, WPC
probabilities for 4" have increased and reach 40-60% across
central/northern VA, MD, and DE. Probabilities for at least 2" are
low 10-20% across the central Plains and Mid-Mississippi Valley,
but increase to above 70% across eastern KY and western WV.

There also exists the potential for an area of mixed ptype
associated with this system, one over the Ozarks of AR and a more
impressive area extending from western NC to southwest VA. The set
up supports a potentially significant ice storm in the Piedmont
and Foot Hills of the central/southern Appalachians where a
classic CAD setup and overrunning precip combine to create an
environment ripe for freezing rain. Large high pressure spanning
across the northern and eastern U.S. through Tuesday will
consolidate and reposition over southern Quebec by early Wednesday.
As a constant flow of precipitation remains aimed at the southern
Appalachians, cold northerly flow at the surface also continues
along and just east of the Blue Ridge Mts. while modest mid-level south-southwesterly flow brings the warm nose into central VA. As
a result, WPC probabilities for at least 0.25" of ice have
increased to around 20-40% from northwest NC to much of southwest
VA east of the continental divide. Additional freezing rain is also
likely during the period following D3, with moderate- level WSSI-P
values up to 40-60%. Lower probabilities of 10-30% for at least
0.1" of ice exist across the AR Ozarks.


...Central Rockies and Central Plains...
Day 3...

Another winter storm will quickly develop by the end of D3 (Tuesday
night) across the central Rockies/Plains as the aforementioned long
wave trough over the West begins to lift northeastward due to
interacting shortwaves initially over the Northeast and near
northern Baja California. This interaction reinvigorates the
extended and strong jet streak arching from the Mid-Mississippi
Valley to New England, prompting optimal upper diffluence in the
central Plains. At the surface, large high pressure up to the 99th climatological percentile per the 12z NAEFS will supply cold air
throughout much of the Plains and a cold front well south to the
Southern Plains. Thus, forcing will be mostly elevated and for the
northern parts of the precipitation shield a very deep DGZ (over
300 mb for parts of KS, NE, and IA Monday morning per the 00z GFS)
and very light winds could support snow ratios well above climo.
WPC probabilities through the end of the forecast period (12z
Wednesday) reach above 70% in the highest terrain of the CO Rockies
and are 40-70% for much of western and central KS, with the
majority of snowfall expected from this event after 12z Wednesday.


Snell



$$

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FOUS11 KWBC 092022
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 PM EST Sun Feb 9 2025

Valid 12Z Sun Feb 09 2025 - 12Z Wed Feb 12 2025

...Great Lakes...
Days 1-2...

Low pressure exiting New England this afternoon will be followed
almost immediately by a secondary shortwave racing across the Great
Lakes and across New England on Monday morning, with a third
impulse racing across the region Tuesday morning as
flat/progressive flow persists across the CONUS. Each of these
subsequent shortwaves will be accompanied by a weak cold front,
driving enhanced CAA across the Great Lakes to support periods of
lake effect snow (LES). On D1, 850mb temps fall to -15C or more,
steepening low-level lapse rates sufficiently to lift inversion
levels to nearly 10,000 ft, which with ascent maximizing into the
lowering DGZ will cause bands of heavy snow with rates of 1"/hr or
more across the U.P. of MI, as well as SE of Lake Ontario and into
the northern Finger Lakes region. WPC probabilities D1 are high

70%) for 6+ inches along the SE lake shore of Ontario, as well as

across the Keweenaw Peninsula of the U.P. of MI.

During D2, the next impulses pushes across the Northern Great
Lakes and into Ontario, Canada, driving a stronger cold front
across the Great Lakes. 850mb temperatures behind this front drop
even more significantly, to as low as -25C over Lake Superior and
-15 to -20C farther east. Despite lake surface temperatures that
are continuing to cool, this will again support renewed LES, and
WPC probabilities are again high (>70%) for 6 inches, but focused a
bit farther north into the Tug Hill Plateau.


...Mid-Mississippi Valley to the Mid-Atlantic...
Days 2-3...

Confluent mid-level pattern will maintain progressive flow across
the CONUS as the next in this parade of storms develops over the
Central Plains Monday evening. This system will strengthen in
response to vorticity energy shedding from the base of a longwave
trough initially over Baja, combining with the RRQ of a southern
stream jet streak which begins to amplify and arc meridionally,
leaving favorable diffluence atop the mid-level PVA/divergence. The
downstream confluence of the northern and southern streams should
result in suppression of this wave, keeping it fast and generally
flat from west to east, but will also result in significant ascent
and a prolonged period of precipitation as isentropic ascent from
the Gulf surges northward and spokes of vorticity continue to lag
back to the SW leaving a long duration of ascent.

The trends for this system had been steadily southward, but
overnight and early runs today have started to trend a bit farther
north, especially into the Mid-Atlantic. This appears to be in
response, as noted by the previous shift, a deeper/faster Pacific
NW shortwave interacting with the Baja trough more significantly.
This has led to stronger height falls over the Intermountain West
by Tuesday aftn, with downstream ridging pulsing more strongly
northward into the Ohio Valley/Mid-Atlantic. At this time, the
surface features appear modest Tue/Wed, so expect there is some
maximum latitudinal push of this precipitation, but will need to
continue to monitor trends to determine where the heaviest
precipitation will occur, as well as how far north the accompanying
WAA will push.

Based on current guidance, this is beginning to look like a
significant winter event containing snow and sleet and freezing
rain, generally from the Ozarks almost due east into the Central
Appalachians and the I-95 corridor from Richmond, VA to Baltimore,
MD. The downstream confluence of the mid-level pattern will force
this generally west-to-east axis of heavy precipitation, with
290-295K isentropic ascent and accompanying WAA fueling the
elevated PWs progged by NAEFS to exceed the 90th climatological
percentile as far north as the TN VLY and southern Mid-Atlantic
(NC/VA border). This will supply plentiful moisture for heavy
precipitation, and the sharpening baroclinicity on the WAA leading
to impressive 850-700mb fgen will help to concurrently enhance
ascent. This suggests that precipitation rates will be heavy at
times, although in areas with snow the DGZ appears elevated and the
best fgen is well below that, which when combined with modestly
"warm" temperatures should keep SLRs low and this could be a heavy
and wet snow for most of the area. Although guidance has struggled
with any consistency so far, and further updates are likely,
current WPC probabilities are high (>70%) in the Central
Appalachians D2, and remain high while extending into the Mid-
Atlantic D3 for 4+ inches. This includes the area between Richmond
and Philadelphia.

Farther to the south, there is likely to be a transition zone from
rain to snow which will include axes of moderate to heavy freezing
rain, especially in the higher elevations around the Ozarks, as
well as across portions of the Central Appalachians from eastern KY
through SW VA. There remains a lot of uncertainty as to the
amounts of icing, especially noting that rates could be heavy at
times which don't efficiently accrete, and with the general
synoptic uncertainty continuing, but there is high confidence

70%) for warning-level icing (above 0.25") of ice in SW VA, with

locally as much as 0.5" of damaging ice possible.

As vorticity lobes continue to shed eastward from the Baja trough,
and as the developing full latitude trough (merging northern and
southern streams over the Intermountain West) lags the first
impulse, a second system with additional precipitation will
approach this same area from the SW late D3 /Wednesday aftn./ This
will again produce an axis of all p-types from the Ozarks eastward
to the Mid-Atlantic, and its possible in some areas there will not
even be much of a break before this second impulse. The Wednesday
system developing in the Central Plains will likely be more intense
with respect to the surface feature, so more warm air should flood
northward downstream, but the evolution of this second wave will
be somewhat dependent on the track of the first event. At this
time, WPC probabilities for 0.1" of freezing rain D3 generally just
feature patch 10-30% from the Ozarks into northern KY.


...Central Rockies/Plains/Mid-MS Valley...
Days 2-3...

As the longwave trough over the West passes the Rockies Tuesday
into Wednesday, precipitation will expand across the central
Plains. Snow over the Rockies will accumulate several inches
Tuesday afternoon and overnight through early Wednesday over the
Medicine Bow mountains with at least 6 inches above 10,000ft likely
(probs >50%). Positive tilt and broad SW flow will favor a
progressive system D3, but the potential exists for moderate to
heavy snow across much of Kansas Tuesday night into Wednesday.
Upper jet will extend from TX northeastward to the Midwest with
speed divergence over the Plains helping to promote ascent into a
moistening column on WAA from the south in the lower levels. A
large high pressure to the north will supply NE winds to the region
but the gradient is not expected to be strong enough to produce
much blowing snow. By early Wednesday, snow could fall heavy at
times over central KS as favorable FGEN aligns with sufficient lift
into a potentially very deep DGZ and/or isothermal layer, but
these smaller scale features are hard to pinpoint this far out. In
addition, SLRs may be close to 20:1 or higher in these favorable
areas but otherwise waver around 15:1 given the colder air mass.
Northern edge of the precipitation shield has more uncertainty at
this point but a blend of the latest guidance offered a reasonable
starting point, with tapering amounts of snow into Nebraska. WPC
probabilities of at least 4 inches of snow are >50% over nearly all
of KS and focused along I-70 right into the Kansas City, MO area
as well (continuing into D4). Within this same region, lower
probabilities (10-50%) of at least 8 inches of snow are present.
Snowfall will expand rather quickly to the northeast toward the
Chicago metro by Wednesday afternoon/evening where WPC
probabilities

Southern side of the precipitation shield over OK and into the
Ozarks will likely be more marginal, and a mix or sleet and
freezing rain is likely due to the overrunning of the cold surface
with warmer air aloft. There, WPC probabilities of at least 0.10"
icing are low (10-30%).


...Pacific Coast...
Day 3...

Although still far out in time with limited confidence, it appears
the West will begin to become more active again mid-to-late week
as moisture begins to stream onshore from the Pacific. During D3,
there is considerable spread as to where the best moisture plume
will go as it gets restricted to the SW on the periphery of a large
trough over the CONUS and beneath a short-wavelength ridge over
the Pacific Northwest. At the same time, a deepening trough over
the Pacific will begin to track eastward, leading to a push of
moisture a bit farther NW and into southern/central CA. This could
result in some light to moderate snow reaching the Sierra before
00Z Thursday, but unquestionably more active weather with much
heavier snow will develop beyond this current forecast period. At
this time, WPC probabilities are moderate (30-50%) for 6+ inches in
the Sierra, generally above what could be very low snow levels of
2000-2500 ft.



Weiss/Fracasso



$$

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FOUS11 KWBC 092321
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
621 PM EST Sun Feb 9 2025

Valid 00Z Mon Feb 10 2025 - 00Z Thu Feb 13 2025

...Great Lakes...
Days 1-2...

Low pressure exiting New England this afternoon will be followed=20
almost immediately by a secondary shortwave racing across the Great
Lakes and across New England on Monday morning, with a third=20
impulse racing across the region Tuesday morning as=20
flat/progressive flow persists across the CONUS. Each of these=20
subsequent shortwaves will be accompanied by a weak cold front,=20
driving enhanced CAA across the Great Lakes to support periods of=20
lake effect snow (LES). On D1, 850mb temps fall to -15C or more,=20
steepening low-level lapse rates sufficiently to lift inversion=20
levels to nearly 10,000 ft, which with ascent maximizing into the=20
lowering DGZ will cause bands of heavy snow with rates of 1"/hr or=20
more across the U.P. of MI, as well as SE of Lake Ontario and into=20
the northern Finger Lakes region. WPC probabilities D1 are high=20

70%) for 6+ inches along the SE lake shore of Ontario, as well as

across the Keweenaw Peninsula of the U.P. of MI.

During D2, the next impulses pushes across the Northern Great=20
Lakes and into Ontario, Canada, driving a stronger cold front=20
across the Great Lakes. 850mb temperatures behind this front drop=20
even more significantly, to as low as -25C over Lake Superior and=20
-15 to -20C farther east. Despite lake surface temperatures that=20
are continuing to cool, this will again support renewed LES, and=20
WPC probabilities are again high (>70%) for 6 inches, but focused a
bit farther north into the Tug Hill Plateau.


...Mid-Mississippi Valley to the Mid-Atlantic...=20
Days 2-3...

Confluent mid-level pattern will maintain progressive flow across=20
the CONUS as the next in this parade of storms develops over the=20
Central Plains Monday evening. This system will strengthen in=20
response to vorticity energy shedding from the base of a longwave=20
trough initially over Baja, combining with the RRQ of a southern=20
stream jet streak which begins to amplify and arc meridionally,=20
leaving favorable diffluence atop the mid-level PVA/divergence. The
downstream confluence of the northern and southern streams should=20
result in suppression of this wave, keeping it fast and generally=20
flat from west to east, but will also result in significant ascent=20
and a prolonged period of precipitation as isentropic ascent from=20
the Gulf surges northward and spokes of vorticity continue to lag=20
back to the SW leaving a long duration of ascent.

The trends for this system had been steadily southward, but=20
overnight and early runs today have started to trend a bit farther=20
north, especially into the Mid-Atlantic. This appears to be in=20
response, as noted by the previous shift, a deeper/faster Pacific=20
NW shortwave interacting with the Baja trough more significantly.=20
This has led to stronger height falls over the Intermountain West=20
by Tuesday aftn, with downstream ridging pulsing more strongly=20
northward into the Ohio Valley/Mid-Atlantic. At this time, the=20
surface features appear modest Tue/Wed, so expect there is some=20
maximum latitudinal push of this precipitation, but will need to=20
continue to monitor trends to determine where the heaviest=20
precipitation will occur, as well as how far north the accompanying
WAA will push.

Based on current guidance, this is beginning to look like a=20
significant winter event containing snow and sleet and freezing=20
rain, generally from the Ozarks almost due east into the Central=20 Appalachians and the I-95 corridor from Richmond, VA to Baltimore,=20
MD. The downstream confluence of the mid-level pattern will force=20
this generally west-to-east axis of heavy precipitation, with=20
290-295K isentropic ascent and accompanying WAA fueling the=20
elevated PWs progged by NAEFS to exceed the 90th climatological=20
percentile as far north as the TN VLY and southern Mid-Atlantic=20
(NC/VA border). This will supply plentiful moisture for heavy=20
precipitation, and the sharpening baroclinicity on the WAA leading=20
to impressive 850-700mb fgen will help to concurrently enhance=20
ascent. This suggests that precipitation rates will be heavy at=20
times, although in areas with snow the DGZ appears elevated and the
best fgen is well below that, which when combined with modestly=20
"warm" temperatures should keep SLRs low and this could be a heavy=20
and wet snow for most of the area. Although guidance has struggled=20
with any consistency so far, and further updates are likely,=20
current WPC probabilities are high (>70%) in the Central=20
Appalachians D2, and remain high while extending into the Mid-=20
Atlantic D3 for 4+ inches. This includes the area between Richmond=20
and Philadelphia.=20

Farther to the south, there is likely to be a transition zone from
rain to snow which will include axes of moderate to heavy freezing
rain, especially in the higher elevations around the Ozarks, as=20
well as across portions of the Central Appalachians from eastern KY
through SW VA. There remains a lot of uncertainty as to the=20
amounts of icing, especially noting that rates could be heavy at=20
times which don't efficiently accrete, and with the general=20
synoptic uncertainty continuing, but there is high confidence=20

70%) for warning-level icing (above 0.25") of ice in SW VA, with=20

locally as much as 0.5" of damaging ice possible.

As vorticity lobes continue to shed eastward from the Baja trough,
and as the developing full latitude trough (merging northern and=20
southern streams over the Intermountain West) lags the first=20
impulse, a second system with additional precipitation will=20
approach this same area from the SW late D3 /Wednesday aftn./ This=20
will again produce an axis of all p-types from the Ozarks eastward=20
to the Mid-Atlantic, and its possible in some areas there will not=20
even be much of a break before this second impulse. The Wednesday=20
system developing in the Central Plains will likely be more intense
with respect to the surface feature, so more warm air should flood
northward downstream, but the evolution of this second wave will=20
be somewhat dependent on the track of the first event. At this=20
time, WPC probabilities for 0.1" of freezing rain D3 generally just
feature patch 10-30% from the Ozarks into northern KY.


...Central Rockies/Plains/Mid-MS Valley...=20
Days 2-3...

As the longwave trough over the West passes the Rockies Tuesday=20
into Wednesday, precipitation will expand across the central=20
Plains. Snow over the Rockies will accumulate several inches=20
Tuesday afternoon and overnight through early Wednesday over the=20
Medicine Bow mountains with at least 6 inches above 10,000ft likely
(probs >50%). Positive tilt and broad SW flow will favor a=20
progressive system D3, but the potential exists for moderate to=20
heavy snow across much of Kansas Tuesday night into Wednesday.=20
Upper jet will extend from TX northeastward to the Midwest with=20
speed divergence over the Plains helping to promote ascent into a=20
moistening column on WAA from the south in the lower levels. A=20
large high pressure to the north will supply NE winds to the region
but the gradient is not expected to be strong enough to produce=20
much blowing snow. By early Wednesday, snow could fall heavy at=20
times over central KS as favorable FGEN aligns with sufficient lift
into a potentially very deep DGZ and/or isothermal layer, but=20
these smaller scale features are hard to pinpoint this far out. In=20
addition, SLRs may be close to 20:1 or higher in these favorable=20
areas but otherwise waver around 15:1 given the colder air mass.=20
Northern edge of the precipitation shield has more uncertainty at=20
this point but a blend of the latest guidance offered a reasonable=20
starting point, with tapering amounts of snow into Nebraska. WPC=20 probabilities of at least 4 inches of snow are >50% over nearly all
of KS and focused along I-70 right into the Kansas City, MO area=20
as well (continuing into D4). Within this same region, lower=20
probabilities (10-50%) of at least 8 inches of snow are present.=20
Snowfall will expand rather quickly to the northeast toward the=20
Chicago metro by Wednesday afternoon/evening where WPC=20
probabilities=20

Southern side of the precipitation shield over OK and into the=20
Ozarks will likely be more marginal, and a mix or sleet and=20
freezing rain is likely due to the overrunning of the cold surface=20
with warmer air aloft. There, WPC probabilities of at least 0.10"=20
icing are low (10-30%).


...Pacific Coast...
Day 3...

Although still far out in time with limited confidence, it appears
the West will begin to become more active again mid-to-late week=20
as moisture begins to stream onshore from the Pacific. During D3,=20
there is considerable spread as to where the best moisture plume=20
will go as it gets restricted to the SW on the periphery of a large
trough over the CONUS and beneath a short-wavelength ridge over=20
the Pacific Northwest. At the same time, a deepening trough over=20
the Pacific will begin to track eastward, leading to a push of=20
moisture a bit farther NW and into southern/central CA. This could=20
result in some light to moderate snow reaching the Sierra before=20
00Z Thursday, but unquestionably more active weather with much=20
heavier snow will develop beyond this current forecast period. At=20
this time, WPC probabilities are moderate (30-50%) for 6+ inches in
the Sierra, generally above what could be very low snow levels of=20
2000-2500 ft.



Weiss/Fracasso




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!61kbvuEzGWlsYlaEQFrXiGBGJmhLa7oHs8PPWIGF-Op6J= v0Ajcdn6kgnNYYmmMQEZ3XmADzzHa8h4mqoDKUh_RAJ5-A$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!61kbvuEzGWlsYlaEQFrXiGBGJmhLa7oHs8PPWIGF-Op6J= v0Ajcdn6kgnNYYmmMQEZ3XmADzzHa8h4mqoDKUhvwKHBnE$=20

$$

=3D =3D =3D
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FOUS11 KWBC 160846
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EST Sun Feb 16 2025

Valid 12Z Sun Feb 16 2025 - 12Z Wed Feb 19 2025


...Great Lakes/Northeast...=20
Days 1-3...

A powerful multi-hazard winter storm will continue to push=20
into/through the Northeast today as the sharpening shortwave=20
beneath the 160kt jet exits the Midwest. Cold air over the=20
Northeast will eventually be scoured out nearly up to the Canadian=20
border as low pressure lifts from near PIT this morning to central=20
NYS this afternoon. By then, a new area of low pressure over Cape=20
Cod will start to become the dominant low and lift into the Gulf of
Maine as the old parent low weakens into western New England. The=20
new low will then move into Atlantic Canada tonight. The evolution=20
will favor all snow near the Canadian border and into interior=20
Maine where it will stay coldest thanks to the transfer of energy=20
to the coast, a transient mixed area of sleet/freezing rain to the=20
south, and rain surging northward after starting as snow this=20
morning farther south. Icing will hang on longer in the colder=20
terrain areas like the Adirondacks, Catskills, Berkshires/Greens,=20
and Worcester Hills/Monadnocks but also across coastal Maine on the
north side of the new area of low pressure. The low pressure=20
center will continue to deepen as it pulls away tonight into the=20
low 970s mb and the synoptic snow will end Monday morning.=20

WPC probabilities for at least 6 inches of snow today are highest=20
north of I-90 in NY, north of the MA/VT/NH border, and=20
north/northwest of I-95 through Maine. Totals near the Canadian=20
border and over northern Maine may eclipse a foot (probs 30-70%+).=20
Between the coast and I-90 or so, ice will be the main problem=20
before some areas change over, briefly, to a cold rain (esp the=20
valleys via strong southerly flow). WPC probabilities for at least=20
0.25" icing are highest (40-70%) in the Berkshires/southern Greens=20
and into the Worcester Hills/Monadnocks.

On the backside of the system, colder air will rush in across the=20
Great Lakes and into the central Appalachians, supporting lake=20
effect snow and upslope snow, respectively. Over eastern WV into=20
the MD Panhandle and the Laurel Highlands, upslope will provide for
modest snow totals with WPC probabilities of at least 4 inches=20

70%. Though that area will see snow ending on Monday, the lake=20

effect machine will keep cranking for the next few days as an upper
low swings through the region out of Canada. The flow will back=20
from NW to WNW and favor the typical lake belts, but especially=20
over the eastern U.P. of Michigan and southeast of Lake Ontario.=20
There, WPC probabilities for at least 8 inches of snow over the=20
next few days are high (>70%) and are moderate (40-70%) for 18=20
inches of snow in localized areas that remain under banding.=20



...Pacific Northwest/Rockies/Northern High Plains...
Days 1-3...

An active Pacific jet will guide a lead system into the Northwest=20
today, followed by onshore flow into Monday, then another system by
Tuesday into Wednesday. Snow levels will be a bit below pass level
and waver there for the next couple of days. East of the Divide a=20
very cold air mass will be in place thanks to high pressure over=20
Canada that pushes southward through the Plains, setting up upslope
flow into western MT. For the first system, Sun-Mon (though into=20
Tue over WY), the highest snow totals will be over the Cascades=20
eastward into the central Idaho ranges, western MT/WY and into=20
northern CO/southern WY. Several feet of snow are likely in the=20
higher terrain with only a brief break between systems. IVT values=20
exceeding the 90th percentile will move through the region today,=20
but then drop after tonight as the jet flattens out a bit.=20
Nevertheless, the nearly continuous terrain-enhanced snow will=20
accumulate well over 1-2 ft with WPC probs > 70% in the mountains.=20
Snow will be fairly heavy over western-central MT on the upslope=20
side as well, where WPC probs for at least 8 inches of snow are=20

50% around Billings up to Great Falls.=20

The next system will enter the PacNW D3 (Tues afternoon) with some
light snow for the Cascades. This will push eastward into D4.


...Central Plains/Mid-MS Valley/Mid-South...=20
Days 1-3...

Eastward extension of the Western US moisture will reach the=20
central Plains later this evening as WNW flow rushes through the=20
region. 700mb WAA will help drive light to modest snow across the=20
Black Hills southeastward into Nebraska overnight with fairly high=20
SLRs >15:1. Light snow will extend farther into northern MO by=20
early Monday before tapering off thereafter as the pattern shifts a
bit. WPC probabilities for at least 4 inches of snow D1-1.5 are=20
30-80% in this NW to SE stripe but diminish to <30% over northern=20
MO.=20

Overnight Mon into Tue, height falls will dig through the Four=20
Corners with a multi-stream jet east of 100W. A strong Arctic front
will push southward and increase low-level convergence, helping to
drive an expansion of snow through KS and into northern OK and=20
eastward, growing heavier as the shortwave aloft reaches the Plains
Tues evening. Heavy snow is expected to develop over eastern KS=20
into western MO beneath a quickening upper jet east of the=20
Mississippi, bleeding southward into northern/northeastern OK and=20
northern AR overnight. By the end of the period, the shortwave will
continue into the Mid-South with light to moderate snow into TN.=20
On the southern side of the precip shield, colder air at the=20
surface will undercut the milder >0C thermals aloft over central AR
where freezing rain is likely to form (with some sleet to the=20
north).=20

WPC probabilities for at least 4 inches of snow are >50% from=20
northwestern KS eastward to southern IL/western KY/northwestern TN,
including northern OK/AR. Within this broad region, an axis of=20
heavier snow is likely to develop with rates >1"/hr and snow totals

8". WPC probabilities for at least 8" are >50% over southeastern=20

KS and southern MO. Farther south, ice probs for at least 0.10" are

30% around the Ouachita Mountains.=20

Fracasso


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4AZw-ucawhkep6Z6Gn1ZandzoOVlwTL2kJqJJdio1FJHQ= 7BS2cc3thylAk2S-6orJQfQ1EdnbZkzg86Q7WqlfzYEiOs$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!4AZw-ucawhkep6Z6Gn1ZandzoOVlwTL2kJqJJdio1FJHQ= 7BS2cc3thylAk2S-6orJQfQ1EdnbZkzg86Q7Wqlj-uEOzY$=20

$$

=3D =3D =3D
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FOUS11 KWBC 152003
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 PM EST Sat Feb 15 2025

Valid 12Z Sat Feb 15 2025 - 12Z Tue Feb 18 2025


...Corn Belt/Midwest/Great Lakes/Northeast...=20
Days 1-3...

A dynamic storm system, forecast to produce a myriad of weather
related hazards over the next 48 hours, will gather strength over
the Mid-South this afternoon and rapidly intensify as it tracks
northeast through the northeastern U.S. on Sunday. The current
areas of wintry weather affecting the Great Lakes and Northeast are
largely due to 850-700mb WAA and 300K isentropic ascent into an
air-mass that is sufficiently cold enough to produce snow from the
northern Great Lakes to the Northeast. A little farther south,
lingering CAD in place over the northern Mid-Atlantic will be ripe
for a wintry mix of sleet and freezing rain this afternoon and this
evening. By 00Z this evening, the surface low tracking into the
Ohio Valley will begin to deepen rapidly as the 500mb trough aloft
sharpens and the divergent right-entrance region of a >175kt 200mb
jet streak maximizes upper level ascent. 850-700mb WAA will=20
increase over the Northeast, as will an IVT along the East Coast=20
Sunday morning that exceeds an impressive 1,500 kg/m/s. According
to NAEFS, these values would surpass all observed IVT values for=20
this time of year according to the CFSR climatology (1979-2009).=20
Some of this moisture will wrap around the strengthening 850mb low=20
in the in the Ohio Valley Sunday morning and result in a period of=20
heavy snowfall from the Lower Ohio Valley on north and east through
eastern IN, northern OH, and western NY through Sunday afternoon.

Over the Northeast, a banana-shaped area of high pressure will act
to reinforce the CAD signature over New England and the northern=20 Appalachians. This means despite the growing >0C warm nose at low-
levels aloft, surface temperatures will remain below freezing long
enough to support a lengthy period of freezing rains. This is the
case primarily in the Poconos, Adirondacks, Berkshires, Worcester
Hills, Green and White Mountains, and across southern Maine. The
latter is particularly prone to significant ice accumulations given
surface temperatures will struggle to top the mid 20s through
Sunday evening. Some of the heavier rates may limit ice
accumulations to some extent, but given the exceptionally cold
surface-925mb temperatures in place, expect ice to still accumulate
at a healthy clip Sunday afternoon in New England. By 00Z Monday,
the storm is forecast to be in the low 970mb range with strong
winds bringing about additional hazards from the Great Lakes to the
Northeast. In the Great Lakes, strong CAA will support numerous
lake-effect snow (LES) showers from the Michigan U.P. to the=20
eastern Great Lakes. Farther south, NWrly flow with ~40kt 850 mb=20
winds (above the 90th climatological percentile via NAEFS) will=20
also produce upslope snow enhancement along the spine of the=20
Central Appalachians through Monday morning. Lastly, for trees and=20
power lines that have lingering heavy icing in the Northeast,=20
strong winds will only add further stress to trees and power lines
and could exacerbate the potential for downed trees and power=20
outages.=20

The worst impacts of this event are likely to be felt in the
Northeast where the combination of heavy snow, significant icing,
and strong winds will make for dangerous to even impossible travel
conditions, along with the growing concern for numerous power
outages and downed trees. WPC probabilities show moderate-to-high
chances (50-70%) for >0.25" of ice accumulation in the Catskills
and Berkshires. Similar probabilistic guidance exists for >8" of=20
snowfall in the Adirondacks, Green, and White Mountains, as well as
much of northern Maine. Farther west, there are moderate chances=20
(40-60%) for >6" of snow from eastern Michigan on south to=20
northeast IN and northwest OH. As the storm departs, LES will cause
locally heavy snowfall to occur along the Michigan U.P. and along=20
the Tug Hill in northern NY. The Tug Hill in particular has=20
moderate-to-high chances (50-70%) for snowfall totals >8" through=20
Monday night. With very cold temperatures pouring in in wake of the
storm, expect LES to continue over the Tug Hill into Tuesday with=20
any lingering snowpack sticking around through mid-week.


...Pacific Northwest/Rockies/Northern High Plains...
Days 1-3...

An active Pacific jet stream pattern will direct a stream of mid-
upper level moisture into the northwestern U.S. tonight, through
Sunday, and through Monday. A series of 500mb disturbances embedded
ejecting out of the base of a longwave upper trough in the
northeast Pacific will provide upper-level ascent from the Pacific
Northwest to the Northern Rockies through Monday as well.=20
Snow levels in the Olympics and WA Cascades will drop to as low as
2,500ft today but rise to above 3,000ft by Sunday. Snow will pick
up in intensity Saturday night and through Sunday in the OR
Cascades, as well as the Blue, Sawtooth, Bitterroot, Absaroka, and
Tetons. This active jet stream pattern will also direct an
anomalous IVT well inland across the central Rockies. NAEFS shows

200 kg/m/s IVT stretching from the CA coast to the Front Range of

the Central Rockies Sunday afternoon and through Monday morning (values
that are well above the 90th climatological percentile). This will
support periods of heavy snow in the Bear River, Uinta, Wasatch,=20
and Rockies of southern WY and western CO. Snow will peak in
intensity across these ranges on Monday and gradually taper off on
Tuesday as a pair of upper level troughs (one in eastern Montana,
the other in the Southwest) track south and east, allowing for more
subsidence and a reduction in moisture to ensue. As much as 1-2
feet of snow are expected across many of these aforementioned
mountain ranges, although the WA/OR Cascades, Blue, Bitterroot,
Teton, and CO/southern WY Rockies are the ranges that could see
localized totals approach 3 feet between this afternoon and Tuesday
afternoon.

Farther east, the active jet stream and persistent stream of
Pacific moisture will track across the High Plains of Montana and
into mountain ranges such as the Big Snowy, Little Belt, and Lewis
Range. However, adding to the heavy snow potential is the placement
of strong high pressure of southern Canada (NAEFS shows >1040mb=20
high with >97.5 climatological percentiles present) and low
pressure over the the Pacific Northwest will support SErly low-
level upslope flow into these ranges starting Saturday night and
lasting through early Tuesday. While precipitation amounts and
rates will be moderate for the most part, high SLRs of 16-19:1 will
make use of the available precipitation and produce dry/efficient
snowfall over the region. The forecast calls for anywhere from
8-14" in the central Montana, which includes Billings and Great=20
Falls. In the Big Snowy, Little Belt, Lewis Range, and even as
south as the Big Horns, 1-2 feet of snow is forecast with some
of the peaks seeing as much as 30" through Tuesday.=20


...Central Plains...
Days 2-3...

The same anomalous IVT that is aiding in the heavy mountain snow in
the Rockies will also accompany a period of 700mb WAA that allows
for a stripe of moderate-to-heavy snow from the Black Hills and
eastern WY through central NE through Monday morning. The band of
snow will stretch as far east as the IA/MO border through Monday
morning before a brief break in the moderate snowfall arrives
Monday afternoon. By Monday night, one of the shortwave troughs
entering the Central Rockies will gradually deepen while upper-
level diffluence increases at the nose of a 250mb jet streak
rounding the base of the trough. By Tuesday morning, that
aforementioned 250mb jet streak will co-locate it's divergent
left-exit region the divergent right-entrance region of the 250mb
jet over the eastern U.S.. Periods of heavy snow will break out to
the north of the mean 850-700mb FGEN axis over eastern OK and
northern AR on Tuesday, although not all guidance is in agreement=20
with a good consensus on both totals and where the heaviest=20
snowfall occurs. That said, the setup favors heavy snow and=20
potentially significant ice accumulations given the favorable=20
synoptic-scale lift and strong WAA aloft overrunning a very cold=20
air-mass that will be anchored by a frigid Canadian high pressure=20
system to the north.=20

At the moment, WPC probabilities paint moderate-to-high chances=20
(50-70%) for snowfall totals >6" from central and eastern KS to=20
south- central MO through Tuesday afternoon. There is the potential
for disruptive ice accumulations from eastern OK on east to the=20
Ozarks of northern AR and southern MO as well. WPC's Probabilistic=20
WSSI shows high chances (>70%) for Moderate Impacts (disruptions=20
to daily life; hazardous driving conditions and closures) in the=20
areas mentioned above for snowfall, although there could very well=20
be treacherous travel conditions from eastern OK to the Ozarks due=20
to accumulating ice. This forecast remains fluid, so continue to=20
check in for the latest forecast information from your local=20
weather forecast office.=20

Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!96rLQ7GiGebg9WNbVMen3cDVuUCrWBgEBWdHsZXTb24Gm= CDeaG_9JZylW4kT0RiMNgtJwB0BNltmB9DjHZtBdicIBYc$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!96rLQ7GiGebg9WNbVMen3cDVuUCrWBgEBWdHsZXTb24Gm= CDeaG_9JZylW4kT0RiMNgtJwB0BNltmB9DjHZtBTJH9HRY$=20

$$

=3D =3D =3D
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FOUS11 KWBC 162015
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
315 PM EST Sun Feb 16 2025

Valid 12Z Sun Feb 16 2025 - 12Z Wed Feb 19 2025


...Great Lakes/Northeast...=20
Days 1-2...

A dynamic winter storm is unfolding today with heavy snow across
northern Maine, while a protruding warm nose of >0C air at low
levels causes precipitation to fall in the form of sleet and/or
freezing rain from central Maine and the northern Appalachians to
the Maine coast. WPC's Snowband Probability Tracker shows the HREF
guidance suite has members that are producing as much as 1-2"/hr
snowfall rates across northern Maine through this evening. Heavy
snow is expected in parts of NY's North Country this evening, and=20
on the western flank of the storm as it tracks into Maine tonight.=20
WPC probabilities show high chances (>70%) for snowfall >8" in the=20
North Woods, Central Aroostook, and St. John Valley, with the=20
latter of the three having high chances (>70%) for over a foot of=20
snow. A couple additional inches of snow are possible in the=20
Adirondacks and the rest of VT as the storm pulls away. Meanwhile,=20
soundings will be more supportive of freezing rain and sleet=20
farther south with another tenth to a quarter inch of ice expected=20
from southern and central NH/VT on east through the southern tier=20
of Maine. Strong wind gusts topping 50 mph could add further stress
to trees and power lines with heavy/wet snow or ice, keeping the=20
potential for additional power outages and tree damage as a=20
potential impact through Monday morning.=20

On the backside of the winter storm, much colder air races across=20
the Great Lakes and into the central Appalachians, giving rise to=20
lake effect snow bands and upslope snow in these regions. For
the Potomac Highlands of eastern WV on north to the Laurel=20
Highlands, upslope flow will generate locally heavy snow totals=20
with WPC probabilities sporting moderate-to-high chances (50-70%)
for >6" in these mountain ranges. Snow will taper off in the
central Appalachians by midday Monday, while the lake effect snow
machine looks to keep producing bands of heavy snow through Tuesday=20
as an upper low heads for the eastern Canadian Maritime and an
elongated 500mb trough axis moves in overhead. Low level flow=20
backs from NW to WNW and favor the typical lake belts, but most=20
notably over the eastern U.P. of Michigan and southeast of Lake=20
Ontario. WPC probabilities for at least 8" of snow over the next=20
few days are high (>70%) and are moderate-to-high (50-70%) for 18=20
inches of snow downwind of Lake Ontario.


...Pacific Northwest/Rockies/Northern High Plains...
Days 1-3...

An active Pacific jet will direct a storm system and its associated
IVT to the south of the storm into the Northwestern U.S. through
Monday, followed by another system by Tuesday into Wednesday. Snow
levels will dip just below pass level and oscillate there through
Monday night. East of the Continental Divide a very cold air mass=20
will be in place thanks to high pressure over Canada that pushes=20
southward through the Plains, setting up upslope flow into western=20
MT. For the first system, Sun-Mon (though into Tue over WY), the=20
highest snow totals will be over the Cascades eastward into the=20
central Idaho ranges, western MT/WY and into northern CO/southern=20
WY. Several feet of snow are likely in the higher terrain with only
a brief break between systems. IVT values exceeding the 90th=20
percentile will move through the region today, but then drop after=20
tonight as the jet flattens out. Nevertheless, the nearly=20
continuous terrain- enhanced snow will accumulate well over 1-2 ft=20
with WPC probs > 70% in the mountains. Snow will be fairly heavy=20
over western-central MT on the upslope side as well, where WPC=20
probs for at least 8" of snow are >50% around Billings up to Great=20
Falls.=20

The next system will enter the Pacific Northwest starting Tuesday
Night with some periods of snow for the Cascades. Snow will then
extend into the Northern Rockies throughout the day on Wednesday.
WPC probabilities shows moderate-to-high chances (50-70%) for >6"
of snowfall for the Cascades, Blue, and Sawtooth mountain ranges.


...Central Plains/Mid-MS Valley/Mid-South...=20
Days 1-3...

The anomalous IVT responsible for periods of heavy snow in the=20
Rockies will accompany a period of 700mb WAA over the Central=20
Plains. The combination of 700mb FGEN and an accelerating 250mb=20
jet aloft will support a stripe of moderate snow from the Black
Hills on south and eats through NE and into the Lower Missouri
River Valley tonight and into Monday. This band eventually weakens
to where mainly light snow is expected in these areas through
Monday afternoon. By Monday night, the stronger 500mb shortwave
trough tracking across the Central Rockies will gradually deepen
while upper-level diffluence increases at the nose of a 250mb jet=20
streak rounding the base of the Central Rockies trough. By early=20
Tuesday morning, the aforementioned jet streak will co-locate its=20
divergent left-exit region with the divergent right-entrance=20
region of a strengthening jet streak over the eastern U.S.. As=20
southerly and moist 850mb winds increase over Texas and low-level=20
WAA results in 850mb FGEN from the OK/TX Panhandles to as far east=20
as the Ozarks and Ouachita Mountains, periods of heavy snow will=20
envelope these regions with deteriorating travel conditions=20
throughout the day.=20

There are still some different scenarios on guidance as to where=20
and how long the heaviest bands of snow take shape. WPC
probabilities are keying in on southeast KS, southern MO, and as=20
far east as the Mississippi River bordering southeast MO and=20
western KY as most likely to witness heavy snow where there are=20
high chances (>70%) for snowfall amounts topping 6". In fact, there
are low-to-moderate chances (30-50%) in southern MO for >12" of=20
snowfall. Farther south across northern OK, northern AR, and=20
northwest TN, a disruptive blend of snow and ice would make for=20
treacherous travel conditions Tuesday and continuing into Tuesday=20
night. As the storm tracks east into the Mid-South on Wednesday,=20
heavy snow will blanket areas from the OH-MS River Confluence on=20
east into the Ohio Valley. WPC probabilities do depict moderate=20
chances (40-60%) for snowfall totals >4" in these areas. For ice=20 accumulations, the Ouachita Mountains sport low-to-moderate chances
(30-50%) for ice accumulations >0.1" through Wednesday morning.=20
WPC's WSSI-P shows low-to-moderate chances (30-50%) for Major=20
Impacts (dangerous or impossible travel conditions; widespread=20
closures and disruptions) for northeast OK, southeast KS, southern=20
MO, and far northern AR. As high as 60% chances exist for Moderate=20
Impacts (hazardous driving conditions; some closures and=20
disruptions) stretch as far west as Wichita and the I-35 corridor=20
on east to northern TN and western KY.

...Central Appalachians/Mid-Atlantic...
Day 3...

As the upper-level trough driving the Mid-South storm system tracks
east on Wednesday, modest PVA aloft combined with 850-700mb WAA
will direct the shield of heavy snow in the Mid-South towards the
Appalachians and Mid-Atlantic. What guidance largely agrees upon is
the southern stream storm system tracking ENE towards the Southeast
coast Wednesday afternoon and steadily strengthening beneath the
divergent right-entrance region of a strengthening 140kt 250mb jet
streak to the north. There is an anomalous IVT topping 500 kg/m/s
over the Southeast that will help direct plenty of moisture into=20
the southern Mid-Atlantic. As 850-700mb FGEN occurs over southern
VA, bands of heavy snow should take shape and lead to hazardous
travel conditions from southwest VA and the central Appalachians=20
of WV and western VA to the VA Tidewater Wednesday afternoon.=20

Probabilistic guidance is suggesting an area from eastern KY and=20
the WV/western VA Appalachians to the DelMarVa Peninsula as having=20
the best odds of seeing heavy snow. WPC probabilities show a=20
growing area of moderate-to-high chance probabilities (50-70%) for
snowfall >4" in southwest VA through Wednesday evening, with heavy
snow spreading across southern VA and the DelMarVa Peninsula by=20
Wednesday evening. With the storm also deepening as it reaches the=20
coast Wednesday night, blowing snow and heavy snowfall rates of=20
1-2"/hr would cause near whiteout conditions, especially for the=20
DelMarVa Peninsula. There is also the concern for significant icing
as WPC probabilities show moderate-to-high chances (50-70%) for=20

0.01" of ice over central NC and north-central SC. These areas=20

would be most at risk for treacherous driving conditions on=20
Wednesday.

However, 500mb skewness plots continue to show some subtle=20
difference in the depth/strength of the large upper low over the=20
Midwest and how it interacts with the lead shortwave trough in the=20 Southeast. Farther southeast, while not as pronounced there are=20
also lingering discrepancies in the depth/speed of the lead trough
in the Southeast as well. While most ensemble guidance has started
to come into focus with southern VA and the DelMarVa Peninsula=20
being most favored for heavy snow, a deeper/more phased upper-
level pattern would allow for heavy snow to creep northward up=20
I-95 and get closer to the major metro centers of Washington D.C. and Baltimore. There are also some solutions that show the lead=20
shortwave could be flatter as well, and make northern NC and far=20
southeast VA the focus for heavy snow. Residents in the Mid-
Atlantic should keep a close eye on the forecast as any subtle
adjustment in speed/timing/phasing of these atmospheric variables
could mean 50-100 mile shifts in where the heavy snowfall axis sets
up.


Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-ZoJKdSTM0rtBdKVKAsgGJqkg_h4PrpvucnwYCtuDzsBq= O-QkTOyCqteq1A3C4I2ImzcUSU3iBYCpbVwB4luOkqaL60$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-ZoJKdSTM0rtBdKVKAsgGJqkg_h4PrpvucnwYCtuDzsBq= O-QkTOyCqteq1A3C4I2ImzcUSU3iBYCpbVwB4luwwI2AJs$=20

$$

=3D =3D =3D
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FOUS11 KWBC 100843
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 AM EST Mon Feb 10 2025

Valid 12Z Mon Feb 10 2025 - 12Z Thu Feb 13 2025

...Great Lakes...
Days 1-2...

Large surface high pressure stretching from the northern Plains
through Mid-Atlantic creates enough of a pressure gradient across
the Great Lakes to promote continuing westerly 850mb wind up to 35
kts at times thanks to a couple passing shortwaves. The first=20
shortwave is racing across the Great Lakes and New England this=20
morning with a third impulse speeding across the region Tuesday=20
morning as flat/progressive flow persists across the CONUS. Each of
these subsequent shortwaves will be accompanied by a weak cold=20
front, driving enhanced CAA across the Great Lakes to support=20
periods of lake effect snow (LES). On D1, 850mb temps fall to -15C=20
or more, steepening low-level lapse rates sufficiently to lift=20
inversion levels to nearly 10,000 ft, which with ascent maximizing=20
into the lowering DGZ will cause bands of heavy snow with rates of=20
1"/hr or more across the U.P. of MI, as well as SE of Lake Ontario=20
and into the northern Finger Lakes region early D1 before flow=20
shifts more westerly into the Tug Hill by tonight. WPC=20
probabilities D1 are moderate (40-60%) for 6+ inches along the SE=20
lake shore of Ontario and Tug Hill, as well as across the Keweenaw
Peninsula of the U.P. of MI.


...Mid-Mississippi Valley to the Mid-Atlantic...=20
Days 2-3...

Confluent mid-level pattern will maintain progressive flow across=20
the CONUS as the next in this parade of storms develops over the=20
Central Plains and Ozarks Monday evening. This system will=20
strengthen in response to vorticity energy shedding from the base=20
of a longwave trough initially over Baja, combining with the RRQ of
a southern stream jet streak which begins to amplify and arc=20
meridionally, leaving favorable diffluence atop the mid-level=20 PVA/divergence. The downstream confluence of the northern and=20
southern streams should result in suppression of this wave, keeping
it fast and generally flat from west to east, but will also result
in significant ascent and a prolonged period of precipitation as=20
isentropic ascent from the Gulf surges northward and spokes of=20
vorticity continue to lag back to the SW leaving a long duration of
ascent.

The north-south trends with this system appear to have stabilized
as most upper features settle into place with only subtle changes=20
in the forecast expected at this point. This aims the heaviest=20
axis of overlapping QPF and subfreezing thermals from northeast KY,
through central VA into the Delmarva.=20

Based on current guidance, this is beginning to look like a=20
significant winter event containing snow and sleet and freezing=20
rain, generally from the Ozarks almost due east into the Central=20 Appalachians and the I-95 corridor from Richmond, VA to Baltimore,=20
MD. The downstream confluence of the mid-level pattern will force=20
this generally west-to-east axis of heavy precipitation, with=20
290-295K isentropic ascent and accompanying WAA fueling the=20
elevated PWs progged by NAEFS to exceed the 90th climatological=20
percentile as far north as the TN VLY and southern Mid-Atlantic=20
(NC/VA border). This will supply plentiful moisture for heavy=20
precipitation, and the sharpening baroclinicity on the WAA leading=20
to impressive 850-700mb fgen will help to concurrently enhance=20
ascent. This suggests that precipitation rates will be heavy at=20
times, although in areas with snow the DGZ appears elevated and the
best fgen is well below that, which when combined with modestly=20
"warm" temperatures should keep SLRs low and this could be a heavy=20
and wet snow for most of the area. The end of the latest 00z HREF
depicts the potential for snowfall rates up to 1"/hr in the
heaviest band. Current WPC probabilities are high (>70%) in=20
northeast KY, the central Appalachians, central VA into southern MD
and the central Delmarva D2 for 4+ inches of snow. Medium probs=20
(40-70%) expand northward through northern VA, MD, DE, and southern
NJ, with a very tight gradient expected along the northern and=20
southern fringes. This places the highest potential for significant
snow between Richmond, VA and Washington, D.C.

Farther to the south, there is likely to be a transition zone from
rain to snow which will include axes of moderate to heavy freezing
rain, especially in the higher elevations around the Ozarks, as=20
well as across portions of the Central Appalachians from eastern KY
through SW VA. There remains a lot of uncertainty as to the=20
amounts of icing, especially noting that rates could be heavy at=20
times which don't efficiently accrete, and with the general=20
synoptic uncertainty continuing, but there is high confidence=20

70%) for warning-level icing (above 0.25") of ice in SW VA, with=20

locally as much as 0.6" of damaging ice possible through Thursday
morning.

As vorticity lobes continue to shed eastward from the Baja trough,
and as the developing full latitude trough (merging northern and=20
southern streams over the Intermountain West) lags the first=20
impulse, a second system with additional precipitation will=20
approach this same area from the SW late D3 /Wednesday aftn./ This=20
will again produce an axis of all p-types from the Ozarks eastward=20
to the Mid-Atlantic, and its possible in some areas there will not=20
even be much of a break before this second impulse. The Wednesday=20
system developing in the Central Plains will likely be more intense
with respect to the surface feature and crossing west of the
Appalachians, so more warm air should flood northward downstream,=20
but the evolution of this second wave will be somewhat dependent on
the track of the first event. At this time, WPC probabilities for=20
0.1" of freezing rain D3 generally just feature patch 10-30% from=20
the Ozarks into northern KY.


...Central Rockies/Plains/Midwest/Great Lakes...=20
Days 2-3...

As the longwave trough over the West passes the Rockies Tuesday=20
into Wednesday, precipitation will expand across the central=20
Plains. Snow over the Rockies will accumulate several inches=20
Tuesday afternoon and overnight through early Wednesday over the=20
Medicine Bow mountains with at least 6 inches above 10,000ft likely
(probs >50%). Positive tilt and broad SW flow will favor a=20
progressive system D3, but the potential exists for moderate to=20
heavy snow across much of Kansas Tuesday night into Wednesday.=20
Upper jet will extend from TX northeastward to the Midwest with=20
speed divergence over the Plains helping to promote ascent into a=20
moistening column on WAA from the south in the lower levels. A=20
large high pressure to the north will supply NE winds to the region
but the gradient is not expected to be strong enough to produce=20
much blowing snow. By early Wednesday, snow could fall heavy at=20
times over central KS as favorable FGEN aligns with sufficient lift
into a potentially very deep DGZ and/or isothermal layer, but=20
these smaller scale features are hard to pinpoint this far out. In=20
addition, SLRs may be close to 20:1 or higher in these favorable=20
areas but otherwise waver around 15:1 given the colder air mass.
Dry air is always a concern along northern areas of the
precipitation shield, but the duel jet structure developing over
the central U.S. and a broad moist forecast in upper air relative=20
humidity fields, the greatest uncertainty will likely be associated
with localized forcing and banding potential.

By Wednesday night, the system begins to further organize and pick
up forward speed as the surface low lifts through the Ohio and
Tennessee valleys. Snow is expected to expand from southern IA and northern/central MO through much of IL, southern WI, northern IN,
and the L.P. of Michigan. A narrow corridor of mixed ptype is also
still expected somewhere from southwest MO through southern IL and
into southern IN and western OH. The event will quickly conclude=20
by the end of D3 across the Midwest as CAA and dry air rushes into=20
the region. However, increasing WAA will begin to spread snow,=20
sleet, and freezing rain northward across the Lower Great Lakes and
Northeast by early Thursday.

WPC probabilities of at least 4 inches of snow for this large
system are >50% from far eastern CO across much of KS, southern=20
NE, northern MO, southern IA, central/northern IL, southern WI,=20
northern IN, and much of the L.P. of MI. This includes cities such=20
as Kansas City, Des Moines, Chicago, and Milwaukee just to name a=20
few. Within these probabilities, 20-50% chances for at least 8=20
inches of snow follow along and just north of I-70 in KS and span=20 east-northeast across the Midwest towards lower Michigan. Maximum
snowfall amounts of 8 to 12 inches appear most likely. Southern=20
side of the precipitation shield over OK and into the Ozarks will=20
likely be more marginal, and a mix or sleet and freezing rain is=20
likely due to the overrunning of the cold surface with warmer air=20
aloft. There, WPC probabilities of at least 0.10" icing are low=20
(10-30%).


...Pacific Coast...
Day 3...

Although still far out in time with limited confidence and
extending into Day 4, it appears the West will begin to become=20
more active again mid- to- late week as moisture begins to stream=20
onshore from the Pacific. During D3, there remains noticeable=20
spread as to where the best moisture plume will go (GEFS quicker=20
and north compared to the ECENS) as it gets restricted to the SW on
the periphery of a large trough over the CONUS and beneath a=20
short- wavelength ridge over the Pacific Northwest. At the same=20
time, a deepening trough over the Pacific will begin to track=20
eastward, leading to a push of moisture a bit farther NW and into=20 southern/central CA. This could result in some light to moderate=20
snow reaching the Sierra before 00Z Thursday, but unquestionably=20
more active weather with much heavier snow will develop beyond this
current forecast period. At this time, WPC probabilities are=20
moderate (30-60%) for 6+ inches in the Sierra, generally above what
could be very low snow levels of 2000-2500 ft.



Snell/Weiss/Fracasso





...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!6sh-UaRhzxHisyvxXE6Nyb82OnQUvy0HI6iIP_OSc-pXp= O0QEd-mh5xIh5RnTwTBc2K-lWu0rz8VfaUvrMZTpBDucpw$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!6sh-UaRhzxHisyvxXE6Nyb82OnQUvy0HI6iIP_OSc-pXp= O0QEd-mh5xIh5RnTwTBc2K-lWu0rz8VfaUvrMZTPQixzH0$=20

$$

=3D =3D =3D
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FOUS11 KWBC 102048
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 PM EST Mon Feb 10 2025

Valid 12Z Mon Feb 10 2025 - 12Z Thu Feb 13 2025

...Great Lakes...
Day 1...

A strong cold front will exit into New England Tuesday morning,=20
leaving strong CAA across the Great Lakes in its wake. 850mb temps=20 plummeting to -15C to -20C, coldest over Lake Superior, will=20
support a renewed period of lake effect snow (LES) in the favored=20
W/NW snow belts across the U.P. of MI and into the Tug Hill=20
Plateau. A very cold column over Lake Superior will drive the DGZ=20
down to the surface which will allow for a maximum intersection of=20 lake-induced ascent and the snow growth region. Farther east across
Lake Ontario, the overlap won't be quite as efficient, but some=20
higher moisture due to an upstream connection will additionally=20
enhance the LES potential. Snowfall rates of 1"/hr or more are=20
likely Monday night and Tuesday before subtle height rises bring an
end to LES before D2. WPC probabilities for 6+ inches are above=20
70% in the Tug Hill Plateau and portions of the eastern U.P. near=20
Whitefish Pt on D1.


...Mid-Mississippi Valley to the Mid-Atlantic...=20
Days 1-3...

Active pattern continues with two significant winter weather=20
events progged to impact the area with different hazards through=20
the week.

The first begins early Tuesday morning as precipitation begins to=20
expand across the Ozarks, Mid-Mississippi Valley, and Tennessee=20
Valley. This precipitation will be the result of an overlap of=20
forcing and moisture expanding into the region from the west and=20
south. A shortwave trough and accompanying vorticity maxima will=20
eject from the Four Corners this evening and race eastward into the
Southern Plains by Tuesday morning as it weakens in response to=20 confluent/flat flow across the eastern CONUS. Despite the modest=20
amplitude of this feature, ascent will intensify through modest PVA
and mid-level divergence overlapped with the right entrance region
to a jet streak amplifying to the northeast. A weak surface wave=20
may develop and skirt almost due east accompanying this system, but
in general precipitation will be driven by the overlap of the=20
synoptic ascent and increasingly impressive moist isentropic=20
upglide/WAA emerging from the Gulf of Mexico.

The moisture surging northward will be significant as reflected by
mixing ratios within the robust 290-295K isentropic ascent=20
reaching as high as 6-8 g/kg, drawing PWs as high as the 90th=20
climatological percentile as far north as VA/KY. This will an=20
expanding swath of precipitation, with rounds of heavier rates=20
likely embedded. The guidance has generally started to stabilize=20
the footprint and thermal structure, but some wavering is still=20
possible especially the upstream shortwave intensity and speed=20
continues to fluctuate. However, there is high confidence that a=20
stripe of heavy snow will spread east from Kentucky through=20
Delaware. Snowfall rates of 1+"/hr are likely at times, especially=20
within a west-to-east oriented fgen band progged to setup from=20
eastern KY into DE, where 850-700mb fgen maximizes ascent and=20
occurs in conjunction with CSS (EPV* < 0.25) to support CSI. Where=20
this band develops, locally higher amounts of snow are possible,=20
but in general WPC probabilities spanning D1 and D2 are high (>70%)
for more than 4" from eastern KY though the Central Appalachians=20
eastward near Washington, D.C. and into southern DE. Locally more=20
than 8 inches is possible where the most intense band tracks.

Farther to the south, a transition zone is still expected where a=20
mixture of snow, sleet, and freezing rain will occur. This is most=20
likely from the Ozarks, through KY and into the Central=20
Appalachians, especially along the Blue Ridge of NC/VA. While some=20
sleet is possible, the predominant mixed p-type is likely to be=20
freezing rain within this axis, and will almost certainly be=20
significant (to locally damaging) in the vicinity of the Blue=20
Ridge. WPC probabilities for more than 0.25" are above 70% in the=20
vicinity of the Blue Ridge where locally more than 0.5" is possible
(30% chance). This will cause severe impacts including power=20
outages, scattered tree damage, and dangerous travel. Surrounding=20
this, WPC probabilities for more than 0.1" of 10-30% encompass a=20
much larger area including the Ozarks, parts of Kentucky, and the=20
Central Appalachians near the MD Panhandle and Laurel Highlands.

This first event winds down late Wednesday morning through the=20
afternoon /D2/, but just as the column begins to dry aloft, renewed
WAA ahead of the next system approaches within this progressive=20
pattern. While the DGZ dries out across the Mid-=20
Atlantic/Appalachians, the low levels re-saturate, and it is=20
possible in some areas there is never a break in wintry=20
precipitation due to very light snow/snow grains/freezing drizzle=20
Wednesday. Eventually the column re-saturates though as a more=20
intense low pressure developing over the Southern Plains lifts=20
northeast into the Ohio Valley with another round of mixed=20
precipitation spread into the region.

This second wave will be stronger, but also farther inland, so=20
many areas will begin with snow or freezing rain and eventually=20
transition to all rain. The heaviest precipitation will likely=20
begin right around the end of D2 in the Central Appalachians and=20
then expand northeast into the Mid-Atlantic around 00Z/Thursday or=20
slightly afterwards. High pressure wedging into the region will=20
again force impressive isentropic overrunning, and locations from=20
northern VA through PA will likely begin as a burst of moderate=20
snowfall before quickly transitioning to sleet, freezing rain, and=20 eventually all rain before waning Thursday evening. The heaviest=20
snowfall is likely in the Poconos where WPC probabilities for 2+=20
inches are as high as 50%, with icing exceeding 0.1" possible=20

30%) in the Laurel Highlands and parts of the Poconos.

...Central Rockies/Plains/Midwest/Great Lakes...=20
Days 1-3...

Troughing over the PacNW/BC this evening will dip into the Great=20
Basin and into the central Rockies tomorrow evening, with broad WSW
flow across CO. This will favor an expansion of snowfall over the=20
Medicine Bow mountains and into the San Juans/Sangre de Cristos=20
where upslope enhancement will wring out several inches of snow=20
area-wide. For the D1.5 period, WPC probabilities for at least 6=20
inches of snow are >50% above 10,000ft or so.=20

By Wednesday morning, troughing will pass the spine of the Rockies
as low-level moisture increases over the foothills to the Plains=20
via SE to E flow. This will combine with NE flow at the surface to=20
increase snow into the Front Range, though snow should generally be
light overall. WPC probabilities for at least 4 inches are near=20
30% over parts of the I-25 corridor.=20

The more intense snowfall will manifest farther east over Kansas=20
starting late Tuesday into Wednesday. There, the potential exists=20
for moderate to heavy snow across much of Kansas as the upper jet=20
extends from TX northeastward to the Midwest. Combination of WAA,=20
tightening thermal gradient (increasing FGEN), and favorable/deep=20 DGZ/isothermal layer will promote locally heavy snow with >1"/hr=20
rates (per WPC snowband tool). A large high pressure to the north=20
will supply NE winds to the region but the gradient is not expected
to be strong enough to produce much blowing snow even as low=20
pressure deepens over the ArkLaTex. SLRs may eclipse 20:1 in the=20
most favorable bands but otherwise hover close to 15:1 along the=20
I-70 corridor from GLD to MCI. Trend in the recent guidance has=20
been a bit to the N/NW especially east of the Plains, which may=20
bring more ice into southeastern KS than what was seen 24 hours=20
ago. There, overrunning will favor sleet and freezing rain from SW=20
to NE from OKC to southeastern KS into southern MO. WPC=20
probabilities for at least 0.1" ice are low-moderate in this region
(10-50%). For snowfall, PVA and FGEN will force much of the=20
precipitation in advance of the trough with the axis of heavier=20
snowfall along I-70 toward/into Kansas City, then extending=20
northeastward. WPC probabilities for at least 4 inches of snow are=20
high (>70%) over most of central/northern KS into southern NE with=20
some probs (30-50%) for at least 8 inches.

By Wednesday night, the system begins to further organize and pick
up forward speed as the surface low lifts through the Ohio and=20
Tennessee valleys. Snow is expected to expand from southern IA and=20 northern/central MO through much of IL, southern WI, northern IN,=20
and the L.P. of Michigan. A narrow corridor of mixed ptype is also=20
forecast in a southwest to northeast band from southern MO through=20
central IN and northwestern OH. Here, the NW trend in the 12Z=20
guidance was more pronounced (esp the 12Z NAM), and WPC made a=20
modest adjustment to the NW given other signals from other=20
models/ensembles (which were not as dramatic or not shown at all).=20
SLRs should increase to the NW deeper into the colder column, but=20
pared back the NBM which could be a bit too high. Nevertheless,=20
combination of strong PVA and lower level FGEN into a deep DGZ=20
should provide for an axis of heavier snow, but where that=20
materializes is bit fuzzy (including any lake enhancement off Lake=20
Michigan on NE winds).=20

Right now, the highest probabilities of at least 4 inches of snow=20
maximize from northern MO through the Chicago metro and into=20
central Lower MI, with >50% probs extending to the NW and SE by=20
about 100 miles. This includes cities such as Kansas City, Des=20
Moines, Chicago, Milwaukee, and Detroit, just to name a few. Within
this region, probabilities of at least 8 inches are moderate=20

40%) from northern MO to northern IL and across central Lower=20

Michigan.

Like areas farther upstream (southern Plains), a mix or sleet and=20
freezing rain is likely closer to the track of the surface low due=20
to the overrunning of the cold surface with warmer air aloft over=20
portions of central IN into northwestern OH. There, WPC=20
probabilities of at least 0.10" icing are low (10-40%).

The positive-tilt to the pattern will help move the system along,=20
with precipitation ending Thursday morning over Michigan, though NW
flow on the backside will stir up some lake effect snow for U.P.=20
and L.P. of MI. Amounts should be light at the end of this forecast
period (12Z Thu - 00Z Fri).


...Pacific Coast...
Days 2-3...

A large trough will amplify across the Intermountain West,=20
upstream of which shortwaves will begin to dig along the Pacific=20
coast as vorticity impulses shed east from an amplifying closed low
over the Pacific. While this low won't really become organized=20
until late D3, energy pivoting onshore beginning D2 will spread an=20
axis of moisture into central and southern CA, with snow in the=20
terrain above generally 3000-4000 ft. This impulse is weak and will
be directed almost due SW by the downstream trough, but WPC=20
probabilities are moderate (30-50%) for more than 6 inches across=20
primarily the southern Sierra D2.

After this first impulse, the closed low offshore begins to deepen
and pivot eastward. Height anomalies drop steadily offshore,=20
reaching as low as 1st percentile within the CFSR climatology by=20
00Z Friday near the CA/OR border, and the accompanying and=20
impressive downstream divergence will begin to displace the trough=20
with a brief period of shortwave ridging. Increasing moisture=20
advection onshore, driven by confluent mid-level flow south of this
closed low topped by a collocated strengthening jet streak will=20
surge IVT as high as 500 kg/m/s into the coast late Thursday. This=20
will manifest as expanding and intensifying precipitation, with the accompanying warm front/WAA lifting snow levels rapidly to as much
as 6000 ft in the Sierra. However, farther north into the=20
Shasta/Trinity region and into Oregon, pronounced cold air will be=20
slow to retreat, leading to some lowland snow potential as well as=20 overrunning/freezing rain. There continues to be a lot of=20
uncertainty in timing and placement, but there is high confidence=20
that this event will eventually result in heavy wintry=20
precipitation across the West. Current WPC probabilities are high=20

90%) for 12+ inches across much of the Sierra, generally above=20

4000 ft, and above 70% (above 3000 ft) in the=20
Shasta/Trinity/Klamath region. This could be quite impactful to=20
many area passes.


...Northeast...
Days 1 & 3...

On Tuesday, a strong cold front will race from the Great Lakes=20
through New England, bringing with it an increased risk for=20
convective snow showers and snow squalls. The high-res CAMs have=20
become more aggressive with their depiction of simulated=20
reflectivity along this front Tuesday aftn, suggesting a greater=20
threat for snow squalls. The greatest risk appears to be from=20
Upstate NY across northern New England which is where the best=20
overlap of 0-2km fgen and RH overlap, and although instability is=20
modest, the SnSq parameter does reach +2 across this region. This=20
may end up more as convective snow showers than true squalls, but=20
briefly intense snow rates and restricted visibility could cause=20
dangerous travel Tuesday afternoon/evening.

Then during D3 /00Z Thursday to 00Z Friday/ more significant=20
precipitation will overspread the region from SW to NE. This=20
precipitation will be associated with a robust low pressure lifting
across the Ohio Valley, driven by a modest shortwave on the=20
downstream edge of a deepening trough over the middle of the CONUS,
overlapped with the RRQ of a 150 kt poleward arcing jet streak=20
moving across the eastern Great Lakes. Downstream of this system,=20
moist advection will maximize in response to low-level WAA on S/SE=20
flow overrunning a retreating high pressure that will try to wedge=20
back to the west into New England. This will result in an expansion
of wintry precipitation, likely starting as snow everywhere before
gradually transitioning to sleet and freezing rain, especially=20
south of I-90, before winding down late D3 everywhere but ME/NH.

There is still considerable spread in the speed of this system=20
forecast by the deterministic global members, but at least moderate
snowfall accumulations are likely, especially in higher terrain,=20
as reflected by WPC probabilities that are above 50% for 4+ inches=20
from the Adirondacks across much of northern New England.=20
Additionally, light to moderate icing is possible as reflected by=20
WPC probabilities of 10-30% for 0.1" in the Catskills, Berkshires,=20
and Litchfield Hills.


Weiss/Fracasso/Snell



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!924NT_I-3Zl98BzXxxOT32R60yVgs-zliGxJOIussbPLs= zH6XP1sOUErxvXjklcPTVUan4DqII6uhbTzZFV8Y2CuX1E$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!924NT_I-3Zl98BzXxxOT32R60yVgs-zliGxJOIussbPLs= zH6XP1sOUErxvXjklcPTVUan4DqII6uhbTzZFV8kZDSEIc$=20

$$

=3D =3D =3D
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FOUS11 KWBC 170823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Mon Feb 17 2025

Valid 12Z Mon Feb 17 2025 - 12Z Thu Feb 20 2025


...Great Lakes...=20
Days 1-2...

Behind the exiting winter storm, cyclonic flow will remain over=20
the Great Lakes with 805mb temps < -20C. NW to WNW flow will favor=20
the typical MI belt regions but with an emphasis over the eastern=20
U.P. due to persistent light to moderate snow and especially=20
downwind of Lake Ontario. There, an intense single band may set up=20
today into Oswego and just north of Syracuse with some wavering N-S
into Tuesday. Two-day totals could exceed 18" (WPC probs > 50%)=20
with intense snowfall rates of 2-3"/hr. Strong pressure gradient in
place will keep winds elevated as well, creating blowing and=20
drifting of snow with especially hazardous whiteout conditions=20
within the band. Snow will gradually wind down into day 3.


...Pacific Northwest/Rockies/Northern High Plains...
Days 1-2...

An active Pacific jet will maintain unsettled weather into the=20
Northwestern U.S. for the next 24 hours or so over the Cascades=20
into the northern Rockies. Height falls will continue moving inland
this morning with modest snows following along out of the Cascades
and into the Bitterroots/western MT this evening. East of the=20
Continental Divide a very cold air mass will be in place thanks to=20
high pressure over Canada that pushes southward through the Plains,
setting up upslope flow into western MT. Snow totals will be light
to modest in the higher elevations where WPC probabilities for at=20
least 8 inches of snow are >70%. Over central MT, light snow due=20
to upslope/easterly flow is expected from Billings to Kalispell but
WPC probabilities for an additional 4 inches are low (<40%) in the
lower elevations. As the height falls move into the Plains, snow=20
will gradually diminish on Tuesday.=20

Day 3...

The next system will enter the Pacific Northwest starting Tuesday=20
Night with some periods of snow for the Cascades, including into=20
the passes. Moisture plume will aim into Oregon but then move=20
quickly inland, helping to spread snow into the Northern Rockies=20
throughout the day on Wednesday (especially into the Blue Mountains
and into the central Idaho ranges). WPC probabilities for >6" of=20
snowfall are high (>70%) in these areas.



...Central Plains/Mid-MS Valley/Mid-South...=20
Days 1-2...

The anomalous IVT responsible for periods of heavy snow in the=20
Rockies will accompany a period of 700mb WAA over the Central=20
Plains. The combination of 700mb FGEN and an accelerating 250mb jet
aloft will support a stripe of light/moderate snow from the Black=20
Hills southeastward through NE and into the Lower Missouri River=20
Valley today, weakening later today. Then tonight, the stronger=20
500mb shortwave trough tracking across the Central Rockies will=20
gradually deepen while upper-level diffluence increases at the nose
of a 250mb jet streak rounding the base of the Central Rockies=20
trough, setting up another area of snow from NW to SE. By early=20
Tuesday morning, KS will be within the entrance region of the upper
jet which will help promote an area of snow across central KS=20
where lower-level FGEN is maximized. Temperatures will be cold=20
behind an Arctic front, which should allow for SLRs ~15:1=20
especially in healthier bands. This area of snow will move=20
southeastward and increase in intensity into southeastern KS and=20
southern MO late Tue afternoon/evening where the 00Z CAM guidance=20
shows the potential for 1-1.5"/hr rates (per WPC snowband tool). By
early Wednesday the snow may diminish in intensity into KY as the=20
upper jet reorients itself and shifts focus to the Gulf coast,=20
setting up the coastal part of this event farther east. WPC=20
probabilities of at least 4 inches of snow are high (>70%) from=20
central KS eastward into MO and extreme southern IL. Within this=20
region, WPC probabilities for at least 8 inches of snow are=20
moderate (40-70%), especially over southern MO.

To the south of this swath of snow, cold surface temperatures=20
beneath >0C air aloft will promote an area of sleet and freezing=20
rain over central OK eastward into AR. A few hundredths of an inch=20
of icing is possible, especially into the Ouachita Mountains.


...Central/Southern Appalachians/Mid-Atlantic...=20
Day 3...

The next phase of the system moving out of the Mid-MS Valley has=20
been in quite a bit of flux. Question revolves around the timing=20
and amount of interaction between the shortwave responsible for the
snow across KY/northern TN and the lead height falls ahead of the=20
upper low over the western Great Lakes/Corn Belt. A surface wave=20
should develop near the Gulf coast by early Wed and track eastward=20
then east-northeastward just off the Southeast coast to become the=20
new focus for QPF. Models have been wavering quite a bit on the=20
amount of development and how close to the coast this may be,=20
influencing how much QPF to surge into the southern Mid-Atlantic.=20
Overall trend continues to be a flatter and drier system and have=20
trended that way tonight.=20

Nevertheless, there is confidence in the wave development and at=20
least light to moderate QPF that will spread into the Southeast and
southern Mid-Atlantic from the system. The result will be a swath=20
of snow over southern and southeastern VA and northern NC with an=20
area of sleet and potentially significant freezing rain to the=20
south over eastern NC where QPF will be plentiful. WPC=20
probabilities for at least 4 inches of snow are >50% across=20 southern/southeastern VA. Over NC, where the cold air in place=20
behind the departing system Sunday will be overrun with >0C air=20
aloft, the icing potential is significant. WPC probabilities for at
least 0.25" ice are at least 30% but may rise in future updates.=20


Fracasso



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!88JkGmUfN_py9gi_fPi9tnkICvm19DpncrXV_FjCLbGw8= W7F9D-CBFI5crUXN7rvJ_zPqTvsr4pU5RMZExfkBoS8QSo$=20

$$

=3D =3D =3D
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FOUS11 KWBC 110852
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
352 AM EST Tue Feb 11 2025

Valid 12Z Tue Feb 11 2025 - 12Z Fri Feb 14 2025


...Ohio Valley to the Mid-Atlantic...=20
Days 1-2...

Active pattern continues with two significant winter weather=20
events progged to impact the area with different hazards through
Wednesday night.

The first is already taking shape across the Mid-Mississippi and
Ohio valleys this morning as precipitation begins to expand from
the Ozarks to the southern Appalachians, with snow and a wintry mix
expected to stretch from near southern IL to southwest VA by the
start of D1 (12z/Tues). This precipitation shield will be the=20
result of an overlap of forcing and moisture expanding into the=20
region from the west and south. A shortwave trough and accompanying
vorticity maxima is racing eastward across the Southern Plains this
morning while also weakening in response to confluent/flat flow=20
across the eastern CONUS. Despite the modest amplitude of this=20
feature, ascent will intensify through modest PVA and mid-level=20
divergence overlapped with the right entrance region to a jet=20
streak amplifying to the northeast. A weak surface wave may develop
and skirt almost due east ejecting off the Mid-Atlantic early
Wednesday, but in general precipitation will be driven by the=20
overlap of the synoptic ascent and increasingly impressive moist=20
isentropic upglide/WAA emerging from the Gulf.

The moisture surging northward will be significant as reflected by
mixing ratios within the robust 290-295K isentropic ascent=20
reaching as high as 6-8 g/kg, drawing PWs as high as the 90th=20
climatological percentile as far north as southern VA. This
moisture flowing northward overrunning the cold airmass in place
from the Ohio Valley to Mid-Atlantic will lead to an expanding=20
swath of precipitation, with rounds of heavier rates likely=20
embedded near where mid-level fgen is strongest. There remains some
uncertainty with respect to the northern edge of the heaviest QPF,
mainly due to dry air intrusion and if the strengthening WAA can
overcome it. This will lead to a sharp northern gradient along the
Mason-Dixon Line and into central NJ. Marginal surface temperatures
at onset during the day will also limit snowfall accumulation. However,
there is high confidence that a stripe of heavier snowfall rates
overcoming these marginal surface temperatures will spread east=20
from Kentucky through Delaware. Snowfall rates of 1+"/hr are likely
at times, especially within the west-to- east oriented fgen band=20
progged to start in eastern KY this morning and central VA by the
afternoon before weakening and gradually lifting northward into
southern MD and the Delmarva Peninsula. This is in conjunction=20
with where 850-700mb fgen maximizes ascent and occurs in=20
conjunction with CSS (EPV* < 0.25) to support CSI. Where this band=20
develops, locally higher amounts of snow are possible, but in=20
general WPC probabilities spanning D1 and early D2 are high (>70%)=20
for more than 4" from eastern KY though the Central Appalachians=20
eastward to southern MD just south of Washington, D.C. Locally=20
higher totals are possible across the central Apps of WV and VA,=20
where WPC probabilities for at least 8" mostly low (10-30%) outside
of the highest elevations.=20

Farther to the south, a transition zone is still expected where a=20
mixture of snow, sleet, and freezing rain will occur due to an
800-850mb warm nose aloft and a textbook winter CAD signature east
of the Apps in the surface pressure pattern that is forecast to=20
linger through Wednesday. This area of mixed ptype is most likely=20
from KY and into the Central Appalachians, especially along the=20
Blue Ridge of NC/VA. While some sleet is possible, the predominant=20
mixed p-type is likely to be freezing rain within this axis, and=20
will almost certainly be significant (to locally damaging) in the=20
vicinity of the Blue Ridge.

This first event winds down late Wednesday morning through the=20
afternoon /D2/, but just as the column begins to dry aloft, renewed
WAA ahead of the next system approaches within this progressive=20
pattern. While the DGZ dries out across the Mid-=20
Atlantic/Appalachians, the low levels re-saturate, and it is=20
possible in some areas there is never a break in wintry=20
precipitation due to very light snow/snow grains/freezing drizzle=20
Wednesday. Eventually the column re-saturates though as a more=20
intense low pressure developing over the Southern Plains lifts=20
northeast into the Ohio Valley with another round of mixed=20
precipitation spreading into the region.

This second wave will be stronger, but also farther inland, so=20
many areas will begin with snow or freezing rain and eventually=20
transition to all rain. The heaviest precipitation will likely=20
begin right around Wednesday evening in the Central Appalachians=20
and then expand northeast into the Mid-Atlantic. High pressure=20
wedging into the region will again force impressive isentropic=20
overrunning, and locations from northern VA through PA will likely=20
begin as a burst of moderate snowfall before quickly transitioning=20
to sleet, freezing rain, and eventually all rain before waning=20
Thursday evening. The heaviest snowfall is likely in the Poconos
and central PA terrain where WPC probabilities for 2+ inches are=20
as high as 50-70%, with icing exceeding 0.1" likely (>70%) in the=20
Laurel Highlands and parts of the Poconos.

WPC event total probabilities (12z/Tues to 12z Thurs) for more=20
than 0.25" are above 70% in the vicinity of the Blue Ridge where=20
locally more than 0.5" is also expected for some areas (50%=20
chance). There also exists some non-zero (5-15%) probabilities for
at least 1" of ice in terrain of far northwest NC and adjacent VA.
This will cause severe impacts including power outages, scattered=20
tree damage, and dangerous travel. Surrounding this, WPC=20
probabilities for more than 0.1" of 10-30% encompass a much larger=20
area including into parts of south- central VA and up the=20
Appalachians to near the MD Panhandle and Laurel Highlands.


...Central Rockies/Plains/Midwest/Great Lakes...=20
Days 1-3...

Troughing over the northern Great Basin this evening will dip into
the central Rockies tonight, with broad WSW flow across CO. This=20
will favor an expansion of snowfall over the Medicine Bow mountains
and into the San Juans/Sangre de Cristos where upslope enhancement
will wring out several inches of snow area-wide. For the D1=20
period, WPC probabilities for at least 6 inches of snow are >50%=20
above 10,000ft or so.=20

By late tonight into early Wednesday, troughing will pass the=20
spine of the Rockies as low- level moisture increases over the=20
foothills to the Plains via SE to E flow. This will combine with NE
flow at the surface to increase snow into the Front Range, though=20
snow should generally be light overall. WPC probabilities for at=20
least 4 inches are near 20-30% over parts of the I-25 corridor.=20

The more intense snowfall will manifest farther east over Kansas
and southern Nebraska starting late tonight into Wednesday. There,
the potential exists for moderate to heavy snow across much of=20
Kansas as the upper jet extends from TX northeastward to the=20
Midwest. Combination of WAA, tightening thermal gradient=20
(increasing FGEN), and favorable/deep DGZ/isothermal layer will=20
promote locally heavy snow with >1"/hr rates (per WPC snowband=20
tool). A large high pressure to the north will supply NE winds to=20
the region but the gradient is not expected to be strong enough to=20
produce much blowing snow even as low pressure deepens over the=20
ArkLaTex. SLRs may eclipse 20:1 in the most favorable bands but=20
otherwise hover close to 15:1 along the I-70 corridor from GLD to=20
MCI. Further southeast across parts of central Oklahoma through
southeast Kansas and southern/central Missouri, overrunning will=20
favor sleet and freezing rain. WPC probabilities for at least 0.1"
ice are low- moderate in this region (10-50%) and highest over
Missouri. For snowfall, PVA and FGEN will force much of the=20
precipitation in advance of the trough with the axis of heavier=20
snowfall along I-70 toward/into Kansas City, then extending=20
northeastward. WPC probabilities for at least 4 inches of snow are=20
high (>80%) over most of central/northern KS into southern NE with
some probs (30-50%) for at least 8 inches.

By Wednesday night, the system begins to further organize and pick
up forward speed as a relatively weak surface low (>1000mb) lifts=20
through the Ohio and Tennessee valleys. The lack of rapid
deepening of the low pressure system due to the quickly lifting
longwave trough will prevent impacts associated with blowing and
drifting snow. Snow is expected to expand from southern IA and=20 northern/central MO through much of IL, southern WI, northern IN,=20
and the L.P. of Michigan. A narrow corridor of mixed ptype is also=20
forecast in a southwest to northeast band from southern MO through=20
central IN and northwestern OH. This narrow corridor of mixed ptype
could remain relatively stationary for a period of time across
Indiana and northwest Ohio for measurable freezing rain and sleet.
The combination of strong PVA and lower level FGEN into a deep DGZ
should provide for an axis of heavier snow, but where that=20
materializes is still bit fuzzy (including any lake enhancement=20
off Lake Michigan on NE winds) as some uncertainty in the 700 mb
fgen field and high SLR environment could prompt multiple areas of
enhancement.

Right now, the highest probabilities of at least 6 inches of snow=20
maximize from northern MO through the Chicago metro and into=20
central Lower MI, with >60% probs extending to the NW and SE by=20
about 150 miles. This includes cities such as Kansas City, Chicago
and Milwaukee just to name a few. Within this region,=20
probabilities of at least 8 inches are moderate (>40%) from=20
northern MO to northern IL and across central Lower Michigan.

Like areas farther upstream (southern Plains), a mix or sleet and=20
freezing rain is likely closer to the track of the surface low due=20
to the overrunning of the cold surface with warmer air aloft over=20
portions of central IN into northwestern OH. There, WPC=20
probabilities of at least 0.10" icing have increased this forecast
cycle and are moderate (40-60%).

The positive-tilt to the pattern will help move the system along,=20
with precipitation ending Thursday morning over Michigan, though NW
flow on the backside will stir up some lake effect snow for U.P.=20
and L.P. of MI. Amounts should be light at the end of this forecast
period (12Z Thu - 12Z Fri).


...Sierra Nevada into much of the West...=20
Days 1-3...

As a large trough amplifies across the Intermountain West,=20
upstream shortwaves will begin to dig along the Pacific coast as=20
vorticity impulses shed east from an amplifying closed low over the
Pacific. While this low won't really become organized until late=20
D3, energy pivoting onshore beginning late D1 will spread an axis=20
of moisture into central and southern CA, with snow in the terrain=20
above generally 3000-4000 ft. This impulse is weak and will be=20
directed almost due SW by the downstream trough, but WPC=20
probabilities are moderate (30-50%) for more than 6 inches across=20
primarily the southern Sierra D1.5.

After this first impulse, the closed low offshore begins to deepen
and pivot eastward. Height anomalies drop steadily offshore,=20
reaching as low as 1st percentile within the CFSR climatology by=20
00Z Friday near the CA/OR border, and the accompanying and=20
impressive downstream divergence will begin to displace the trough=20
with a brief period of shortwave ridging. Increasing moisture=20
advection onshore, driven by confluent mid-level flow south of this
closed low topped by a collocated strengthening jet streak will=20
surge IVT as high as 500 kg/m/s into the coast late Thursday. This=20
will manifest as expanding and intensifying precipitation, with the accompanying warm front/WAA lifting snow levels rapidly to as much
as 6000 ft in the Sierra. However, farther north into the=20
Shasta/Trinity region and into Oregon, pronounced cold air will be=20
slow to retreat, leading to some lowland snow potential as well as=20 overrunning/freezing rain. Moisture will then quickly spread
throughout the Intermountain West through the end of the period
(12z/Fri) along with the progressing, but weakening upper trough.
There continues to be some uncertainty in timing and placement,=20
but there is high confidence that this event will eventually result
in heavy wintry precipitation across the West. Current WPC=20
probabilities are high (>90%) for 18+ inches across much of the=20
Sierra, generally above 4000 ft, and above 70% for 12+ inches (above
3000 ft) in the Shasta/Trinity/Klamath region. This could be quite
impactful to many area passes. Further east into the Intermountain
West and central Rockies, high probabilities (>70%) for at least 8+
inches of snow exists across the Wasatch into the Tushar Mts of
Utah, as well as the San Juan Mts of Colorado.


...Northeast...
Days 1 & 3...

Today, a strong cold front will race from the Great Lakes through=20
New England, bringing with it an increased risk for convective snow
showers and snow squalls. The high-res CAMs remain aggressive with
their depiction of simulated reflectivity along this front Tuesday
aftn, suggesting a greater threat for snow squalls. The greatest=20
risk appears to be from northern Upstate NY across northern New=20
England which is where the best overlap of 0-2km fgen and RH=20
overlap, and although instability is modest, the SnSq parameter=20
does reach +2 across this region on the 00z GFS. This may end up=20
more as convective snow showers than true squalls, but briefly=20
intense snow rates and restricted visibility could cause dangerous=20
travel this afternoon/evening.

Then during the end of D2 and into D3 (centered around 00Z Thursday
to 00z Friday) more widespread significant precipitation will=20
overspread the region from SW to NE. This precipitation will be=20
associated with a robust low pressure lifting across the Ohio=20
Valley, driven by a modest shortwave on the downstream edge of a=20
deepening trough over the middle of the CONUS, overlapped with the=20
RRQ of a 150 kt poleward arcing jet streak moving across the=20
eastern Great Lakes. Downstream of this system, moist advection=20
will maximize in response to low- level WAA on S/SE flow=20
overrunning a retreating high pressure that will try to wedge back=20
to the west into New England. This will result in an expansion of=20
wintry precipitation, likely starting as snow everywhere before=20
gradually transitioning to sleet and freezing rain, especially=20
south of I-90, before winding down Thursday night.

There is growing confidence with the speed of the system, with at=20
least moderate snowfall accumulations likely, especially in higher
terrain and northern Maine, as reflected by WPC probabilities that
are above 50% for 4+ inches from the Adirondacks across much of=20
northern New England, with >80% probs in northern Maine.=20
Additionally, light to moderate icing is possible as reflected by=20
WPC probabilities of 10-30% for 0.1" in the Catskills, Berkshires,=20
and Litchfield Hills.


Weiss/Fracasso/Snell




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!733NuN3T5tGROpnLE55wv86D3Xg26LKkO0-1wTO9LWL1n= pUm0euIqQ1AgJb2Y3CniJCu7-VPpZzRDSSb5h8hbTxccaQ$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!733NuN3T5tGROpnLE55wv86D3Xg26LKkO0-1wTO9LWL1n= pUm0euIqQ1AgJb2Y3CniJCu7-VPpZzRDSSb5h8hdACHgfk$=20

$$

=3D =3D =3D
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FOUS11 KWBC 112121
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
421 PM EST Tue Feb 11 2025

Valid 00Z Wed Feb 12 2025 - 00Z Sat Feb 15 2025


...Mid-Atlantic...=20
Day 1...

...Winter Storm Ongoing Across the Mid-Atlantic with Impacts from=20 Significant Icing and Heavy Snow. Key Messages linked below...

A winter storm ongoing across the Virginias has already produced=20
multiple inches of snow from southern West Virginia through central=20 Virginia, with icing reports along the Blue Ridge in North Carolina.=20
Local storm reports show the highest snowfall amounts as high as=20
12 inches in the Allegheny Highlands of WV/VA. Meanwhile radar=20
shows the heaviest snowfall rates in a swath across north-central=20
Virginia into southern Maryland where snowfall rates over an inch=20
per hour are also being reported.

This storm is being caused by intensifying warm advection moving=20
over a stubbornly cold air mass caused by a 1030 mb area of high=20
pressure centered off of Nantucket. Thus, the predominant flow is=20
easterly. This flow off the Atlantic will become increasingly warm=20
with time as the flow turns more southeasterly. Any warming is=20
being countered by the aforementioned heavy snow rates, leading to=20
dynamic cooling by the sheer volume of the heavy falling snow.=20
Meanwhile in the mid-levels (850 mb) the flow will be south to=20
southwesterly throughout the event, though increasing in intensity=20
through this evening. In the upper levels, all of the lift will be=20
driven by the right entrance region (RER) of a 150+ kt jet over New
England. It's important to note that other than the jet, there=20
will be very little if any additional upper level support from any=20 shortwaves. Therefore, most of the support will be from warm=20
advection of a warm air mass over the colder air mass that remains=20 persistent near the surface.

Weak 700 mb waves will track along the plume of moisture which=20
extends from east Texas to the Delmarva. These will lead to=20
localized increases in intensity of the precipitation through=20
tonight. The rain-snow line is unlikely to move much from its=20
current position across much of southern Virginia through tonight.=20
A weak surface low/trough will from late tonight (around 06Z) off=20
the Virginia coast which will pull the precipitation plume east=20
into the Atlantic and largely end the wintry side of the event from
west to east. There is some disagreement in the high resolution=20
models as to when this will happen however, as a secondary weaker=20
wave may keep light frozen precipitation ongoing over northern VA=20
and the Delmarva as late as sunrise Wednesday morning. Ultimately=20
the snow event will end once drier air and a lack of mid-level=20
disturbances can overcome an otherwise saturated air mass that=20
stands ready to produce additional light precipitation at a=20
moment's notice.

While dynamically this snowfall event will be the weaker of the two=20
storms (the other described below over the central Plains to the=20
Great Lakes), it may be the longer-duration of the two for portions=20
of the Virginias, so the highest snowfall accumulations between the=20
two storms could very well be similar.

To the south along the rain-snow line, there is expected to be a=20 long-duration ice event due to freezing rain for portions of the=20 Appalachians from central West Virginia through the Blue Ridge and=20 Shenandoah Valley from Roanoke, VA south into far northwestern North=20 Carolina. As mentioned above, strong warm advection in the mid-
levels will override colder air near the surface, unlike further=20
north where the warm air will fail to warm temperatures above=20
freezing in the midlevels, further south the warmer air will succeed=20
at both eroding the cold air enough to warm temperatures in the mid-
levels above freezing, the cold air will remain stout at the=20
surface, even as a shallow layer. This will set up the potential for=20 prolonged icing. Most of the precipitation will occur with this=20
first storm that is ongoing now. Some areas around Roanoke have=20
started the storm as snow but will transition to freezing rain as=20
the warm air aloft in this area has some success at impinging=20
northward tonight. Icing for many may exceed a quarter inch, and=20
could approach a half inch through Wednesday morning in the areas=20
where both the surface cold air and precipitation persist the=20
longest.

Late tonight into Wednesday, most of the central Mid-Atlantic will
be dry or light drizzle with pockets of freezing rain lingering=20=20
over the VA Piedmont and on ridges which would further add to ice
impacts.

WPC probabilities are moderate (50-60%) for 1/4 inch of ice along I-
81 south of Roanoke south to extreme northwestern North Carolina,=20
though amounts drop to very low (5-10%) for 1/2 inch of ice. On the=20
snow side, probabilities are moderate to high (60-70%) for at least=20
6 inches of snow north and west of Roanoke, some of those have=20
already been realized). Farther east, those probabilities are low=20
to moderate (30-40%) from DC south along I-95 through=20
Fredericksburg, VA.


...CO Rockies/Central Plains/Midwest/Great Lakes...=20
Days 1/2...

...Winter Storm expected starting over Kansas/Nebraska spreads=20
northeast across Lower Michigan through Wednesday Night...

Troughing over the northern Great Basin will dip into the central=20
Rockies tonight with broad WSW flow across CO. This will favor an=20
expansion of snowfall over the Medicine Bow mountains and into the=20
San Juans/Sangre de Cristos where upslope enhancement will wring=20
out several inches of snow area-wide. Snow probs after 00Z for >6"
are 40-60% above about 8000ft in portions of the Sawatch and San
Juan Mtns.

Downstream, a winter storm is developing over the Central Plains=20
while the one over the Mid-Atlantic one persists into tonight. For=20
forcing, there will be some notable differences between the two=20
storms. While there will certainly be some warm advection bringing=20
Gulf moisture north into the central Plains and Midwest, this storm
will be much more dynamic in the upper levels. A broad longwave=20
trough over the northern Plains will begin to shift eastward as a=20
potent shortwave trough rounds the southern periphery of the=20
trough. This will enhance the downstream jet, which will intensify=20
the forcing needed for surface cyclogenesis from the southern=20
Plains and eventually into the Ohio Valley. Thus, the expected=20
swath of snowfall associated with this low will be associated with=20
a well- developed surface low in much more of a "classic" form.

With the intensifying and fast-moving low providing the primary=20
forcing for the snowfall, expect heavy snow to develop across=20
central Kansas tonight, and track northeastward across far=20
northwestern Missouri, central and eastern Iowa, far northern=20
Illinois, southern Wisconsin, and across much of the Lower=20
Peninsula of Michigan through Wednesday night. The low will be=20
plenty strong enough to produce bands of heavy snow embedded within
the comma- head region as it picks up Gulf moisture to its=20
south...but due to the fast moving nature of the low, the duration=20
of any heavy snow, especially outside of any banding will be=20
shorter than the current Mid-Atlantic storm.

On Wednesday, as the storm moves into the left exit region of a=20 southwest-to-northeast oriented jet, the snow will spread into the=20
Midwest and upper Lakes. With lake-enhancement on the northeasterly=20
winds, there may be locally heavier snow and higher accumulations=20
southwest of Lake Michigan, which may include the Chicago and=20
Milwaukee metros. Of course, this will be highly dependent on where=20
any embedded bands associated with the storm can line up with the=20
lake, resulting in the localized enhancement. Blowing and drifting=20
of snow in the strong winds is likely right along the lake shore.=20
Additional enhancements are possible along the Lake Huron shoreline=20
into Wednesday night for the same reason...a rather unusual=20
direction for Lake Huron enhanced snowfall.

On the southern side of the comma-head region of the low, enough=20
warm air is expected to move in around the center of the low to=20
result in an area of mixing/freezing rain just south of the swath of=20
snow from central Oklahoma tonight northeast across much of southern=20 Missouri, including the St. Louis area, then extending northeast=20
across central Indiana, including the Indianapolis area, and into=20
far northwestern Ohio, including the Toledo area. Each of these=20
areas, and of course those in between, have the potential to see=20
some light to moderate icing, up to 1/4 inch. Once again the timing=20
of any icing should be shorter than areas further east, which should=20
limit any icing accumulations and thus, the magnitude of any impacts.

WPC probabilities for ice are moderate (40-60%) for 1/10 inch of=20 accumulation from northeast of Indianapolis northeast through=20
Toledo, OH. Probabilities are low (5-30%) for 1/10 inch of ice from=20
south of St. Louis northeast through Indianapolis. For snowfall,=20 probabilities for 6 inches or more are moderate (40-60%) for much of=20 northern Kansas through south-central Iowa, lower (20-40%) through
eastern Iowa and northwestern IL, then increase back to the=20
moderate category (40-70%) along the lakeshore in Wisconsin due to=20 lake-enhancement from Milwaukee south to northern Chicago, as well
as for much of eastern Michigan north of Detroit.


...Sierra Nevada and much of the West...=20
Days 1-3...

Day 1...
An expansive, positively-tilted trough lingers over the west=20
into Wednesday with northwest flow persisting over CA. A shortwave
impulse rides along the central CA coast tonight into Wednesday
producing areas of light to locally moderate precip with snow
levels around 3000ft in the southern Sierra Nevada and around
4000ft in the SoCal transverse and peninsular ranges. Day 1 Snow
probs for >4" are 30-50% in the southern Sierra Nevada and the
highest SoCal ranges such as near Big Bear.=20

Days 2-3...
A stronger low shifts toward the OR/CA border Wednesday night,
opening into a trough as it drifts east over the Great Basin
through Friday. A strengthening and increasingly northerly jet
shifts toward the West Coast Thursday night. An atmospheric river
with IVT around 500 kg/m/s shifts over the CA coast Wednesday night
through Thursday. A wave of moderate to topographically enhanced
heavy precip shifts east with the accompanying warm front Wednesday
night through Thursday. Snow levels over the Sierra Nevada are
initially 3000ft Wednesday evening, but quickly rise to 6000ft by=20
Thursday morning. Both Days 2 and 3 snow probs for >18" are high
along the length of the Sierra Nevada with 4-6ft forecast for the
High Sierra through Friday.=20
Farther north into the Shasta/Trinity region and Oregon,=20
pronounced cold air will be slow to retreat, with snow levels=20
generally rising only from 2000ft to 4000ft through Thursday with=20
lower precip rates than in the core of the AR over CA. Day 2.5
snow probs for >12" are 50-80% for the Shasta/Siskiyou/Trinity=20
Mtns and Day 3 snow probs for >8" are 40-70% for the OR Cascades.

The lingering cold air brings light lowland snow potential for=20
much of the PacNW with an appreciable threat for freezing rain=20
mainly Thursday over northwest OR. Day 2.5 ice probs for >0.1"=20
are 30-60% for mainly the Coast Ranges west of the Willamette=20
Valley.=20

Moisture quickly spreads east throughout the Intermountain West=20
Thursday through Friday ahead of the slow moving trough axis. Day 3
snow probs for >8" are above 70% for the Wasatch and Tushar Mtns in
Utah as well as for western slopes of the CO Rockies and around=20
50% for the western Sawtooths and Tetons into southeast ID.=20


...Northeast...
Day 2...

The system coming from Michigan Thursday morning will bring
widespread precipitation from SW to NE over the Northeast.=20
Downstream of this system, moist advection will maximize in=20
response to low-level WAA on S/SE flow overrunning a retreating=20
high pressure that will try to wedge back to the west into New=20
England. This will result in an expansion of wintry precipitation
Wednesday night through Thursday with a wintry mix expected across
the Northeast with the far northern NY border east of Lake Ontario
and northern Maine getting the most snow. Day 2 snow probs for >4"
are limited to the Tug Hill, Adirondacks, Greens, Whites, and
interior Maine with 40% for >8" over the Thousand Islands area and
60% over northern Maine. Day 2 ice probs for > 0.1" are 20-30% in
the Poconos, Catskills, and Berkshires into the Litchfield Hills.


Jackson/Wegman


...Winter Storm Key Messages are in effect...

Central Plains through Midwest Winter Storm tonight into Thursday: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-rnDq3Ng21EUtfmuNYpmKCeiGDMyfJH2dvW331ircDYUN= OB2Fr4KTycEWLTWwbhEP688O8_YJVs_3J-sipQIUbCqqQQ$=20

Mid-Atlantic Winter Storm continuing tonight for snow/Wednesday
night for ice: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-rnDq3Ng21EUtfmuNYpmKCeiGDMyfJH2dvW331ircDYUN= OB2Fr4KTycEWLTWwbhEP688O8_YJVs_3J-sipQIt47tiDE$=20

Key messages are also in effect for the Atmospheric River into
California Wednesday night into Friday and can be found on Weather
Prediction Center social media.=20


$$

=3D =3D =3D
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FOUS11 KWBC 120808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Wed Feb 12 2025

Valid 12Z Wed Feb 12 2025 - 12Z Sat Feb 15 2025


...Mid-Atlantic...=20
Day 1...

...Winter Storm Ongoing Across the Mid-Atlantic with Impacts from=20 Significant Icing the Primary Concern Today. Key Messages linked=20
below...

Heavy precipitation is expected to wind down across the Mid-
Atlantic early D1 (12z Wednesday) as a weak surface low exits
eastward into the Atlantic along with the direct IVT. However,
lingering light snow and freezing drizzle is possible during the
day as the lower levels fail to dry out entirely due to persistent
mid-upper level flow riding overtop the surface CAD signature.
Then, as the central U.S. storm strengthens from a neutral turning
negatively tilted upper trough, IVT restrengthens and even becomes
extreme (maxing out the NAEFS climatological percentiles for 06z
into western NC) by tonight. This allows for an increase in both=20
WAA and precipitation this afternoon and evening across the=20
central Appalachians and Mid-Atlantic. Given the very strong WAA,=20 precipitation type will mostly fall as freezing rain and a bit of=20
sleet outside of some brief snow possible in northern MD/PA.=20
Freezing rain will also confine to areas right along the Blue Ridge
and Central Appalachians quickly this evening. For western NC and=20
SW VA this will only add to the already reported significant ice=20
accretion from the prior day. WPC probabilities for an additional=20
0.25"+ of freezing rain are moderate (40-60%) across far western=20
NC, SW VA along the Blue Ridge, and along the hilly/mountainous=20
terrain following the VA-WV border. Additionally, low probabilities
(<10%) exist across far western MD and the Laurel Highlands of PA.


...Central Plains to Great Lakes...=20
Days 1-3...

...Winter Storm continues across the Central Plains and Midwest=20
before spreading into the Great Lakes today. Heavy lake-effect=20
snow is expected downwind of Lake Ontario beginning Thursday=20
night...

An upper shortwave ejecting out of the central Rockies this morning
will take on a negative tilt and provide ample broad lift within
strong southwesterly flow across the central U.S. directed at the
Great Lakes. Additionally, a southwest-northeast oriented jet is
expected to place the system into the left exit region, with a
precipitation shield beginning this morning between CO and IA=20
before making it's way into the Great Lakes this evening. With=20
lake- enhancement on the northeasterly winds, there may be locally=20
heavier snow and higher accumulations southwest of Lake Michigan,=20
which may include the Chicago and Milwaukee metros. Of course, this
will be highly dependent on where any embedded bands associated=20
with the storm can line up with the lake, resulting in the=20
localized enhancement. Blowing and drifting of snow in the strong=20
winds is likely right along the lake shore. Additional enhancements
are possible along the Lake Huron shoreline into Wednesday night=20
for the same reason...a rather unusual direction for Lake Huron=20
enhanced snowfall. Snow ratios will differ drastically depending on
location, with extremely favorable DGZ and moist columns along the northern/northwest side of the system (GID confirmed 29:1 ratios at
midnight CST), with less favorable conditions closer to the=20
surface low center. This may help enhance snowfall totals across
the northern half of the precipitation shield.

On the southern side of the comma-head region of the low, enough=20
warm air is expected to move in around the center of the low to=20
result in an area of mixing/freezing rain just south of the swath of=20
snow from central Oklahoma early this morning across much of=20
southern Missouri, including the St. Louis area, then extending=20
northeast across central Indiana, including the Indianapolis area,=20
and into far northwestern Ohio, including the Toledo area. Each of=20
these areas, and of course those in between, have the potential to=20
see some light to moderate icing, up to 1/4 inch. Once again the=20
timing of any icing should be shorter than areas further east,=20
which should limit any icing accumulations and thus, the magnitude=20
of any impacts.

WPC probabilities for ice are moderate (40-60%) for 1/10 inch of=20 accumulation from northeast of Indianapolis northeast through=20
Toledo, OH. Probabilities are low (5-30%) for 1/10 inch of ice from=20
south of St. Louis northeast through Indianapolis. For additional snowfall, probabilities for 6 inches or more are low (10-30%) for much of=20
northern Missouri through eastern Iowa and northern IL, then=20
increase back to the moderate category (40-60%) along the=20
lakeshore in Wisconsin due to lake- enhancement from Milwaukee=20
south to northern Chicago, as well as for much of eastern Michigan=20
north of Detroit (highest probs (>60%) in eastern Lower Michigan).

Following the passage of the surface low across the Lower Great
Lakes at the beginning of D2 (12z Thursday), strong high pressure
building into the Mid-Mississippi Valley will prompt strong west-
northwesterly flow over the cool, but mostly open Great Lakes
(around 26% ice cover). After a brief period of favorable
conditions for snow showers forming off lakes Superior and Michigan
early D2, focus turns to Lake Ontario Thursday through Friday
afternoon as -15 to -20C 850mb temperatures pass over the area. WPC probabilities for at least 8" are high (70-80%) from the southeast
lakeshore through southern Oswego county, NY. Snowfall totals
locally up to a foot are possible.


...Northeast...
Day 1-2...

The system coming from Michigan Thursday morning will bring
widespread precipitation from SW to NE over the Northeast.=20
Downstream of this system, moist advection will maximize in=20
response to low-level WAA on S/SE flow overrunning a retreating=20
high pressure that will try to wedge back to the west into New=20
England. This will result in an expansion of wintry precipitation
Wednesday night through Thursday with a wintry mix expected across
the Northeast with the far northern NY border east of Lake Ontario
and northern Maine getting the most snow. In fact, for northern
Maine a favorable setup for a lifting WAA band of heavy snowfall
appears likely on Thursday supporting snowfall rates up to 2" per
hour. Model cross sections depict strong 850-700mb fgen at the
bottom of a deep DGZ, supporting heavy QPF and efficient snow
ratios. Day 2 snow probs for >4" are limited to the Tug Hill,=20
Adirondacks, Greens, Whites, and interior Maine with 70% for >8" in=20
northern Maine. Day 1-2 ice probs for > 0.1" are 20-30% in the=20
Poconos, Catskills, and Berkshires into the Litchfield Hills.


...Sierra Nevada and much of the West...=20
Days 1-3...

An expansive, positively-tilted trough lingers over the west=20
into today with northwest flow persisting over CA. A shortwave=20
impulse rides along the central CA coast early this morning=20
producing areas of light to locally moderate precip with snow=20
levels around 3000ft in the southern Sierra Nevada and around=20
4000ft in the SoCal transverse and peninsular ranges. Then, a=20
stronger low shifts toward the OR/CA border tonight and into D2
especially, opening into a trough as it drifts east over the Great
Basin through D3. A strengthening and increasingly northerly jet=20
shifts toward the West Coast Thursday night. An atmospheric river=20
with IVT around 500 kg/m/s shifts over the CA coast Wednesday night
through Thursday. A wave of moderate to topographically enhanced=20
heavy precip shifts east with the accompanying warm front tonight=20
through Thursday. Snow levels over the Sierra Nevada are initially=20
3000ft Wednesday evening, but quickly rise to 6000ft by Thursday=20
morning. Day 2 snow probs for >18" are high along the length of=20
the Sierra Nevada with 4-6ft forecast for the High Sierra through=20
Friday. Farther north into the Shasta/Trinity region and Oregon,=20
pronounced cold air will be slow to retreat, with snow levels=20
generally rising only from 2000ft to 4000ft through Thursday with=20
lower precip rates than in the core of the AR over CA. Day 2.5 snow
probs for >12" are 50-80% for the Shasta/Siskiyou/Trinity Mtns and
Day 3 snow probs for >8" are 40-70% for the OR Cascades.

The lingering cold air brings light lowland snow potential for=20
much of the PacNW with an appreciable threat for freezing rain=20
mainly Thursday over northwest OR up along the Coastal Ranges. Day
2 ice probs for >0.1" are 40-67% for mainly the Coast Ranges west=20
of the Willamette Valley.=20

Moisture quickly spreads east throughout the Intermountain West=20
Thursday through Friday ahead of the slow moving trough axis. Day
2-3 snow probs for >8" are above 70% for the Wasatch and Tushar=20
Mtns in Utah, western slopes of the CO Rockies, as well as into the
Sawtooths of ID and western WY ranges.


...Upper Midwest and Great Lakes...
Day 3...

As the upper trough crosses the Intermountain West and Rockies on
Friday, it prompts a strengthening southwesterly oriented jet
streak across the Plains by late D3 and places the Upper Midwest in
the favorable left-exit region. Additionally, model guidance
suggests an inverted surface trough and potent axis of 700 mb WAA
may allow for additional lift beginning across the Upper Midwest
Friday before sliding eastward into Lower Michigan by Saturday=20
morning. Current WPC probabilities for at least 4 inches are=20
moderate (40-70%) across much of central/southern Wisconsin. There=20
remains some spread in the amplitude of the western trough and=20
influence from northern stream energy across Canada, so more=20
forecast refinements are likely in the coming days.


Snell



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!6JjBpX6gvHC_uwYBUq26lADdaXDk1mLzNiVsUPl3CVLgf= Y-CURvDjtFMKAmZ92DURN5bfbsu2yKWZB0fak8rkTwPUu0$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!6JjBpX6gvHC_uwYBUq26lADdaXDk1mLzNiVsUPl3CVLgf= Y-CURvDjtFMKAmZ92DURN5bfbsu2yKWZB0fak8r_znI-uw$=20

$$

=3D =3D =3D
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FOUS11 KWBC 122112
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
412 PM EST Wed Feb 12 2025

Valid 00Z Thu Feb 13 2025 - 00Z Sun Feb 16 2025


...Central Appalachians...=20
Day 1...

...Next winter storm will further enhance freezing rain concerns
over the central Appalachians into tonight. Key Messages linked=20
below...

A shortwave impulse is over AR/MO this afternoon which is on the
leading edge of a sprawling, positively-tilted trough axis over the
Rockies. This is bringing Gulf moisture up across the Southeast
into the Ohio Valley and up the Mid-Atlantic. Precip has once again
overspread southern VA, but given the strong warm nose, this is=20
rain over the coastal plains and well into the Piedmont. However,=20
afternoon temperatures are at or below freezing from the Blue Ridge
foothills and west over Virginia to the Allegheny Plateau in=20
central WV, then south along the crest of the Appalachians into NC
and north through the Laurels of PA. This cold will only slowly
erode tonight with continued freezing rain, adding to the existing
ice impacts. WPC Day 1 ice probabilities for >0.25" additional ice
after 00Z are around 10% for the Allegheny Highlands of VA with
40-60% probabilities for >0.1" from southwest VA north through the
Blue Ridge/Shenandoah Valley, Potomac Highlands, Laurels, and up
through the Allegheny National Forecast in northwest PA.


...Great Lakes and Northeast...=20
Days 1-2...

...Winter Storm continues over the Midwest and Great Lakes tonight,
spreading over Northeast Thursday. Prolonged heavy lake-effect=20
snow downwind of Lake Ontario Thursday night into Friday...

Shortwave trough over MO will lift over the Great Lakes tonight
before amplifying as it tracks over the Northeast Thursday. A sign
of this amplification is a re-strengthening of SWly jet over the
eastern Great Lakes tonight and over New England Thursday with a
return of 150kt flow by 12Z Thursday. Decent banding lingers from Des
Moines through Milwaukee to across MI north of Grand Rapids on the
north side of a dry slot in the developing wave. Ideal DGZ depth is
making for good snow rates in this band which will continue rest of
this evening west of Lake Michigan and into the overnight over the
L.P. of MI. This axis extrapolated ENE over the Northeast overnight
and Thursday tracks very near the northern NY border with heavy
snow generally over the Thousand Islands NY and across northern
Maine. Warm air advection makes for a wintry mix over much of the
rest of the Northeast/New England tonight/Thursday with snow=20
changing to some sleet and freezing rain.

Day 1 snow probs for >6" are 20-50% over eastern MI north of
Detroit, in the 30-50% range for the Adirondacks, Greens, Whites,
and northern Maine as well as long the northern NY border. Freezing
rain probs for >0.1" ice is 20-40% for the Poconos, Catskills,
Berkshires, southern Greens and Whites.=20

Following the passage of the surface low across the eastern Great=20
Lakes Thursday morning, 1035mb+ high pressure building into the=20
Mid- Mississippi Valley will prompt strong WNWly flow over open=20
Great Lakes (Erie is ice covered). After a brief period of=20
favorable conditions for snow showers forming off lakes Superior=20
and Michigan Thursday morning, focus turns to Lake Ontario=20
Thursday afternoon through Friday as -15 to -20C 850mb=20
temperatures cross. Day 2 WPC probabilities for >8" are 40-70%=20
from the southeast lakeshore through southern Oswego county, NY to
a line over the north side of Syracuse. Snowfall totals locally=20
over a foot are possible.


...Sierra Nevada, Pacific Northwest through the Rockies...=20
Days 1-3...

...Atmospheric River with heavy Sierra Nevada snow affects
California tonight into Friday. Key Messages are linked below...=20

Upper low centered out near 140W west of the OR/CA border is
directing an atmospheric river (AR) that reaches the northern CA
coast this evening and shifts south down the coast to southern CA
through Thursday night as the low opens into a slow moving trough.

The atmospheric river has IVT around 500 kg/m/s making for a wave=20
of moderate to topographically enhanced heavy precip tonight
through Thursday night over the Sierra Nevada. Snow levels over=20
the Sierra Nevada are initially 4000ft at onset this evening,=20
quickly rise to 7000ft by Thursday morning, then drop back to
6000ft under the trough axis Thursday night. Both Days 1 and 2 snow
probs for >18" are high along the length of the Sierra Nevada with=20
4-7ft forecast for the High Sierra through Friday.=20

Farther north into the Shasta/Trinity region and Oregon,=20
pronounced cold air will be slow to retreat, with snow levels=20
generally rising only from 2000ft to 4500ft through Thursday with=20
lower precip rates than in the core of the AR over CA. Day 1.5=20
snow probs for >12" are 50-80% for the higher Shasta/Siskiyou/=20
Trinity Mtns and Day 2 snow probs for >8" are 50-80% for the OR=20
Cascades.

The lingering cold air brings light lowland snow and ice potential
for southern WA through western OR. An appreciable freezing rain
threat is over northwestern OR Thursday/Thursday night mainly=20
along the Coastal Ranges. Day 1.5 ice probs for >0.1" are 40-80%=20
for mainly the Coast Ranges west of the Willamette Valley.=20

Moisture quickly spreads east throughout the Intermountain West=20
Thursday through Friday ahead of the slow moving trough axis. Day
2 snow probs for >8" are above 80% for the Tetons through the Wasatch
and Tushar Mtns (UT) and across the western slopes of the CO=20
Rockies with around 50% probs still for the Sawtooths of ID, and
Kaibab Plateau in AZ and northern NM ranges. Snow rates greatly
lower across the west Friday as the trough axis drifts over the
Rockies, but broad light to locally moderate snow persists over=20
much of the terrain. Most of the Rockies have over 30% probs for an
additional 6" on Day 3.


...Upper Midwest and Great Lakes...
Day 3...

As the upper trough crosses the southern Rockies Friday night into
Saturday, a strengthening southwesterly oriented jet streak across
the Plains places the Upper Midwest in the favorable left-exit=20
region over an inverted surface trough. Potent axis of 700 mb WAA=20
may allow for additional lift beginning across the Upper Midwest=20
Friday before sliding eastward into Lower Michigan by Saturday=20
morning. Current WPC probabilities for >4" are around 20% over=20
eastern Neb and western IA with >6" probs of 30-60% mainly over
southern WI and much of the L.P. of MI. Dynamic banding is forecast
with this re-developing wave and guidance has variability in
placement, so further details on heavy snow banding will come into
better agreement in subsequent shifts.


Jackson




...Winter Storm Key Messages are in effect for both the Northeast
and West as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-bEaK6Cpp0K9O90p20q8XUzhJ9QNgt-dmEUHgKAl2MUfh= _Lvoug8qC7uPV-8PxWliXSB4qghi_yKuMeE2rRkeHqD994$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-bEaK6Cpp0K9O90p20q8XUzhJ9QNgt-dmEUHgKAl2MUfh= _Lvoug8qC7uPV-8PxWliXSB4qghi_yKuMeE2rRkoz19Vdk$=20

$$

=3D =3D =3D
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FOUS11 KWBC 060913
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 AM EST Thu Feb 6 2025

Valid 12Z Thu Feb 06 2025 - 12Z Sun Feb 09 2025

...Pacific Coast through the Northern Rockies...
Days 1-2...

...Winter Storm to impact the West as a potent low tracks across=20
California tonight, and the northern Rockies on Friday...

A stormy pattern across the West will finally come to an end late=20
this week as the upper level pattern resets to a much drier pattern.=20
In the upper levels, the previous cutoff low centered near=20
Washington State will rejoin the main jet stream and open up into a=20
potent trough. This upper level low has quite a bit of shortwave=20
energy circulating around it. This shortwave energy will support=20 cyclogenesis off the California coast. The surface low will track=20 northeastward over California and into Idaho, before transferring=20
its energy to a leeside low over Colorado. The upper level trough=20
will be weakening through late Friday night, however the surface low=20
will tap into quite a bit of Pacific moisture which will be moving=20
into the Pacific Northwest. The low-turned-trough will start out=20
positively tilted but as it moves into the interior Pacific=20
Northwest, it will become more neutrally tilted as its energy merges=20
with the jet stream it is rejoining.

NAEFS continues to show this system will have a significant Pacific=20
feed of moisture with more than 500 kg/ms of Integrated Vapor=20
Transport, which still tops the 99th percentile. Snow levels will=20
rise ahead of the low but lower both behind it and to the north of=20
the track. NBM snow levels into Oregon and Idaho will be around=20
3,000 ft. Into the southern Sierras, snow levels will rise to above=20
8,000 ft through the first half of Thursday night, then will drop to=20
around 5,000 ft through midday Friday behind the cold front. For the=20 northern Sierras, snow levels will stay between 6,000 and 8,000 ft.=20
WPC probabilities for the Sierras are low to moderate (30-50%) for=20
snow amounts above 24 inches. Into far northern California,=20
probabilities are moderate to high (50-70%) for snowfall amounts of=20
over 12 inches. While snow levels will be lower, there will not be=20
nearly as much moisture available to convert to snowfall.

=46rom late Thursday night into Friday morning, the snow will spread=20 northeastward into Idaho, Montana, and Wyoming. This will occur as=20
the upper level shortwave trough forcing the surface low causing the=20
snow lifts to the northeast and continues weakening. Meanwhile, a=20
1030+ mb Arctic High will remain in place from Alberta and=20
Saskatchewan and into the Northern Plains. This high will supply=20
plentiful cold air to keep all of these areas as snow. Once again=20
however, plentiful moisture from the warm side of the system will=20
follow the cold conveyor belt into the northern Intermountain West,=20
allowing for plenty of moisture for widespread snow. The greatest=20
snow in this area will be into the Sawtooths of Idaho, Bitterroots=20
of Montana and into the Wind River Range and Yellowstone/Teton N.P.=20
areas of Wyoming. WPC probabilities in this area are moderate (40-
60%) for 12 inches or more of snow through Saturday morning.

WSSI values will get into the Extreme range (substantial disruptions=20
to daily life and very difficult to impossible travel) for the=20
southern Sierras with the heaviest snow today into tonight. Moderate=20
to major impacts (Disruptions to daily life and avoid travel) are=20
expected from the Klamath mountains of northern California into=20
southern Oregon as well as through the Sawtooth and Wind River=20
Ranges.

Wegman


...Northern Plains through the Great Lakes and Ohio Valley...=20
Days 1-3...

A fairly potent shortwave trough can be seen over the southern
Canadian Parries moving eastward with robust ascent focused within
the diffluent axis of the trough. Lift is currently strongest=20
across Northern MN into the Arrowhead north of Lake Superior.=20
Forecast is for the disturbance to continue advancing eastward with
the strongest forcing centered over Western Ontario into the U.P.=20
of Michigan by the morning. Additional snow accumulations >4" are=20
likely in-of the central and eastern side of the U.P. with the=20
latest WWD probs ranging between 50-80% within the corridor south=20
of Superior. Small section of elevated probs (40-70%) also exists=20
within the Keweenaw Peninsula as well, a combination of synoptic=20
based forcing with the potent shortwave, as well as some lingering=20
lake effect later this afternoon.=20

After a brief respite on D1 across the Northern Plains and Upper
Midwest, the progressive flow across much of the CONUS will surge=20
another winter storm system eastward into the Northern Plains to=20
begin mid-D2. This system is progged to be much more impressive as
a potent driving trough ejects from the Pacific Northwest and into
the Northern Plains late-Friday night into Saturday morning. The=20
overall mid- level pattern across the Northern Plains is progged to
remain generally flat, but rapid height falls and a potent=20
subtropical jet streak reaching 155kts will help push IVT=20
exceeding the 90th percentile from NAEFS into the region. At the=20
same time, strengthening WAA downstream of a low pressure moving=20
across the Central Plains will draw higher moisture poleward, and=20
the overlap of this WAA with the LER of the upper jet streak will=20
produce a stripe of impressive 850-600mb fgen, efficiently lifting=20
ascent into a deepening DGZ. This will result in a swath of snow=20
from the Dakotas through Wisconsin, with an embedded band of=20
heavier snow likely mainly intersecting the enhanced 700mb
frontogen being depicted within all viable deterministic as of 00z.
Spread has decreased among the deterministic with impressive probs
for >6" being depicted by the National Blend (70-90%). Consensus
among ensembles within the 00z GEFS/ECENS combo suggest high=20
confidence for this event and impactful snow is likely across the=20
Dakotas, especially northeastern SD and into Minnesota/Wisconsin.=20
WPC probabilities have remain elevated given the latest trends,=20
and now support a high risk (>70%) for more than 6 inches D2 over
northeast SD through south-central MN and central WI, surrounded=20
by a larger expanse of 40-60% from north-central SD through east-=20
central WI. High probs >70% continue into D3 with emphasis over=20
central WI over to the Lake Michigan shores, including the Green=20
Bay area to the southern portion of the Door Peninsula.

Farther to the southeast, the WAA will lift a warm nose more=20
robustly immediately downstream of the surface low into the Upper=20
Midwest and Ohio Valley. This will cause a stripe of mixed=20
precipitation to develop on D3 from Illinois through eastern Ohio,=20
and WPC probabilities increase once again, now featuring a 40-70%=20
chance for at least 0.01" of ice over central IL through much of=20
the northern half of OH.

Weiss/Kleebauer


...Mid-Atlantic and Northeast...=20
Days 1-3...

Progressive moving shortwave analyzed over southern IL/LN will
continue moving to the east-northeast with several smaller mid-
level perturbations ejecting downstream of the mean trough. At the
surface, cyclogenesis in-of Cape Hatteras has transpired with the
expected low to progress rapidly to the northeast with modest
strengthening as it approaches LI and Southern New England by
later this morning. Further north, a formidable 1030mb high will
continue to shunting eastward with the previous cold air filtering
shutting off with prevailing easterlies likely occurring east of
the Piedmont creating a textbook case of WAA nosing through a very
shallow cold air mass. By morning, mixed precipitation will be the
dominant ptype over the Northern Mid Atlantic with the depth of the
cold air hanging on across New England and Upstate NY where snow
will remain the primary ptype through the front part of D1. Higher
elevations across New England will be the last areas to see any
changeover from snow to IP/ZR, or at least have significantly
degraded snow ratios due to the acceleration of warm air poleward
into the area as southwesterly flow within the 850-650mb layer
contributes to the mixed precipitation phases during the first half
of the period. Maturation of the surface cyclone off the coast of
New England should help maintain the cold air long enough within
the confines of interior ME and Northern New England where snow
will maintain the ptype through the period before the system moves
out into the North Atlantic during the back half of the forecast.
WPC probabilities for >4" remain elevated (40-70%) within those=20
higher terrain areas of the Tug Hill, Adirondacks, Green and White=20
Mtns., and the Southwest terrain over ME. Ice accumulations have
trended fairly low with some prospects of 0.01-0.1" of ice
accretion over much of PA through the Hudson Valley of NY and
Southern New England. These areas should remain outside warning
criteria, but there will still be some lingering hazards within
those locales that receive any ice accretion.=20

A sharp cold front will maneuver through the Northeastern U.S. by
D2 creating a locally enhanced zone of LES off Lake Ontario with
the primary fetch settled between flow between 270-290 deg.
creating a persistent band between Oswego up towards Pulaski and
areas downstream. The southern portion of the Tug Hill will be the
benefactor of the LES development with general persistence in the
band as it oscillates within that narrow corridor. Considering
delta-T's nearing 20C off the lake behind the strong CAA regime,
the band EL's between 15-20k ft will be sufficient for producing
rates between 1-2"/hr at peak intensity within the band offering a
narrow stripe of 6+" during the D2 time frame before the flow
settles and the band falls apart. WPC probs within the anticipated
axis is between 40-60% for >4" with a very small area of ~70% just
downwind of the Lake near Pulaski.=20

Finally by D3, a potent shortwave trough across the Plains and
Midwest will continue to advancement eastward with a surface low
spawning on the southern periphery of the trough axis across KS/MO,
quickly moving east-northeast during the D2 into D3 period. A
strong southwesterly WAA regime within the 850-600mb layer will
transpire once again, only this time will generate a much more
significant outcome of snowfall into New England. Very strong
850-700mb frontogenesis will accompany the setup with a deep enough
entrenched cold airmass over the Hudson Valley up through New
England to support a significant snowfall back over the region.
Surface low over the plains will move into the Ohio Valley with an
expected surface low transfer off the Delmarva coast creating a
prevailing east to northeast flow within the PBL that should create
enough of a barrier for the WAA pattern further south penetrating
much further than the NY state line across southeastern NY state.
This has been signaled among much of the latest deterministic with
a fair amount of ensemble support for this synoptic evolution. WPC probabilities are very robust for >4" with 70+% encompassing all of
Western NY state through Central NY and the Hudson Valley. The
higher probs extend well east into all of Southern New England with
80% probs focused just to the west of the Boston Metro. Probs for

8" are sufficiently within the 40-70% range across the Hudson

Valley with the epicenter of the highest probs located over the
Catskills and the Berkshires of western MA. Lower probs for at=20
least 4" also exist over a large area surrounding the above zones,=20
so there is a growing potential for an impactful snowfall occurring
during the D3 time frame which includes much of Saturday into=20
Sunday morning.=20

Ice potential will also exist further south as the CAD wedge over
the Mid-Atlantic will likely see repeating setup with WAA within
the PBL causing issues concerning ptype transition from frozen to
liquid hydrometeors. Similar to this past setup, areas northwest of
the fall line in the Mid-Atlantic within the Piedmont will have the
best chance for ice accretion after a short instance of SN/IP as
the storm enters mid-D3. Highest probs for >0.1" of ice accretion
still exists over the Laurel Highlands down into Western MD
(40-60%), the same areas that are currently contending with ice
this evening. It remains a fluid situation as guidance has not
settled on the timing of the mixed phase to predominantly liquid
ptype, but impacts are anticipated to be very similar to what is
currently occurring.=20

Kleebauer


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!49ZkWMFzJGHZmEDM90fqINVl_hfDN1vlQBkcwIKACSPQZ= f-903UL6c1SJef3KhaTON_aq4-BL-X47jYy2jPkA2_w-QA$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!49ZkWMFzJGHZmEDM90fqINVl_hfDN1vlQBkcwIKACSPQZ= f-903UL6c1SJef3KhaTON_aq4-BL-X47jYy2jPk8Sd9W_c$=20

$$

=3D =3D =3D
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FOUS11 KWBC 061937
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
237 PM EST Thu Feb 6 2025

Valid 00Z Fri Feb 07 2025 - 00Z Mon Feb 10 2025

...Pacific Coast through the Northern Rockies...
Days 1-2...

...Winter Storm impacting the West as a potent low tracks into the
Pacific Northwest tonight and the northern Rockies by Friday...

A stormy pattern across the West will finally come to an end late=20
this week as the upper-level pattern resets to a much drier=20
pattern. A cutoff low centered near Washington State will rejoin=20
the polar jet and open up into a potent (but less anomalous)=20
trough. An associated surface low off California coast will move
ashore tonight, tracking northeastward into northern
California/Nevada, southwest Oregon, and into Idaho by Friday
morning (eventually transitioning to a leeside low over Colorado
this weekend). The upper level trough will be weakening through=20
late Friday night, however the surface low will tap into quite a=20
bit of Pacific moisture which will be moving into the Pacific=20
Northwest. The low- turned-trough will start out positively tilted,=20
but as it moves into the interior Pacific Northwest it will become
more neutrally tilted as it is fully absorbed into the polar jet.=20

Global model initializations (12z Thu runs) depict significant a=20
significant feed of moisture off the Pacific with more than 500=20
kg/ms of Integrated Vapor Transport (IVT), which still tops the=20
99th percentile (per NAEFS climatology). Snow levels will rise=20
ahead of the low, but lower both behind it and to the north of the=20
track. NBM snow levels into Oregon and Idaho are indicated to be=20
between 3-4k ft. Into the southern Sierras, snow levels will rise=20
to above 8k ft through the first half of Thursday night, then fall=20
to around ~5k ft through midday Friday behind the cold front. For=20
the northern Sierras, snow levels will stay between 6-8k ft for the
bulk of the snowfall, falling to between 3-5k ft by Friday morning
(as snowfall begins to taper off). WPC probabilities for the=20
Sierras are moderate to high (50-70%) for snow amounts above 24=20
inches through mid-day Friday. Into far northern California,=20
probabilities are moderate to high (50-70%) for snowfall amounts of
over 12 inches for the same time period. While snow levels will be
lower, there will not be nearly as much moisture available to=20
convert to snowfall (as the IVTs are focused farther south of the
front).=20

=46rom late tonight into Friday morning, the snow will spread=20
northeastward into Idaho, Montana, and Wyoming as the shortwave and
associated surface low pivot to the northeast (while generally
weakening). Meanwhile, a 1030+ mb Arctic High will remain in place
from Alberta and Saskatchewan and into the Northern Plains. This=20
high will supply plentiful cold air to keep all of these areas as=20
snow. Plentiful moisture from the warm side of the system will=20
follow the cold conveyor belt into the northern Intermountain West, facilitating widespread snow. The greatest snow in this area will=20
be into the Sawtooths of Idaho, Bitterroots of Montana and into the
Wind River Range and Yellowstone/Teton N.P. areas of Wyoming. WPC=20 probabilities in this area are moderate to high (50-70%) for 12=20
inches or more of snow through late Saturday night.

WSSI values will get into the Extreme range (substantial disruptions=20
to daily life, travel not advised) for the southern Sierras with=20
the heaviest snow through tonight. Moderate to major impacts=20
(considerable disruptions to daily life, avoid travel if possible)
are expected from the Klamath mountains of northern California=20
into southern Oregon as well as through the Sawtooth and Wind River
Ranges.=20

Churchill/Wegman


...Northern Plains through the Great Lakes and Ohio Valley...=20
Days 1-3...

A potent shortwave will eject from the interior Northwest Friday
evening and begin to race east within flat/progressive flow=20
entrenched across the CONUS. This shortwave trough will remain=20
positively tilted through its evolution across the region, but=20
have plenty of vorticity and accompanying PVA to produce impressive
omega. This will additionally be enhanced by a potent subtropical=20
jet streak exceeding 150kts which will both additionally enhance=20
deep layer lift but also enhance IVT (progged to exceed the 90th=20
percentile of the CFSR climatology into the Plains/Upper Midwest).

This moisture will be additionally enhanced by a surge of
WAA/isentropic ascent, especially along the 285-295K surfaces,
downstream of the parent shortwave. This WAA will manifest as well
as a stripe of enhanced fgen, especially within the 700-600mb
layer. This will additionally improve ascent, and there is likely
to be a region of intense omega driving heavy snowfall rates as the
system moves rapidly eastward. At the same time, the DGZ is progged
to deepen considerably in response to this WAA, which is reflected
by SREF DGZ 100mb depth probabilities reaching 50% from eastern SD
through the Twin-Cities of MN and into central WI. With the column
being quite cold, this could result in fluffy and efficient
dendrites that can accumulate rapidly. However, it should be noted
that the best fgen lies at the top of this DGZ, so may not really
manifest as an efficient "cross-hatch" signature for snow growth,
and with the column so cold large aggregates will be difficult to
achieve. Still, an above-climo SLR seems likely, and snowfall rates
of 1-2"/hr should be supported within this translating swath of
snow.

The progressive nature of the system combined with the slightly
less than ideal snow growth, will somewhat limit total snowfall,=20
but this will still be an impactful event, and in some areas may be
the heaviest snowfall of the season to date. Current WPC=20
probabilities are 50-70% for 6+ inches across central MN and into=20
western WI D2, with generally 3-6" expected on either side of the=20
core of this snowfall from SD into MI.

Farther to the southeast, the WAA will lift a warm nose more=20
robustly immediately downstream of a developing surface low into=20
the Upper Midwest and Ohio Valley, primarily after 12Z Saturday. This
will cause a stripe of mixed precipitation to develop from=20
Illinois through eastern Ohio, resulting in another round of
accumulating sleet/freezing rain across these areas. WPC
probabilities for 0.01" of ice are moderate (50-70%) from eastern
IL through eastern OH, with locally more than 0.1" possible
(10-30%) in IN/OH.

Weiss


...Mid-Atlantic and Northeast...=20
Days 1-3...

The first in a series of winter weather events will be exiting=20
this evening as a coastal low moves progressively eastward from New
England. As this low departs this evening, it will continue to toss
moisture back to the west on cyclonic flow, resulting in areas of
still moderate snowfall across eastern New England and much of
Maine. However, the progressiveness of the mid-level pattern will
keep this system moving quickly away from the area, and snowfall
associated with it should end before daybreak Friday. Additional
accumulations of 2+ inches is likely across northern Maine as shown
by WPC probabilities reaching 50-70% in the higher elevations.

Behind this low, a potent cold front will race quickly southeast in
its wake, leading to pronounced CAA and briefly impressive low-
level convergence. This will have a two-pronged impact to winter
weather across the Northeast. The first will be an increased threat
for convective snow showers and snow squalls Friday morning,
especially across Upstate NY and into Northern New England.
Although the timing of the front is not ideal for impressive
squalls, there is forecast to be enough overlap of low level RH,
fgen, and instability to support scattered to widespread convective
snow showers and isolated squalls. This is supported by simulated
reflectivity in the high-res CAMs as well as HREF probabilities
showing low-end chances for 1+"/hr rates. Accumulations with any
squalls will be minor, but briefly heavy rates and lowered
visibility could cause hazardous travel.

Then behind this front, CAA causes a drop in 850mb temperatures to
support sfc-850mb delta T nearing 20C across Lake Ontario (Lake
Erie is now completely ice covered). EL's approaching 15,000 ft
over Lake Ontario will help support a single band of lake effect
snow (LES) with rates at times reaching 1-2"/hr beginning Friday=20
aftn and persisting into Saturday aftn, with some upstream=20
connection to Lake Huron aiding in the threat. This will likely=20
lead to some heavy snowfall accumulations, especially across the=20
Tug Hill Plateau, where WPC probabilities for 4+ inches of snow D1
are above 70%, with an additional 30% chance on D2, leading to LES
total snowfall as much as 12 inches in isolated areas.

A more significant system begins to take shape the latter half of
D2. Despite the generally flat and progressive flow across the=20
CONUS, a potent shortwave trough ejecting from the Plains will move
into the Ohio Valley by 00Z/Sun, and then continue rapidly east
across New England on Sunday. This will be accompanied by an
impressive upper jet streak progged to reach 170kts as it arcs
across the northern tier of the CONUS. Downstream and to the south
of this overlapping synoptic ascent, a wave of low pressure will
begin to develop along a warm front as it lifts northward in
response to intensifying WAA, leading to an expansion of
precipitation late D2 and moreso on D3 from the Ohio Valley
northeast through the Mid-Atlantic and into New England.

High pressure ahead of this developing low will retreat to the east
Sunday, with the resultant isentropic ascent maximizing along the
290-300K surfaces. Mixing ratios within this lift are quite
impressive, 4+g/kg, which will push a plume of PWs exceeding the=20
90th percentile according to the NAEFS climatology into the Mid-=20
Atlantic and Southern New England. As this low skirts east off the=20
NJ coast, it will likely intensify south of New England, and the=20
resultant ageostrophic flow and CAA in its wake will halt the=20
progression of the accompanying warm nose, keeping mixed=20
precipitation confined to the Mid-Atlantic states. While there is=20
still quite a bit of latitudinal uncertainty in the placement of=20
this low and accompanying WAA strength, confidence is increasing=20
that a significant winter storm will move quickly across the region
D3.=20

This will result in a swath of moderate to heavy icing, generally
across the Central Appalachians and Mid-Atlantic states where WPC=20
probs for more than 0.1" of ice are above 70% (10-30% for 0.25" in
the Laurel Highlands and MD Panhandle). Farther north, however,=20
the threat for heavy snow has substantially increased as impressive
850-600mb fgen overlaps with the ridge of elevated theta-e to=20
support heavy snow rates and possible banded structures.
Despite the fast moving system, WPC probabilities are high (>70%)
for 6+ inches from near the Capital District around Albany eastward
to the Boston metro area and SW ME. Locally double-digit snowfall
is possible, especially across the Worcester Hills of MA and=20
Monadnock Region of NH.


Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!8uswbG8gYMDREyMueqYQhRYN3Huw1YZN74yT0gXaQzU2c= v4ESSKr6mytq3kALRGYf5TJZ4rqo_wIQDAyeKtnPpi6HMg$=20

$$

=3D =3D =3D
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FOUS11 KWBC 130856
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EST Thu Feb 13 2025

Valid 12Z Wed Feb 12 2025 - 12Z Sat Feb 15 2025


...Great Lakes and Northeast...=20
Day 1...

Low pressure moving through the Ohio Valley this morning will=20
continue northeastward into southeastern Ontario, with broad WAA-=20
driven snow over northern New England D1 and an icy mix where=20
boundary layer sub-freezing temperatures persist beneath the=20
warming layer ~750-850mb (e.g., North Country, Green and White=20
Mountains). By this afternoon, a forming area of low pressure near=20
the Gulf of Maine will help maintain a colder column over much of=20
Maine, favoring more snow for the Pine Tree State via northerly=20
flow. After 00Z, the whole system will depart into Atlantic Canada.
WPC snowfall probs for >4" are highest (>50%) in the higher=20
elevations of the Adirondacks and Green/White Mountains, as well as
over the northern half of Maine. Freezing rain probs for >0.1" ice
are low (10-20%) over parts of central New England.

In its wake, NW/WNW/W flow across the mostly unfrozen Great Lakes=20
will support lake effect snow as 850mb temps of -15 to -20C move=20
across the region. WPC probabilities for >6" low (10-50%) over the=20
eastern U.P. of MI but are high (>70%) south of Buffalo with some=20
moisture flux through the ice and especially southeast off Lake=20
Ontario just north of SYR up to FZY. Snowfall totals locally over a
foot are possible.


...Sierra Nevada, Pacific Northwest through the Rockies...=20
Days 1-3...

...Atmospheric River with heavy Sierra Nevada snow affects=20
California tonight into Friday. Key Messages are linked below...=20

Upper low approaching 130W this morning is directing an=20
atmospheric river (AR) into NorCal then shifts south down the coast
to SoCal tonight as the low opens/splits into a slow-moving=20
trough.

The atmospheric river has IVT around 500 kg/m/s (near the MAX in=20
the CFSR climo period) making for a wave of moderate to heavy=20 topographically- enhanced precip over the Sierra Nevada. Snow=20
levels around 6000-7000ft across CA this morning will drop back to=20 5000-6000ft under the trough axis tonight (Sierra) and around=20
4500ft (Shasta/Trinity). SLRs will be low to moderate given the=20
strong WAA, resulting in plenty of Sierra cement (>5ft and perhaps=20

8ft at the highest peaks). Snowfall rates will lessen into early=20

Friday (as SLRs rise a bit) and end completely by Friday night as=20
upper ridging builds in.

The lingering cold air brings light lowland snow and icing=20
potential for southern WA through western OR. Freezing rain threat=20
will advance northward on the edge of the precip shield this=20
morning from western OR (Coastal Ranges) northward across the=20
Columbia River into southwestern WA. WPC probs for >0.1" are=20
moderate (40-80%) for mainly the Coast Ranges west of the=20
Willamette Valley.=20

Moisture quickly spreads east throughout the Intermountain West=20
through Friday ahead of the slow-moving trough axis. Moisture=20
transport into the Great Basin and Wasatch/Rockies will be notable=20
per the ECMWF EFI and NAEFS IVT percentiles >99th percentile. WPC=20
probs for >8" are above 80% for the Tetons through the Wasatch and=20
Tushar Mtns (UT) and across the western slopes of the CO Rockies=20
with >60% probs for the Sawtooths of ID, and Kaibab Plateau in AZ=20
and northern NM ranges. Snow rates peak early Fri from west to east
as the trough axis drifts over the Rockies, but broad light to=20
locally moderate snow persists over much of the terrain into early=20
Sat (end of D2). By Sat/D3, the last piece of the broad longwave=20
trough will slip through the central Rockies, yield another several
inches of snow centered over western CO where WPC probs for at=20
least 6 inches are moderate (40-70%).

Finally, a sprawling North Pacific system will enter the PacNW at=20
the end of D3 with generally light snow for the WA Cascades.


...Upper Midwest/Great Lakes/Northeast...=20
Days 2-3...

Leading edge of the western trough Friday afternoon will manifest=20
itself at the poleward exit region of a 140kt upper jet across the=20
Plains and near the equatorward entrance region of the northern=20
stream jet across southern Ontario. This will promote broad lift=20
over the Upper Midwest with accompanying WAA atop an inverted=20
surface trough. Quick westward flow aloft will keep the system=20
moving through the region, but potential exists for a quick-hitting
few inches of snow with room for some localized bands of heavier=20
snow across WI. WPC probs for >4" snow are >50% over much of=20
central and southern WI to the IL border and into Lower MI.=20

Farther east into D3, snow will expand into the Northeast on=20
continued WAA ahead of a deepening upper trough and strengthening=20
upper jet arced from the Lower MS Valley to the St. Lawrence River=20
Valley. Light to moderate snow is forecast across southern Ontario=20
eastward into NY and New England where WPC probs for >4" snow are=20
moderate (40-70%), especially above 1500ft or so. Across the=20
interior Mid-Atlantic, cold surface temperatures from the departing
high pressure will be overrun with WAA precip, resulting in areas=20
of freezing rain from the southern Appalachians northward through=20
the Laurel Highlands into the Catskills. WPC probs for at least=20
0.1" icing are moderate (40-70%) with low-end (10-30%) probs for at
least 0.25" icing. This will depend on how strong the southerly=20
flow will be to scour out the cold surface temperatures vs precip=20 timing/onset and intensity.=20


Fracasso/Jackson


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!47RfJ0KrfWibvV9EriQLY0K0ysz7t3npsK2kq7S3BR1Al= 8Dt0CWum4y07uzoHXi54d007yUsgZXZcIFST14Vy9IqwC4$=20

$$

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FOUS11 KWBC 132116
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 PM EST Thu Feb 13 2025

Valid 00Z Fri Feb 14 2025 - 00Z Mon Feb 17 2025


...New York State and New England...=20
Day 1...

Heavy synoptically forced snow shifts east of northern Maine tapers
off rest of this afternoon.

Westerly flow over Lake Erie is producing lake enhanced snow over
the Chautauqua Ridge in spite of Erie being nearly frozen over per
GLERL. However, as flow shifts WNWly this evening, flow over
Superior, Georgian Bay, and Lake Ontario will produce single
banding LES along the Oswego/Onondaga county lines through Friday
morning. Day 1 snow probs in that specific swath just north of
Syracuse for >8" are over 70% with localized totals over 12"
likely.


...Sierra Nevada, Pacific Northwest through the Rockies...=20
Days 1-2...

...Heavy Sierra Nevada snow continues into Friday with heavy snow
over the central/southern Rockies into Friday night. Key Messages=20
are linked below...

Upper low over northern CA is directing the AR over SoCal this
evening with continued onshore flow into Friday with instability
enhancing precip over the Sierra Nevada as the low opens into a
slow moving trough. Snow levels drop back to 5000-6000ft under the
trough axis tonight (Sierra) and around 4500ft (Shasta/Trinity)
helping add more wet snow. Day 1 snow probs for additional >18" are
60-90% along the High Sierra.

Cold air lingers over the PacNW lowlands with continued snow and
freezing rain, particularly around Portland (especially west of
town in the Coastal Range) tonight. Day 1 ice probs for an
additional >0.1" after 00Z are 20-30% there.=20

Moisture continues to spread east through the Intermountain West=20
through Friday evening ahead of the slow-moving trough axis.=20
Snow rates peak tonight over the Wasatch and Tushar in Utah and
western CO Rockies slopes. Day 1 snow probs for >12" are over 80%
for these areas and around 50% for the OR Cascades, western
Sawtooths, Tetons, and Kaibab Plateau.

Day 3...

The next upper low approaches western Washington Sunday with snow
levels around 3000ft for the northern Cascades. Day 3 snow probs
for >8" are 30-60% for this higher terrain.


...Upper Midwest/Great Lakes/Northeast...=20
Days 2-3...

Shortwave trough ejecting from the western trough crosses the
central Plains Friday with an inverted trough spreading up through
Wisconsin Friday night. Thump of snow with this inverted trough is
on warm air advection, but sufficient cold air is there to allow
heavier snow with >10:1 SLRs over much of WI Friday night. Day 2
snow probs for >4" are 50-80% across southern and eastern WI and
the northern 2/3 of the L.P. of MI. There are >6" probs inn the
40-60% with the key here the rates Friday night.=20

Starting Friday night, the SWly jet from the southern Plains
through the Northeast intensifies to over 150kt by 00Z Sun. Snow=20
expands across the Northeast on continued WAA ahead of the=20
deepening upper trough Saturday/Saturday night. Day 3 snow probs
for >4" are 40-90% over Upstate NY and northern New England with 50
to 70% probs for >8" over the Adirondacks up through the northern
NY border, Greens, Whites, and much of Maine. Much like the system
ending today, there has been some shifts north with the low, so the
swath of heavy snow is yet to be determined. The rapidly deepening
low Sunday will add wind impacts over Northeast.



Jackson



...Winter Storm Key Messages are in effect for a winter storm
impacting the west into Saturday before intensifying over the
Northeast Saturday night and Sunday...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!9ysNhU6XgSXCE4Dcv9ZjBwwKfq-FbUVcRVj7NG69ZE5Px= czRIztQHvlGPz35jd814h8jFGV2dWbT4q21JTqCawzVtuw$=20

$$

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FOUS11 KWBC 070818
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
318 AM EST Fri Feb 7 2025

Valid 12Z Fri Feb 07 2025 - 12Z Mon Feb 10 2025

...Pacific Coast through the Northern/Central Rockies...
Days 1-2...

Active period of winter weather continues over the next few days
throughout the West as a potent area of low pressure progresses
across the Intermountain West and Rockies through early Saturday,=20
while onshore flow continues throughout the Pacific Northwest in=20
concert with a cold airmass in place.

Low pressure currently analyzed entering the OR High Desert early
this morning is expected to track into ID today and drag along IVT
up to the 99th climatological percentile within areas of snowfall
per the 12z NAEFS. The northern precipitation shield extending
across OR, ID, and the northern Rockies will be mainly associated
with strong mid-level WAA through tonight before the upper trough
begins to shear within fast-zonal flow across the north-central
United States. Snow levels are expected to be around 3,000-5,000ft
throughout central ID, western WY and far southwestern MT, with
much lower snow levels just to the north within the arctic airmass
intruding from western Canada. Precipitation is also ongoing across
the Sierra Nevada this morning, but should come to an end by this
afternoon. WPC probabilities for at least 6 inches are high (>70%)
on D1 across the Sawtooths of ID and from the Wasatch Mts of UT=20
through the western ID and southwest MT ranges. These high probs=20
also extend into the northern CO ranges on D2 as upslope flow
enhances with the approaching cold front.

Elsewhere, weak area of low pressure moving onshore the PacNW early
D2 is expected to spread light snow and snow showers throughout the
region where deep cold air remains in place. This results in snow
levels outside of the immediate coast under a few hundred feet. WPC probabilities D1-D2 for at least 4 inches of snow are high=20
(60-90%) across the Cascades.


...Northern Plains through the Great Lakes and Ohio Valley...=20
Days 1-2...

As the potent shortwave exits the Northern Rockies Friday evening=20
and begins to race east within flat/progressive flow entrenched=20
across the CONUS, a west-east oriented band of snowfall is forecast
to spread across the north-central United States. This shortwave=20
trough will remain positively tilted through its evolution across=20
the region and has trended flatter/weaker over the last few
forecast cycles, but still falls within a favorable jet streak
environment and associated PVA to produce impressive omega. This deep
layer lift as well as enhanced IVT (progged to exceed the 90th=20
percentile of the CFSR climatology into the Plains/Upper Midwest).

This moisture will be additionally enhanced by a surge of
WAA/isentropic ascent, especially along the 285-295K surfaces,
downstream of the parent shortwave. At the same time, the DGZ is=20
progged to deepen considerably in response to this WAA, which is=20
reflected by SREF DGZ 100mb depth probabilities reaching 50% from=20
the SD-ND border through central MN and into central WI. With the=20
column being quite cold, this could result in fluffy and efficient=20
dendrites that can accumulate rapidly. However, it should be noted=20
that the best fgen lies at the top of this DGZ, so may not really=20
manifest as an efficient "cross-hatch" signature for snow growth,=20
and with the column so cold large aggregates will be difficult to=20
achieve. Still, an above-climo SLR seems likely, and snowfall rates
of 1-2"/hr should be supported within this translating swath of=20
snow.

The progressive nature of the system combined with the slightly
less than ideal snow growth, will somewhat limit total snowfall,=20
but a swath of 4-8 inches still appears likely. The weaker/flatter
upper shortwave has lead to a slight northward trend with recent
guidance and will need to be monitored for short term mesoscale
trends. Current WPC probabilities are 50-70% for 6+ inches across=20
central MT just to the north of Billings. These probs then lower
over the High Plains before increasing again near in the northern
Plains/Upper Midwest. D1-D2 WPC probabilities for at least 6 inches
are low (10-20%) along the ND-SD border and increase to medium
(30-60%) across central MN and central WI as better jet dynamics
increase lift over this region. This stripe of snow will also
extend into the L.P. of MI Saturday afternoon, with 30-50% probs of
6+ inches.=20

Farther to the southeast, the WAA will lift a warm nose more=20
robustly immediately downstream of a developing surface low into=20
the Upper Midwest and Ohio Valley, primarily after 12Z Saturday. This
will cause a stripe of mixed precipitation to develop from=20
Illinois through eastern Ohio, resulting in another round of
accumulating sleet/freezing rain across these areas. WPC
probabilities for 0.01" of ice are moderate (40-70%) from eastern=20
IL through eastern OH, with locally more than 0.1" possible=20
(10-30%) in IN/OH.


...Mid-Atlantic and Northeast...=20
Days 1-3...

Behind a strong low deepening in far eastern Canada, a potent cold
front will race quickly southeast in its wake, leading to=20
pronounced CAA and briefly impressive low- level convergence. This=20
will have a two- pronged impact to winter weather across the=20
Northeast. The first will be an increased threat for convective=20
snow showers and snow squalls Friday morning, especially across=20
Upstate NY and into Northern New England. Although the timing of=20
the front is not ideal for impressive squalls, there is forecast to
be enough overlap of low level RH, fgen, and instability to=20
support scattered to widespread convective snow showers and=20
isolated squalls. This is supported by simulated reflectivity in=20
the high-res CAMs as well as HREF probabilities showing low-end=20
chances for 1+"/hr rates. Additionally, current radar observations
and a recent Snow Squall Warning issued across western NY confirms
the ingredients for convective pockets of snow are in=20
place. Accumulations with any squalls will be minor, but briefly=20
heavy rates and lowered visibility could cause hazardous travel.

Then behind this front, CAA causes a drop in 850mb temperatures to
support sfc-850mb delta T nearing 20C across Lake Ontario (Lake
Erie is now completely ice covered). EL's approaching 15,000 ft
over Lake Ontario will help support a single band of lake effect
snow (LES) with rates at times reaching 1-2"/hr beginning this=20
aftn and persisting into Saturday aftn, with some upstream=20
connection to Lake Huron aiding in the threat. This will likely=20
lead to some heavy snowfall accumulations, especially across the=20
Tug Hill Plateau, where WPC probabilities for 4+ inches of snow D1=20
are above 70%, leading to LES total snowfall as much as 12 inches=20
in isolated areas.

A more significant system begins to take shape on D2. Despite the=20
generally flat and progressive flow across the CONUS, a potent=20
shortwave trough ejecting from the Plains will move into the Ohio=20
Valley by 00Z/Sun, and then continue rapidly east across New=20
England on Sunday. This will be accompanied by an impressive upper=20
jet streak progged to reach 170kts as it arcs across the northern=20
tier of the CONUS, with New England anticipated to be located in
the left-exit region for favorable upper divergence and increased
ascent. Downstream and to the south of this overlapping synoptic=20
ascent, a wave of low pressure will begin to develop along a warm=20
front as it lifts northward in response to intensifying WAA,=20
leading to an expansion of precipitation on D2 from the Ohio Valley
northeast through the Mid- Atlantic and into New England.

High pressure ahead of this developing low will retreat to the east
Sunday, with the resultant isentropic ascent maximizing along the
290-300K surfaces. Mixing ratios within this lift are quite
impressive, 4+g/kg, which will push a plume of PWs exceeding the=20
90th percentile according to the NAEFS climatology into the Mid-=20
Atlantic and Southern New England. As this low skirts east off the=20
NJ coast, it will likely intensify south of New England, and the=20
resultant ageostrophic flow and CAA in its wake will halt the=20
progression of the accompanying warm nose, keeping mixed=20
precipitation confined to the Mid-Atlantic states. There remains
some uncertainty along the northern and southern fringes of the
snowfall forecast, with QPF the question for northern New England,
and ptype the question along southern New England. However, in
between there is increasing confidence in a swath of heavy=20
snowfall (around 5-8 inches on average) from Upstate New York=20
through much of New England. Despite the fast moving system, WPC=20 probabilities for at least 6 inches of snow are high (70-80%) from=20
the southern Adirondacks eastward to the Boston metro area and=20
neighboring portions of southern VT/NH.


Additionally, a swath of moderate to heavy icing is expected
across the Central Appalachians and Mid-Atlantic states as a warm
nose quickly leads to sleet/freezing rain as the predominant ptype
within the climatologically favorable CAD regions. WPC probs for=20
more than 0.1" of ice are above 80% (20-40% for 0.25" in the Laurel
Highlands and MD Panhandle), with 50-70% 0.1" probs extending
across northern MD and southern PA.


Snell/Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!8Mcz21ov-ED5vn5crYdqIY0EE57hKWu8jpO6r6s-0uScM= 4grhvTHU5ASAJU3hn0r4eLZm-YSw4M0CbktAvqdd8ce6yI$=20

$$

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FOUS11 KWBC 071824
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
124 PM EST Fri Feb 7 2025

Valid 12Z Fri Feb 07 2025 - 12Z Mon Feb 10 2025

...Pacific Coast through the Northern/Central Rockies...
Days 1-2...

The end of this active wintry period is finally in sight, but some
lingering periods of heavy snowfall will continue through the first
half of the upcoming weekend. As the more potent of two upper level
troughs track east this evening, periods of heavy mountain snow are
anticipated from the Bitterroots, Tetons, Bear River, and Wasatch
ranges on east through the Big Horns on south to the central=20
Rockies of southern Wyoming and Colorado through tonight. This is=20
largely due to the strong upper-level ascent via jet streak=20
dynamics aloft paired with IVT values (200-300 kg/m/s) that are=20
above the 99th climatological percentile. Most of the snowfall will
have concluded by Saturday morning (excluding the central=20
Rockies). WPC probabilities show the Tetons, Wasatch, and central=20
Rockies having high chances (>70%) for receiving >4" of snowfall
through Saturday morning with the taller and more remote peaks of
the Colorado Rockies sporting low-to-moderate chances (30-50%) for

8" of snow.

Farther west, another upper level trough will track through the
Pacific Northwest with snow levels below 500ft in many cases
tonight and into Saturday. This would allow for some light snow
accumulations along the I-5 corridor, while <10th climatological
percentile 500-700mb heights could support steeper lapse rates that
result in some snow squalls (particularly east of the Cascades)
during the day. This upper trough is generally moisture-starved,
however, which should limit snowfall amounts to lighter overall
totals. WPC probabilities show some portions of southwest WA and
far northwest OR along the windward sides of the Cascades that
sports moderate-to-high chances (40-70%) for snowfall totals >6".
Otherwise, most areas will likely witness snowfall totals of 1-4"
through Saturday afternoon with the lesser-end of that range most
likely for communities along I-5. This upper trough will produce
some light snow Saturday night across portions of the northern
Rockies, but totals will pale in comparison to the snowfall the=20
region has witnessed over the past 5-7 days. Minor accumulations=20
of generally 2-6" in the Blue, Bitterroot, and Lewis Ranges are=20
forecast through Saturday night before snow tapers off on Sunday.


...Northern Plains through the Great Lakes and Ohio Valley...=20
Days 1-2...

Fast moving but significant storm system will bring a stripe of
heavy snow to the Northern Plains and Upper Midwest, with mixed
precipitation including freezing rain impacting the Ohio Valley.

This system will spawn from a potent but positively tilted
shortwave emerging from the Northern Rockies this evening. This=20
shortwave will traverse quickly to the east as flow across the=20
CONUS remains predominantly flat and progressive, lifting across=20
the Northern Plains by Saturday morning, and into the Great Lakes=20
Saturday evening. Despite the modest amplitude of this feature,
which has trended flatter the past several runs, it will work in
tandem with the favorably placed left exit of a 150 kt jet streak
to produce a brief period of intense ascent from west to east.
Additionally, this jet streak will help surge IVT into the area,
and combine with increasing 285-295K isentropic ascent to produce=20
elevated PWs favorable for moderate to heavy snowfall.

The WAA from the south accompanying this isentropic ascent
downstream of the shortwave will help to deepen the DGZ, and the
SREF probabilities are above 90% for 100mb of depth, which could
support impressive snowfall rates approaching 1"/hr as progged by
the WPC prototype snowband tool. With the wave being generally flat
and fast, and the most impressive fgen lying at the top of the DGZ,
ascent within the best snow-growth region won't maximize
efficiently for the most intense snow rates leading to heavy
snowfall accumulations. However, SLRs should still generally be
above climo in the cold column, and with rates around 1"/hr at
times in the translating fgen band, a stripe of heavy snow
exceeding 6" still appears likely from MN through WI as reflected=20
by WPC probabilities of 50-70% within this axis.

Farther to the southeast, especially after 12Z Saturday, the WAA=20
downstream of a developing surface low will push a warm nose into=20
the Upper Midwest and Ohio Valley. This will occur in conjunction
with the expanding precipitation shield, leading to a stripe of=20
mixed precipitation from Illinois through eastern Ohio. There is
high confidence in this mixed precipitation region, although some
uncertainty continues in the exact p-type transition. Still, the
mixture of sleet and freezing rain will create ice accumulations
that could exceed 0.1" as reflected by WPC probabilities across OH
and IN reaching 10-30%.


...Mid-Atlantic and Northeast...=20
Days 1-3...

A potent cold front will be offshore New England to start the
period, leaving pronounced CAA in its wake. 850mb temps falling to
around -15C within this CAA will help steepen lapse rates across
Lake Ontario (Lake Erie is now frozen) to support increasing
instability and rising inversion levels. Unidirectional W to NW
flow across Lake Ontario within this environment is supportive of a
single band of heavy lake effect snow (LES), focused along and
south of the Tug Hill Plateau and just north of the Finger Lakes
region. Snowfall rates of 1-2"/hr are likely within this band until
it erodes Saturday afternoon, leading to snowfall accumulations for
which WPC probabilities indicate have a 50-70% chance of exceeding
4 inches.

As the LES wanes, a much more significant system begins to approach
from the west as a potent shortwave embedded within generally zonal
flow across the CONUS races towards the region. By 18Z Saturday
/late D1/ this shortwave will be moving across WI/MI/IL,
accompanied by a 150kt upper jet streak. Some interaction of this
upper level ascent with a warm front draped across the Mid-
Mississippi Valley will help spawn a wave of low pressure in the
lower Ohio Valley. As this low begins to consolidate, downstream
WAA will intensify and manifest as 290-295K moist isentropic=20
ascent surging northeast reflected by mixing ratios exceeding
4g/kg. This will produce PWs that may briefly exceed the 97.5th
percentile of the CFSR climatology according to NAEFS, highest into
the Central Appalachians and Mid-Atlantic to start D2.

During this evolution, precipitation will rapidly expand as
southern stream and northern stream energy begins to interact
across the Mid-Atlantic states. This will provide increased ascent
across the region, and a plume of snow, sleet, and freezing rain
will overspread from the Ohio Valley and Central Appalachians
northeastward. The impressive accompanying WAA will push a warm
nose steadily northward through 06Z Sunday, so even though many
areas, especially north of the Mason Dixon line, will begin as a
burst of snow, p-type should transition pretty rapidly to sleet and
then freezing rain, eventually changing to rain Saturday night in=20
lower elevations south of I-80. Snowfall rates may be briefly=20
heavy before transition, but icing could be more problematic as=20
reflected by WPC probabilities for 0.1+" of ice that reach 50-90%=20
in the Central Appalachians D1, extending northeast at 30-50% D2 as
far as central PA and in the vicinity of Washington, D.C.

As the parent shortwave continues to track progressively to the
east, the accompanying forcing and moisture will also pivot with
it, and secondary low pressure development is likely off of the NJ
coast late Saturday night into Sunday morning. This low will become
dominant and intensify as zonal but modestly coupled jet structures
interact with a baroclinic zone offshore. As this low deepens and
moves almost due east south of New England, it will cross near the
Benchmark (40N/70W), leading to a substantial snow event for=20
Upstate NY, the Poconos, and at least Southern New England (SNE),=20
although there remains uncertainty into how far north (or south)=20
the heaviest snow will spread. As the low deepens and pulls away to
the east, a renewed surge of cold air both through the=20
ageostrophic flow into the low and the subsequent CAA in its wake=20
will limit the progress of the warm nose, while dry air to the=20
north noted in regional soundings inhibits PWs from aggressively=20
lifting towards Canada. In between, an axis of heavy snow is likely
as strong WAA produces impressive 850-600mb fgen, producing strong
ascent into the DGZ. The overlap of this strong fgen with some
theta-e lapse rates approaching 0C/km suggests banding potential=20
from Upstate NY into SNE, and with elevated SLRs, snowfall rates of
1-2"/hr appear likely. Total snowfall will be limited by the speed
of this system as it will only snow in most areas for 12-18 hours,
but this will result in heavy accumulations, and WPC probabilities
D2 for more than 6 inches of snow are high (>70%) from near Albany,
NY eastward into MA, southern VT, and southern NH. Locally 8-12" of
snow is possible in some areas.

As this low pulls away Sunday afternoon and drying occurs rapidly
in its wake, snowfall will wane quickly late D2. However, renewed
CAA behind the accompanying cold front will again setup an
environment favorable for LES E/SE of Lake Ontario. Shifting winds
(more N early, becoming more W late D3) will likely cause multi-
bands along and south of Lake Ontario into the Finger Lakes region,
before organizing into a more significant single band late in the
forecast period back into the Tug Hill Region. Confidence in the
exact location is low at this time, but WPC probabilities do
feature a moderate risk (30-50%) for 2+ inches of snow southeast of
Lake Ontario.


Weiss/Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-Xxue8cfXOBtDeS3FJAiUcE0YqZTWFjJd7tgEEaEIuYtH= KAmTu-W7SKdISLWy5j3FZrf52HyHrj2xcNA5U2i7Ab5MRo$=20

$$

=3D =3D =3D
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FOUS11 KWBC 080753
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Sat Feb 8 2025

Valid 12Z Sat Feb 08 2025 - 12Z Tue Feb 11 2025

...Pacific Northwest and Northern/Central Rockies...=20
Day 1...

The end of this active wintry period is finally in sight across the
mountainous West, but some lingering periods of heavy snowfall=20
will continue today. An upper level trough will track through the=20
Pacific NW with snow levels starting below 500ft in many cases on=20
D1 before rising gradually. This would allow for some light snow=20 accumulations along the I-5 corridor early this morning, while=20
<10th climatological percentile 500-700mb heights could support=20
steeper lapse rates that result in some snow squalls (particularly=20
east of the Cascades) during the day. This upper trough is=20
generally moisture- starved, however, which should limit snowfall=20
amounts to lighter overall totals. WPC probabilities are medium
(40-60%) for much of the Cascades for snowfall totals >6".=20
Otherwise, most areas will likely witness snowfall totals of 1-4"=20
through this afternoon with the lesser- end of that range most=20
likely for communities along I-5. This upper trough will also=20
produce some light snow tonight across portions of the northern=20
Rockies, but totals will pale in comparison to the snowfall the=20
region has witnessed over the past 5-7 days. Minor accumulations of
generally 2-6" in the Blue, Bitterroot, and Lewis Ranges are=20
forecast through today before snow tapers off on Sunday.
Additionally, continuing light to moderate snowfall is expected
early this morning across the CO Rockies as a cold front oozes
southward across the Rockies and contributes to favorable upslope
flow and low chances for an additional 6 inches of snow above
9000ft.


...Upper Midwest through the Great Lakes and Ohio Valley...=20
Day 1...

Ongoing storm system will bring a stripe of heavy snow to the Upper
Midwest and Great Lakes region, with mixed precipitation including
freezing rain impacting the Ohio Valley.

Positively tilted shortwave crossing the northern Plains today is
the driving force for an east-west swath of snow D1 from central MN
and central WI through the northern L.P. of MI. This shortwave=20
will traverse quickly to the east as flow across the CONUS remains=20 predominantly flat and progressive. Despite the modest amplitude=20
of this feature, it will work in tandem with the favorably placed=20
left exit of a 150 kt jet streak to produce a brief period of=20
intense ascent from west to east. Additionally, this jet streak=20
will help surge IVT into the area, and combine with increasing=20
285-295K isentropic ascent to produce elevated PWs favorable for=20
moderate to heavy snowfall.

The WAA from the south accompanying this isentropic ascent
downstream of the shortwave will help to deepen the DGZ, and the
SREF probabilities are above 90% for 100mb of depth, which could
support impressive snowfall rates approaching 1"/hr as progged by
the WPC prototype snowband tool. With the wave being generally flat
and fast, and the most impressive fgen lying at the top of the DGZ
(around 700 mb), ascent within the best snow-growth region won't=20
maximize efficiently for the most intense snow rates leading to=20
heavy snowfall accumulations. However, SLRs should still generally=20
be above climo in the cold column, and with rates around 1"/hr at=20
times in the translating fgen band. WPC probabilities (beginning=20
12z Saturday) show a high chances (60-80%) of heavy snow exceeding=20
6" from central WI through the northern L.P. of MI.

Farther to the southeast the WAA downstream of a developing=20
surface low will push a warm nose into the Midwest and Ohio=20
Valley. This will occur in conjunction with the expanding=20
precipitation shield, leading to a stripe of mixed precipitation=20
from central IL through eastern Ohio. There is high confidence in=20
this mixed precipitation region, although some uncertainty=20
continues in the exact p-type transition. Still, the mixture of=20
sleet and freezing rain will create ice accumulations that could=20
exceed 0.1" as reflected by WPC probabilities across northern OH=20
and IN reaching 10-30%.


...Mid-Atlantic and Northeast...=20
Days 1-2...

After a day of modest CAA and surface high pressure shifting
directly over the Northeast to start the D1 period, a significant
winter storm begins to approach from the west as a potent=20
shortwave embedded within generally zonal flow across the CONUS=20
races towards the region. By this afternoon the shortwave will be=20
moving across WI/MI/IL, accompanied by a 150kt upper jet streak.=20
Some interaction of this upper level ascent with a warm front=20
draped across the Mid- Mississippi Valley will help spawn a wave of
low pressure in the lower Ohio Valley. As this low begins to=20
consolidate, downstream WAA will intensify and manifest as 290-295K
moist isentropic ascent surging northeast reflected by mixing=20
ratios exceeding 4g/kg. This will produce PWs that may briefly=20
exceed the 97.5th percentile of the CFSR climatology according to=20
NAEFS, highest into the Central Appalachians and Mid- Atlantic.

During this evolution, precipitation will rapidly expand as
southern stream and northern stream energy begins to interact
across the Mid-Atlantic states. This will provide increased ascent
across the region, and a plume of snow, sleet, and freezing rain
will overspread from the Ohio Valley and Central Appalachians
northeastward. The very impressive accompanying WAA will push a=20
warm nose steadily northward through 06Z Sunday, so even though=20
many areas, especially north of the Mason Dixon line, will begin as
a burst of snow, p-type should transition pretty rapidly to sleet=20
and then freezing rain, eventually changing to rain Saturday night=20
in lower elevations south of I-80. Snowfall rates are likely to be
very impressive before transition from central/eastern PA to=20
northern NJ and Long Island. This is depicted well by the 00z HREF,
with non-zero chances for snowfall rates to exceed 2" per hour in
the 00z-06z Sun timeframe across from northern NJ to southern CT=20
and Long Island, including NYC. Icing could be just as problematic
in the Mid- Atlantic as reflected by WPC probabilities for 0.1+"=20
of ice that reach 50-90% in the Central Appalachians D1, extending=20
northeast at 30-50% D2 as far as central PA and in the vicinity of=20 Washington, D.C. northern suburbs. Probabilities for at least 0.25"
of ice reach 50-60% across western MD and the Laurel Highlands of=20
PA, where the greatest potential for tree damage and power outages=20
exist.

As the parent shortwave continues to track progressively to the
east, the accompanying forcing and moisture will also pivot with
it, and secondary low pressure development is likely off of the NJ
coast late Saturday night into Sunday morning. This low will become
dominant and intensify as zonal but modestly coupled jet structures
interact with a baroclinic zone offshore. As this low deepens and
moves almost due east south of New England, it will cross near the
Benchmark (40N/70W), leading to a substantial snow event for=20
Upstate NY, the Poconos, and at least Southern New England (SNE),=20
although there remains uncertainty into how far north (or south)=20
the heaviest snow will spread. As the low deepens and pulls away to
the east, a renewed surge of cold air both through the=20
ageostrophic flow into the low and the subsequent CAA in its wake=20
will limit the progress of the warm nose, while dry air to the=20
north noted in regional soundings inhibits PWs from aggressively=20
lifting towards Canada. In between, an axis of heavy snow is likely
as strong WAA produces impressive 850-600mb fgen, producing strong
ascent into the DGZ. The overlap of this strong fgen with some
theta-e lapse rates approaching 0C/km suggests banding potential=20
from Upstate NY into SNE, and with elevated SLRs, snowfall rates of
1-2"/hr appear likely. Total snowfall will be limited by the speed
of this system as it will only snow in most areas for 12-18 hours,
but this will still result in heavy accumulations. WPC=20
probabilities for more than 6 inches of snow are high (>70%) from
the Mohawk Valley of NY eastward into much of MA, southern VT,
southern NH, and the southeastern tip of ME. Locally 8-12" of snow
is possible in some areas.

As this low pulls away Sunday afternoon and drying occurs rapidly
in its wake, snowfall will wane quickly late D2. However, renewed
CAA behind the accompanying cold front will again setup an
environment favorable for LES E/SE of Lake Ontario. Shifting winds
(more N early, becoming more W D3) will likely cause multi- bands=20
along and south of Lake Ontario into the Finger Lakes region,=20
before organizing into a more significant single band late in the=20
forecast period back into the Tug Hill Region. Confidence in the=20
exact location is low at this time, but WPC probabilities do=20
feature a high risk (70-90%) for 4+ inches of snow southeast of=20
Lake Ontario.


...Central Rockies/Plains through the Ohio Valley and Central=20 Appalachians...=20
Day 3...

Next widespread wintry weather event to spread across the country
is expected to begin late D3 (Monday night) as shortwave energy at
the base of a longwave trough off the coast of southern CA gets
ejected eastward into the fast zonal flow dominating the upper
pattern across CONUS. In response, a strengthening 160kt jet streak
is forecast to stretch zonally from the southern Rockies to the
Northeast and shift eastward with time, placing areas from the
central Plains to the central Appalachians in the favorable right-
entrance region for enhanced upper divergence and lift. Current=20
WPC probabilities only go through 12z Tuesday, so values are low=20
(20-40%) for at least 2" of snow for the central Rockies, central=20
Plains, and central Appalachians, highest across the central=20
Rockies and central Plains. There is also likely to be a ribbon of=20
mixed ptype in the form of freezing rain/sleet, but not expected to
have large geographic coverage given weak relatively weak WAA and=20
not the coldest airmass in place at the surface. Current WPC=20
probabilities for at least 0.01" of freezing rain are low (10-30%)=20
and extend from north-central OK to the central/southern=20
Appalachians where CAD could elevate the freezing rain potential.

Snell/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!8EdOO-NonBmG1j8bXt3N9einCUmoijcwUO51Hm8qHueNi= DAnWJHJlNrAyG7sExV-Y-RwZXgXJPQYifJ3cwpxGqwAkWw$=20

$$

=3D =3D =3D
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FOUS11 KWBC 140845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Fri Feb 14 2025

Valid 12Z Fri Feb 14 2025 - 12Z Mon Feb 17 2025


...Central NYS...=20
Day 1...

WNW flow will continue a lake effect snow band off Lake Ontario=20
into the Syracuse metro this morning/afternoon and diminish later=20
this evening as it lifts northward. Day 1 snow probs for >4" are=20
40-90% in a narrow corridor.


...Sierra Nevada through the Rockies...=20
Days 1-2...

Atmospheric River has moved well inland, but the lagging upper=20
trough will continue onshore flow with instability enhancing precip
over the Sierra Nevada as the low opens into a slow-moving trough.
Snow levels have fallen back to 5000-6000ft under the trough axis=20
(Sierra) and around 4500ft (Shasta/Trinity) bringing light snow to=20
lower elevations. Snow should taper off later this evening from=20
west to east across CA. Day 1 snow probs for an additional 8" are=20 moderate(40-70%) across much of the Sierra.

Moisture has reached the Rockies with a strong influx from the SW=20
and the trough axis will pass the Four Corners early Sat, favoring=20
moderate to heavy mountain snow with gradually lowering snow levels
as colder air moves in. Snow rates will ease over the next 12-24=20
hours with additional snow over the Wasatch and Tushar in Utah and=20
western CO Rockies northward into the Tetons and eastward into the=20
San Juans and Sangre de Cristos. 48-hr snow probs for >12" are=20
over 80% for these areas.


...Pacific Northwest...
Days 2-3...

The next multi-vorticity lobe upper low in the northeast Pacific=20
will send a cold front into the Pac NW late Sat into early Sun.=20
Snow levels around 3000-4000ft for the northern-southern Cascades=20 (respectively) will give light to moderate snow to the passes that=20
continue into early Monday as the trailing main upper low finally=20
reaches the coast. WSW flow will spread moisture across eastern OR=20
into ID, western MT and western WY where the favored terrain will=20
see moderate snow totals. Cold temperatures over the northern Great Basin/northern Rockies will favor at least some snow to most=20
valley floors. 48-hr snow probs for >12" are >50% for this higher=20
terrain.


...Upper Midwest/Great Lakes/Northeast...=20
Days 1-3...

Eastward extension of the western trough will bring WSW flow to=20
the Upper Midwest later today with embedded vort maxes atop an=20
inverted surface trough. Thump of snow with this inverted trough is
on warm air advection, but sufficient cold air is there to allow=20
heavier snow with >10:1 SLRs over much of WI tonight. WPC snow=20
probs for >4" are >50% from southeastern MN across central WI. A=20
broader area of light snow is expected over much of the region,=20
setting up a somewhat prolonged but interrupted period of light=20
snow.=20

Into D2, the western trough will push into the Plains and start to
amplify in concert with the downstream upper jet (>160kts) across=20
the Great Lakes. Moisture will continue to spread eastward across=20
Lower Michigan, southern Ontario, then into the Northeast. With a=20
trend toward a slower/sharper upper system, QPF has increased over=20
much of the Midwest and into Lower Michigan where WPC probs for at=20
least 4 inches of snow on Sat are >50% over most of Lower Michigan,
but are at least 25% from southern Iowa and across northern IL. On
the eastern side, WAA will promote light snow over much of NY with
WPC probs for >4" snow highest over the Poconos into the=20
Catskills, but also at least 30% over the higher elevations above=20
1500ft or so. To the south, cold air at the surface along/east of=20
the Appalachians (NC through VA into central PA) will hang tough as
overriding precip from the west encroaches, favoring freezing rain
and perhaps some sleet on Saturday. With a sfc low track from the=20
Mid-South through OH, warm air will eventually win out due to=20
strong 50kt SW 850 flow. WPC probs for at least 0.10" icing are=20

50% over southwestern VA northward into central PA, where there=20

are also probs for >0.25" icing (30-50%).=20

By D3, the surface low is forecast to track from just west of PIT=20
toward western/central NY with some coastal redevelopment over=20
southeastern MA (Cape Cod) that may move into the Gulf of Maine. A=20
lot of details have yet to be resolved, but this scenario will=20
likely result in all snow close to the Canadian border where warm=20
air intrusion is least likely, a mix of snow to sleet/freezing rain
over much of the area between the I-90 and I-80 corridors, and=20
rain farther south and southeast as warmer air surges up the coast.
The timing of the many players will modulate the amount of each=20
ptype, but for now the highest probabilities for at least 8 inches=20
of snow are over the Adirondacks into northern VT/NH and interior=20
Maine. Several inches of snow are probable (40-60% chance) along ad
north of the I-86/Rt 17 to I-84 corridor (NY to CT). Icing is most
likely in areas that are able to stay coldest the longest,=20
including central PA, the Poconos, Catskills, and Berkshires where=20
WPC probs for at least 0.10" icing are >50%. Again, the details of=20
the system are still in flux which will influence where and as what
type the precipitation may fall.=20

Fracasso



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!7cZcrNiNyC013vxSdTP5K9sCdXMD7RyM9lVgFS2DPBrkp= JVXHMRkTsZ0dw0O7xkte1yApcVGbVWAtK3FVvP4MreODp8$=20

$$

=3D =3D =3D
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FOUS11 KWBC 142103
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
403 PM EST Fri Feb 14 2025

Valid 00Z Sat Feb 15 2025 - 00Z Tue Feb 18 2025



...Rockies...=20
Day 1...

The upper trough over the west will continue to dig through the=20
Four Corners tonight before ejecting east over the southern Plains
through Saturday. NWly jet on the back side of the trough will
shift over the Rockies Saturday. Generally moderate snow continues
over the Utah and CO Rockies tonight through Saturday with Day 1
snow probs for >8" generally 50-80% with snow levels dropping from
6000ft to 4000ft.


...Central Plains/Midwest/Great Lakes/Northeast...=20
Days 1-3...

...Winter storm shifts east through this weekend, with heavy snow=20
from the central Great Lakes through the interior Northeast with=20
areas of freezing rain for much of the Appalachians, northern Mid-=20
Atlantic and southern New England. See Key Message link below...

Shortwave impulses ejecting ENE on strengthening SW flow are
providing lift above a developing inverted surface trough over the
east-central Plains. Thump of snow from WAA ahead of this inverted
trough has brought a swath of light to moderate snow over IA/MN
that will lift over much of WI and northern IL this evening and
much of the L.P. of MI overnight. Enhancement of precip is=20
expected in banding as the jet approaches with local snowfall=20
rates reaching 0.5"/hr. Some narrow banding is likely to develop
farther southwest from eastern CO through Neb and central IA.=20

Day 1 snow probs for >4" are over 10% from northeast Neb through
much of WI and MI with over 30% probs for >6" over the southern
half of WI, increasing to around 60% by the western shore of Lake
MI.=20

Potent surface low development is expected over the Mid-South on
Saturday with well above normal moisture (see the WPC excessive
rainfall outlook for further info there and a developing comma head
over the Midwest Saturday night that further develops as it tracks
over the Northeast Sunday. Heavy snow bands can be expected in this
comma head north and on the back side of the low pressure system.=20

Warm air advection brings a wintry mix of snow to sleet to freezing
rain to some areas going plain rain over the Northeast Saturday
through Sunday. Saturday morning expect some freezing rain in the
central Appalachians at precip onset that may linger over WV/VA
through Saturday afternoon. Greater coverage of ice is expected
over much of PA and NY Saturday/Saturday night before spreading
over southern New England Sunday. Day 1.5 probs for >0.25" ice are
around 20% in the Allegheny Highlands of VA into WV and 50-70% over west-central PA over the Laurels and Allegheny National Forest. For
Day 3 these probs for >0.25" are 20-60% over the Poconos,
Catskills, Berkshires and even Worcester Hills in MA.

Heavy snow is most likely to persist over far northern NY, central
Mass and north through the Greens/Whites and much of Maine all over
50% for >6" on Day 2.5 with values over 80% along the northern NY
border and across the northern half of Maine for Day 3..


...Pacific Northwest/Rockies/Central Plains...=20
Days 2-3...

The next multi-vorticity lobe upper low in the northeast Pacific=20
will send a cold front into the Pac NW late Saturday. Snow levels=20
around 3000-4000ft for the WA/OR Cascades and Pacific moisture=20
will give light to moderate snow to the passes that continue
through Monday as the trailing main upper low finally reaches the=20
coast. Westerly flow spreads moisture across the northern Rockies
with low level northerly flow over the Plains from a 1040mb high
shifting south from the Canadian Prairies. Day 2 snow probs for >6"
are 50-80% over the Cascades and northern Rockies to the Tetons.
Day 3 snow probs for >6" expand down the OR Cascades, much of the
ID Rockies, western WY, and northern CO with 50-90% values.


Jackson


...Winter Storm Key Messages are in effect with a shift to the
Northeast this weekend...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!7DZfHVNQ4niKg-dAjdMLkaHfC3Ucm9MchzDBv9Uo8ALrR= FX2GRGtJW-CZtb1PAgC2T1UnYEy6I7y736-aE7v8_E7OwQ$=20

$$

=3D =3D =3D
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FOUS11 KWBC 081836
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
136 PM EST Sat Feb 8 2025

Valid 00Z Sun Feb 09 2025 - 00Z Wed Feb 12 2025

...Pacific Northwest and Northern/Central Rockies...=20
Day 1...

Trough axis over eastern WA/OR and northern NV this afternoon will
continue eastward through the northern Great Basin/Rockies, taking
the last of any organized precipitation with it. Cold temperatures
over the PacNW (700mb temp anomalies below the 10th percentile)=20
will favor snow levels down below 500ft and to the inland valley=20
floors, but precipitation will trend lighter overnight as heights=20
begin to rise over WA/OR which will limit any additional and=20
appreciable snow to the Cascades (and only a few inches at best).=20
=46rom the Blue Mountains eastward across northern ID into NW=20
Montana, snow this evening may be moderate at times in advance of=20
the trough axis and as additional PVA slips through from the NW.=20
Total additional accumulations there may range from a few inches to
perhaps >6" in the highest peaks. WPC probabilities for at least 4
inches after 00Z are highest above 3000ft in the OR Cascades and=20
above 4000-6000ft in and around northern ID. Farther south,=20
additional mid-level vorticity will slide through CO with some=20
orographic enhancement across the central Rockies above 9000ft or=20
so.=20


...Mid-Atlantic and Northeast...=20
Days 1-3...

Fast moving shortwave ejecting from the Great Lakes will remain=20
progressive as it pushes east into New England early Sunday morning
as it remains embedded within generally pinched/flat flow across=20
the CONUS. This shortwave moving east will interact with a potent=20 west-to-east oriented jet streak and a warm front draped from the=20 Mid-Atlantic into the Mid-Mississippi Valley to spawn a low=20
pressure off the coast of NJ by 06Z Sunday. This low will then=20
deepen as it translates almost due east, crossing near the 40N/70W=20
benchmark before pushing farther into the Atlantic. Increasing=20
290-295K isentropic ascent and accompanying WAA downstream of this=20
wave will help surge moisture northward into New England and=20
Upstate NY, resulting in an axis of mixed precipitation across the=20 Mid-Atlantic, and heavy snow for Upstate NY and New England.

As precipitation expands tonight across the Mid-Atlantic, it will=20
be accompanied by a warm nose reaching +2 to +3C shifting as far=20
north as Long Island. There remains uncertainty into how far north=20
this will track due to the low pressure development offshore and=20
its resultant return of cold air back to the south, but it appears=20
areas from near the Mason-Dixon line northward through I-80 and as=20
far as northern NJ will experience primarily a mix of=20
sleet/freezing rain after a period of snow early. This will result=20
in additional icing accretion, which has a high chance (70+%) of=20
exceeding 0.1" from the MD Panhandle through the Laurel Highlands,=20
with a 30% chance extending into northern MD and southern PA.

Farther north, the setup is favorable for a short (12-18 hours)=20
period of heavy snowfall. The impressive isentropic lift with=20
mixing ratios exceeding 4g/kg will drive moisture northward, while=20
the accompanying robust WAA produces impressive omega into the=20
column as 850-700 fgen slopes strongly northward. This will=20
effectively interact with the snow growth region, producing a swath
of 1-2"/hr snowfall rates translating E/NE tonight through Sunday=20
morning. Locally higher rates are possible as well as cross-=20
sections indicate a threat for CSI as theta-e lapse rates collapse=20
below 0C indicating instability near the DGZ. The duration of these
intense snowfall rates may be shortened, however, as the guidance=20
has become more insistent that a dry slot will pivot as far north=20
as I-90 across New England, which would result in less cloud ice=20
and potentially a cutoff of heavy snow with some freezing drizzle=20
and much lower SLR. Where this occurs, amounts will be more=20
limited, but some light icing on top of heavy snow will be just as=20 impactful. Despite some uncertainty, there is still high confidence
in a swath of 6-12" of snow across Upstate NY and southern/central
New England, with variations in SLR (higher north, lower south)=20
offsetting the lower QPF across central/northern New England. The=20
latest WPC probabilities have increased due to a trend upward in=20
QPF, and now exceed 90% for 6+ inches from near Albany, NY through=20
the southern Greens, Berkshires, Worcester Hills, Monadnock region=20
of NH, and towards far SW Maine. This includes the major metro=20
areas of Albany, Worcester, Boston, and Portland. Locally, 10-12"=20
of snow is possible, and major impacts are possible (>50%)=20
according to the WSSI-P.

As this low pulls away Sunday afternoon and drying occurs rapidly=20
in its wake, snowfall will wane quickly late D2. However, renewed=20
CAA behind the accompanying cold front will setup an environment=20
favorable for LES E/SE of Lake Ontario. Shifting winds (more N/NW=20
early, becoming more W late D2 into D3) will result in a shifting=20
band of LES. For D2, the most significant accumulations are likely=20
in the northern Finger Lakes region, where they have a 70-90%=20
chance of exceeding 4" near the lake shore, with D3 probabilities=20
for 4+ inches reaching 30-50% focused in the Tug Hill Plateau


...Central Plains through the Mid-Atlantic Days 2-3...

The next in this parade of systems across the CONUS begins to=20
develop late D2 /Monday evening/ as a shortwave trough ejects from=20
near Baja and then moves east into the Southern Plains by Tuesday=20
evening. This shortwave will remain embedded within a longwave=20
trough axis as it moves east through its evolution, but guidance is
insistent that it will weaken with time and remain a generally=20
flat feature as it pivots to the east. This is reflected in 500mb=20
height trends among the various ensemble systems showing a weaker=20
and faster trough with stronger ridging downstream suppressing this
impulse. Despite the modest mid-level ascent expected with this=20
shortwave (through PVA and downstream divergence), upper diffluence
will likely increase with time as a downstream jet streak=20
intensifies towards 150kts and arcs sufficiently poleward while=20
leaving its tail across the Central Plains and into the Lower MS=20
VLY by Tuesday evening. This will provide additional deep layer=20
ascent as the system organizes through D3.

Then beginning early D3 /Monday night/ isentropic ascent=20
downstream of this developing system becomes quite impressive,=20
surging moisture out of the Gulf northward into the Lower MS VLY,=20
TN VLY, and the Mid-Atlantic. 295-300K surfaces indicate that=20
mixing ratios will reach values as high as 6-8 g/kg, indicative of=20
an extremely moist environment, additionally reflected by NAEFS=20
ensemble tables forecasting PWs approaching the 97th percentile=20
within the CFSR database, highest along the Gulf Coast but=20
stretching north into the colder airmass. While there is still=20
quite a bit of uncertainty into the timing and track of the=20
developing system, and the guidance has trended south this aftn, a=20
large swath of precipitation will develop and expand bringing all=20 precip-types Tuesday. The flat, fast, and suppressed flow will=20
cause the moisture to translate more east than north, but this=20
should result in an axis of at least moderate snow, with the=20
greatest risk for significant snow from eastern KY through the Mid-
Atlantic region. WPC probabilities at this time are highest for 4+=20
inches in the higher elevations of WV/VA where they peak above 70%,
and locally 6+ inches of snow is possible. Elsewhere, WPC=20
probabilities for 2" are 30-50% across much of this area.=20
Additionally, light icing is probably in SW VA and far NW NC where=20
up to 0.1" of ice may accrete.

Weiss/Fracasso



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!9FQuy6w8JcBb94PqkHxDXn9FxnzYlP0po11teqmEZLFAs= 8sQha50Xstk-4ty1tmntMruOafb6DTXwENF-tFHu2UJoN8$=20

$$

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FOUS11 KWBC 150803
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Sat Feb 15 2025

Valid 12Z Sat Feb 15 2025 - 12Z Tue Feb 18 2025


...Rockies...=20
Day 1...

The upper trough centered across the Four Corners will continue=20
eastward today, with the last trailing vorticity pushing through=20
the CO Rockies this afternoon. Light to modest snow over the higher
peaks of CO into southeastern WY will diminsh through the day with
an additional 4-8+" likely and much lighter snow into the valleys=20
and Front Range.=20


...Corn Belt/Midwest/Great Lakes/Northeast...=20
Days 1-3...

Trough in the Rockies will exit today with a long extension to the
northeast into the Upper Midwest. Base of the trough will lag=20
through TX but additional height falls out of Canada will slow the=20
northern stream, alloiwing the trough to recongeal as it heads into
the Ohio Valley and then the Northeast. The setup will be broad=20
WAA-driven snow into the Great Lakes and Northeast but as the=20
trough sharpens and jet becomes more S-shaped along 80W, low=20
pressure will deepen and surge mild air far northward toward the=20
Canadian border, allowing snow to change to sleet/freezing rain and
just rain through Sunday with the main low into western NY. By=20
that time, a new area of low pressure will start to take shape and=20 eventually take over southeast MA into the Gulf of Maine,=20
essentially halting the northward surge in milder air into/through=20
New England as the low finall then lifts northeastward along the=20
Maine coast and into Atlantic Canada by early Monday.=20

For D1, strengthening jet across Michigan into Canada will act to=20
maintain snowfall over Lower MI today where WPC probabilities for=20
at least 4 inches of snow are >50% for the central/eastern 2/3rds.=20
Into the Northeast, WAA-driven snow will overspread the region this morning/afternoon where temperatures are cold. Could capitalize on
good WAA for this front-end thump of snow but strong southerly=20
surge will drive the mixed ptype zone northward from the Mid-=20
Atlantic later this afternoon into tonight. WPC probs for at least=20
4 inches of snow are highest (>50%) farthest north where the cold=20
air will hang on the longest -- north of I-90 into the Adirondacks=20
and Green Mountains as well as into the Berkshires and Worcester=20
Hills. To the south, temperatures are sub-freezing thanks to high=20
pressure overhead this morning but aloft it is near and just above=20
0C. Any snow will turn to sleet or more likely freezing rain from=20
across the Midwest and especially into the central Appalachians (SW
VA into central PA then up into the Southern Tier of NY). Ice=20
accumulation will depend on how long the cold surface temperature=20
can resist the strong surge in mild air from the south. WPC probs=20
for at least 0.25" icing are at least 30% along the WV/VA line=20
northward to the I-99/US 220 corridor.=20

Into D2, low pressure over southeastern OH will track=20
northeastward toward western/central NY by the afternoon as the=20
coastal low takes shape, which should stop the northward push of=20
the mix ptype zone but not before it may reach all the way to the=20
Canadian border (NY/VT) and into Downeast Maine. The remaining cold
air will be largely confined to northern Maine where WPC probs for
at least 6 inches of snow are >50% north of I-95. Ice=20
accumulations will be primarily over eastern NY and north of I-95=20
into New England, especially into the Berkshires and Monadnocks=20
where ice probs for at least 0.25" are at least 20%.=20

By D3, storm will be well out into the Atlantic but with a broad=20
cyclonic flow back across the Great Lakes, supporting lake-effect=20
snow off all the lakes but especially off Lake Ontario on WNW flow.
This could support a healthy single band into the northern SYR=20
suburbs from Oswego toward Rome/Utica where at least several inches
of snow are possible.=20


...Pacific Northwest/Rockies/Central Plains...=20
Days 1-3...

The next multi-vorticity lobe upper low in the northeast Pacific=20
will send a cold front into the Pac NW later today with snow levels
around 3000-4000ft for the WA/OR Cascades. With the upper jet=20
nosed into southern OR for the next two days or so, onshore flow=20
will continue to provide Pacific moisture to the region and into=20
the Great Basin/northern Rockies, overriding cold air on the east=20
side of the Divide. There, lower level convergence should enhance=20
snowfall over western MT D2 into D3 with two-day WPC snow=20
probabilities for >12" >70%. Snow into the Cascades will affect=20
the passes esp D1-2 until the trailing upper low finally reaches=20
the coast.=20

Farther southeast, moisture will spread back into the central/CO=20
Rockies with additional amounts of at least 6 inches likely by D3.=20
Onto the Plains, incoming vort maxes in the quick WNW flow atop=20
lower-level WAA will favor light snow stretching from western NE=20 southeastward toward the MS River Valley including much of KS. The=20
air mass will be fairly cold thanks to high pressure starting to=20
assert itself across southern Canada into the Dakotas, supporting=20
SLRs ~15:1. Through 12Z Tue, WPC probabilities for at least 4=20
inches of snow are 40-60% over the northern half of KS into=20
southern NE with more to follow.=20


Fracasso



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!88-PewK77Ur9LQ3bDMbolWcFPOOPt3JbpybhL-du-PAE9= G0-mE1kk-tfUKhgRYRKy0o4fX0a7nfggdpfTjViwTJcQp4$=20

$$

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FOUS11 KWBC 171936
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
236 PM EST Mon Feb 17 2025

Valid 00Z Tue Feb 18 2025 - 00Z Fri Feb 21 2025


...Great Lakes...=20
Days 1-2...

Impressive winter storm exiting into the Canadian Maritimes today
will leave cyclonic flow in its wake and across the Great Lakes.
This will promote continued CAA through D1, with 850mb temps
plummeting to as low as -25C (Lake Superior) and -20C over Lake
Ontario. This will support bands of lake effect snow (LES)
especially D1 during the most intense CAA before the mid-level flow
pattern relaxes downstream of a deepening trough centered over the
Northern Plains/Upper Midwest later Wednesday. The generally W/NW
flow will support heavy LES bands, likely in the form of single
bands within unidirectional shear, and strong ascent focused into
the low-level but deep DGZ will support heavy rates that could
reach 2-3"/hr at times D1, heaviest east of Lake Ontario where an
upstream moisture connection to Lake Huron will exist. These bands
should be prolonged and intense D1, leading to WPC probabilities
that are high (>70%) for more than 6 inches east of Lake Ontario
and the far eastern U.P. Although LES will wane during D2,=20
additional snowfall exceeding 4 inches is possible (30%) in these
same areas. Downstream of Lake Ontario, total snowfall of 1-2
feet is possible before LES winds down.


...Pacific Northwest through the Central Rockies...
Days 1-3...

Two rounds of moisture spreading inland through enhanced IVT will
spread wintry precipitation across much of the coastal and interior
West.

The period begins with a longwave positively tilted trough
extending from the interior Northwest through the Northern Plains.
This trough will deepen with time, diving into the Great Basin
Tuesday morning and then pivoting into the Four Corners by the end
of D1 as shortwave energy traverses through it. At the same time,=20
a stationary front will be aligned from inland WA state southeast=20
into the CO Rockies, as onshore flow from the Pacific spreads=20
inland and lifts isentropically producing some modest enhancement=20
of lift. Shortwave ridging expanding along the Pacific Coast late=20
D1 will cut off Pacific moisture by Wednesday morning, but a axis=20
of moderate to heavy snow is likely before this occurs, primarily=20
along the stationary front and into downstream terrain. WPC=20
probabilities are high (70-90%) for more than 6 inches in the=20
terrain above generally 3000 ft from the Sawtooth into the Tetons=20
and as far southeast as the Park Range of CO.

After a brief respite, a more pronounced system will approach the
Pacific Coast as a potent shortwave closes off over the Pacific
Ocean and sheds eastward. This feature is progged to come onshore
near the WA/OR border Wednesday evening, and there is good model
consensus in this evolution despite modest differences in
amplitude. The core of this trough coming onshore WA/OR will
manifest as impressive height falls as far south as central CA, and
as the downstream ridge erodes, this entire feature will elongated
and pivot into the Great Basin/Central Rockies by the end of the
forecast period. Modest jet level ascent through the development of
a jet streak rotating around the base of this trough will enhance
lift, but in general forcing is expected to be broad and driven
primarily by height falls through D2-D3. Despite that, some
enhanced IVT progged to exceed the 90th percentile within the CFSR
climatology will spread inland within WAA downstream of the trough
axis, leading to rising snow levels but enhanced wintry=20
precipitation prospects. During this time, WPC probabilities for
more than 6 inches climb above 30% in the Cascades D2, but with
snow levels climbing above pass levels, with additional moderate
chances (30-50%) for 6+ inches on D3 in the same general areas.


...Central Plains through the Mid-Atlantic States...
Days 1-3...

A significant winter storm begins tonight across the Central Plains
and then spreads almost due east to the Mid-Atlantic on Wednesday.
There is still considerable uncertainly as to how this evolves off
the coast Wednesday night, but at least moderate snow and
significant icing is likely for many areas.

The system begins to take shape tonight as a shortwave ejects from
the Four Corners and traverses to the east, reaching the Central=20
Plains Tuesday evening. This will occur just north of a surface
cold front that will surge south into Texas, and the interaction of
this impulse with the elevated baroclinic zone will help induce
some backing of the low-level winds, leading to enhanced moist
isentropic ascent emerging from the Gulf, especially along the
285-290K surfaces where mixing ratios will rise to 3-4 g/kg. At=20
the same time, a jet streak angled into the Northeast will leave
its favorable RRQ for ascent atop the region, resulting in an=20
overlap of synoptic and mesoscale ascent. With moisture continuing=20
to surge into the region, this will result in an expanding axis of=20
heavy snow, especially from eastern KS and OK into northern AR,
southern MO, and western TN/KY. Here, the overlap of ascent and
moisture will combine with a deepening DGZ (SREF probs for 100mb of
depth exceeding 70% Tuesday evening and Tuesday night, resulting in
an axis of heavy snowfall. Additionally, a secondary jet streak
intensifying downstream of the sharpening trough will produce an
environment supporting modestly coupled jet streaks, and the
resultant ageostrophic response to the already impressive fgen will
likely (>80% chance) drive snowfall rates to 1-2"/hr as shown by
both HREF probabilities and the WPC prototype snowband tool.

This system will become increasingly progressive to the east, but
an 18-24 hour period of moderate to heavy snow with fluffy SLRs in
the cold environment will support rapid and significant snowfall
accumulations, especially Tuesday night from the Central Plains
into the western Tennessee Valley. Here, WPC probabilities for
more than 8 inches reach as high as 70%, with locally 12+ inches
possible in the vicinity of the most intense banding. South of this
heavy snow, an axis of mixed sleet and freezing rain is likely,
with locally more than 0.1" of ice possible (30%), highest across
southern AR.

This shortwave begins to race eastward towards the Mid-Atlantic
Wednesday as it gets squeezed into more zonal flow downstream of a
more impressive northern stream trough (500mb heights falling below
the 2.5 percentile anomaly according to NAEFS) digging out of the=20
Northern Plains. This is where the the forecast begins to get more
challenging. This northern stream trough will dive southeast
towards the Ohio Valley while continuing to deepen into a potent
closed low, resulting in downstream (south/east) jet development
which will intensify beyond 150 kts. The overlap of the impressive
height falls and LFQ of this jet streak will drive pronounced
ascent into the Mid-Atlantic states, concurrent with continued
moist isentropic lift from the Gulf into the area. This suggests
that after a modest "break" in intensity of precipitation in the
vicinity of the central Appalachians, renewed heavy precip will
develop, especially as secondary surface low pressure develops
offshore.

There has been a steady trend in guidance to keep this
precipitation suppressed south across the Carolinas and Virginia,
with the most uncertainty now involving the speed and placement at
which the secondary low develops and moves northeast up the coast.
With the southern stream less amplified and faster, phasing of
energy is progged to occur much later which should spare the
northern Mid-Atlantic and Northeast much if any snow. However,
heavy snow and mixed precipitation is still likely from eastern
TN/KY into NC and VA, with a swath of the heaviest snow most
likely across eastern VA. There is still a lot of uncertainty,
however, and clusters indicate the primary EOF is dependent on the
amplitude of this trough, with the GEFS members appearing to be a
bit under-dispersive with a flatter wave, while the EC/CMC are a
bit deeper in general. However, these deeper waves are also
generally slower, again suggesting the threat for a phased major
winter event are quite low.=20

However, with the low eventually deepening rapidly offshore, a=20
potent deformation axis collocated with the greatest moisture will=20
result in heavy snow accumulations, for which WPC probabilities=20
indicate a high risk (70-90%) for 6+ inches centered along the=20 Norfolk/Virginia Tidewater region. Surrounding this maximum, WPC=20 probabilities for 4 or more inches are 10-30% from eastern KY=20
through WV and east towards coastal Delaware and far northern NC.=20
Southeast of the snow, a mix of sleet and freezing rain is=20
expected, and freezing rain potential has increased beneath the=20
warm nose lifting northward. WPC probabilities for 0.1" peak above=20
70% D2 into D3 in parts of eastern and southeastern NC, with=20
locally 0.25-0.35 inches of ice possible.=20


Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!61uyEcFGG2mhbmpbK41-RYzUYY-t9gpiwDFhlNCjM0ALO= YlI-0m1WzVHjnsIDgZT2eEPce6SKoqCNmbYxpTHo16Awgo$=20

$$

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FOUS11 KWBC 180811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 AM EST Tue Feb 18 2025

Valid 12Z Tue Feb 18 2025 - 12Z Fri Feb 21 2025


...Great Lakes...=20
Days 1-3...

Cyclonic flow over southern Canada and the Great Lakes on the=20
western side of the elongated upper trough axis will favor a=20
continuation of the lake effect snow for the next couple of days.=20
With 850 temperatures in the -20sC and NW to WNW flow, multi-bands=20
will form off the Upper Lakes with a strong single band off Lake=20
Ontario with an impressive multi-lake moisture feed. THe pattern=20
will be slow to unfold, but by early Wednesday a closed low will=20
begin to form over the Corn Belt which will help disrupt the=20
pattern enough to diminish the lake effect snow, but then those=20
height falls will bring in a general/light snow to the region on=20
Thursday. WPC probabilities for at least 8 inches of snow over the=20
next two days are near 50% over the eastern U.P. of Michigan. Over=20
central NY between ROC-FZY-SYR, the strong single band will=20
continue to dump snow at 1-3"/hr rates with significant=20
accumulation in a narrow swath -- perhaps more than 12-18 inches=20

60% probs). By day 3, snowfall will be light with most areas=20

seeing less than 4 inches of snow.


...Pacific Northwest through the Central Rockies...
Days 1-3...

Height falls over the Great Basin this morning will continue=20
southeastward today, giving some additional snow to the CO Rockies.
To the north, additional height falls out of Canada will drop=20
through central MT with some light snow to the central ID ranges,=20 southwestern MY, and the western WY ranges where WPC probabilities=20
for at least 6 inches of snow are low (<40%) to the north but high=20

70%) over western WY and the high peaks of the northern CO=20

Rockies.=20

By day 2, a Pacific system will start to move into the Northwest,=20
spanning the latitudes from NorCal up to the Canadian border. IVT=20
will be modestly high (~90th percentile) into NorCal/southern=20
OR/northern NV toward Idaho, supporting light to moderate snows for
the terrain with snow levels near 3000ft to the north and 5000ft=20
to the south that will rise a bit as the core of the moisture plume
pushes through. The system will move steadily along and clear the=20
coast with QPF starting early Thursday, pushing into northern=20
UT/southern ID and into the Rockies. However, moisture will wane=20
and snow will become lighter overall into D3 with the snow confined
mainly to the Unitas and higher CO Rockies by then. For the 3-day=20
period, WPC probabilities for at least 8 inches of snow are highest

70%) over the higher terrain above 6000ft closer to the coast,=20

7000-8000ft over the Great Basin, and 9000ft over CO/WY.=20


...Central Plains through the Mid-Atlantic States...
Days 1-2...

A significant winter storm is underway over the Central Plains=20
which will spread eastward through the Mid-South into the southern=20 Mid-Atlantic with potentially major impacts including heavy snow=20
and significant ice.=20

Snow is already underway across KS into MO this morning, driven by
lead shortwaves ahead of the Rockies trough. Through this morning,
as the stronger height falls approach the region, snow will expand
over the central and southern Plains eastward beneath the RRQ of=20
the upper jet and atop the Arctic air mass driven in by the strong=20
cold front overnight. With sufficient moisture influx from the=20
Gulf, snow rates will increase over southern KS into southern MS=20
later this morning into the afternoon with >1"/hr rates at times=20
per the WPC snowband tool and HREF probs. Snow will advance=20
eastward into the Mid-South later this evening and overnight but=20
likely diminish somewhat in intensity. To the south, the shallow=20
Arctic air mass will continue southward but southerly flow aloft=20
will maintain >0C temperatures, favoring a mix of sleet and=20
freezing rain over parts of OK into AR, northern LA, and western=20
MS. For the D1 period, WPC probabilities of at least 4 inches of=20
snow are high (>70%) from southeastern KS and northeastern OK=20
eastward to western KY. Within this region, probabilities of at=20
least 8 inches of snow are >60% near Joplin to Springfield, MO.=20
Icing to the south should generally be light but there is a low=20
change (10-30%) of at least 0.10" accretion near the Oachita=20
Mountains in AR.=20

By Wednesday morning, the next phase of the system will take shape
over the northern Gulf as the entrance region of the upper jet=20
touches the LA/MS coast, helping to favor cyclogenesis. The=20
northern part of the system will still spread snow across the Mid-
South eastward to the central Appalachians where some orographic=20
lift will help wring out several inches of snow into eastern=20
KY/southern WV/southwestern VA. The larger QPF-maker will be the=20
forming Gulf low that is forecast to track ENE to NE across north=20
FL before turning northeastward along the Gulf Stream just off the=20
SC/NC coasts. With the cold air mass in place through the East,=20
this sets up a southern slider snow event with an axis of heavy=20
snow along the VA/NC border into the Tidewater and southern=20
DelMarVa. The incoming northern stream upper low will lag behind=20
just enough to not phase until farther downstream, but enough=20
ingredients will be coming into place in the formative stages of=20
this system to yield a modest to heavy snowfall for parts of the=20
southern Mid-Atlantic, with a cutoff near a line along I-66/I-95=20
into southern NJ. WPC probabilities for at least 6 inches of snow=20
are highest over southeastern VA and northeastern NC, squarely=20
through the Norfolk area.

Like places farther west, the >0C air aloft will rise up and over=20
the cold surface temperatures over eastern NC, setting up a=20
freezing rain event that may be significant along and east of I-95
between the VA border and into northeastern SC. There, WPC=20
probabilities for at least 0.10" icing are >50% with some areas=20
receiving more than 0.25" accretion.=20


...Southeastern Mass...
Day 3...

The exiting system from the Southeast/southern Mid-Atlantic will=20
track northeastward, and may clip southeastern MA/Cape Cod D3 on=20
its way into Atlantic Canada. The question revolves around the=20
speed of the incoming northern stream upper low and how much it can
capture the exiting system. Given the uncertainty leading into the
event in the Southeast/Mid-Atlantic, there are still a wide range=20
of solutions from zero to moderate snow over part of the region.=20
For now, there are low (10-40%) probabilities of at least 4 inches=20
of snow over Cape Cod and the Islands.=20


Fracasso


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!92kKkwbOehKBV2BtOiSCq2THIYORCAmTDDpxygk-jF7Q0= 5Y6P3T0r05kbzgsuHmq3WS3DKk8WDp5dXVNWHc5cX6IEaA$=20

$$

=3D =3D =3D
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FOUS11 KWBC 181953
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 PM EST Tue Feb 18 2025

Valid 00Z Wed Feb 19 2025 - 00Z Sat Feb 22 2025


...Central Plains through the Mid-Atlantic States...
Days 1-2...

A significant winter storm is underway over the Central Plains=20
which will spread eastward through the Mid-South into the southern=20 Mid-Atlantic with potentially major impacts including heavy snow=20
and significant ice. See the latest Key Messages linked at the end
of the discussion.=20

Current radar/sat composite is pretty revealing this afternoon with
the development of a significant swath of precip developing in-of
the Central Plains into the adjacent Lower to Mid-Mississippi
Valley. Shortwave trough ejecting out of the Central Rockies will
continue downstream with general mid-level ascent pattern maximized
within the corridor extending from southeast KS to points east
within Southern MO/Northern AR with a heavy snow footprint
forecast to align within the above corridor. WPC prob snowbands at
the 12z update was still pretty aggressive for a several hr time
frame of 1-2"/hr rates embedded within the primary precip shield=20
moving across the Ozarks until about the three-river confluence at=20
the MO/TN/AR border. Heavy snows over the span of several hours=20
will produce total accumulations generally >8" across that same=20
expanse from KS through northern AR and southern MO through=20
Wednesday morning. High probs (50-80%) for >4" exists just for the=20
00-12z Wednesday period across southern MO, northern AR, and far=20 southwestern KY with lower probs (25-50%) extending further east=20
through the Ohio Valley for the remainder of the period.=20

Further south into Central AR down through northern LA, dominant=20
ptype will continue to trend more favorable for IP/ZR as a shallow=20
warm layer is progged due to the meridional push of Gulf air=20
advecting over top the shallow cold air mass being pushed south on
the southern flank of the Arctic high drilling south over the=20
course of today and tomorrow. Thankfully the ascent pattern is=20
strongest further north, so ice accums are not anticipated to be=20
severe, but still relatively impactful with probs of ice >0.1"=20
holding between 10-30% across the AR/LA border over the course of=20
the forecast period. Ice probs decrease downstream for D2, but=20
still maintain some low probs for between 0.01-0.1" ice accums=20
across northern MS/AL/GA for mainly the 06-14z time frame on=20
Wednesday before precip moves out of the area the second half of=20
the D2 period.=20

By early Wednesday morning, increased jet dynamics over the
Southeast and Mid-Atlantic will aid in generating a surface low
along the Central Gulf coast, propagating east-northeast over the=20
course of Wednesday with a surface low located off the NC coast by
early Thursday morning. The primary disturbance to the west will
still motion across the Ohio Valley into the mountains of the
central and southern Mid-Atlantic leading to moderate snow
accumulations on D2 across eastern KY/southern WV/southwestern VA
leading to probs around 30-50% for at least 4" of snowfall in those
locales during the 12z Wednesday to 12z Thursday period falling
in-between both D1 and D2. Further east into the coastal southern
Mid-Atlantic, our aforementioned surface cyclone over the Gulf into
the Western Atlantic will lead to the greatest QPF footprint for
the D2 period with heavy synoptic based precipitation over places
like the Tidewater of VA down into northeastern NC, mainly in the
form of snow. Moderate precip focus will align within the NC=20
Piedmont across into southeastern NC with a mixed ptype regime
likely to cause some formidable ice accums in the form of sleet
(IP) and freezing rain (ZR). The area across the VA Tidewater will
be the epicenter for the most significant snowfall forecast with
totals between 6-12" expected for areas like Norfolk up through the
U13 corridor between VA Beach/Chincoteague, well-documented with
the latest >4" probs a solid 80+% within that entire zone and >8"
probs up into the 40-60% range. Modest probs for >4" also extend
south into northeastern NC with a decent area of 40-70% probs
existing from Elizabeth City and points northwest.=20

Freezing rain prospects exist across a good portion of eastern NC
and the northern Piedmont of SC with the heaviest totals likely to
fall over areas along and east of I-95. WPC probabilities between
50-80% are forecast for >0.1" ice accretion across portions of
eastern NC with low probs (10-30%) for the northern most portion of
the SC Piedmont. 10-30% probs also exist for as much as 0.25" of
ice accretion over eastern NC as well, although the deterrent for
the threat is the heaviest precip falling within marginally cold
enough air at the surface (30-32F) with periods of heavier precip
falling during the day time which historically curbs ice accretion
rates, especially at these latitudes.=20

Kleebauer


...Great Lakes...=20
Days 1-3...

Cyclonic flow over southern Canada and the Great Lakes on the=20
western side of the elongated upper trough axis will favor a=20
continuation of the lake effect snow for the next couple of days.=20
With 850 temperatures in the -20sC and NW to WNW flow, multi-bands=20
will form off the Upper Lakes with a strong single band off Lake=20
Ontario with an impressive multi-lake moisture feed. The pattern=20
will be slow to unwind, but by early Wednesday a closed low will=20
begin to form over the Corn Belt which will help disrupt the=20
pattern enough to diminish the heavy lake effect snow, but then=20
those height falls will bring in a general/light snow to the region
on Thursday and Friday. WPC probabilities for at least 8 inches of
snow only exist on Day 1 (Wednesday) parts of the Michigan U.P.=20
and off southern Lake Ontario. For central NY between ROC- FZY-=20
SYR, the strong single band will steal the show and continue to=20
dump snow at 1-3"/hr rates with significant accumulation in a=20
narrow swath -- perhaps more than 12 inches of additional snow=20
(10-20% probs). By days 2 and 3, snowfall will be light with most=20
areas seeing less than 4 inches of snow. The greatest potential for
additional snowfall over 4 inches (20-50%) is forecast off Lake=20
Michigan into western L.P. and far northern Indiana on Thursday,
positioned along the eastern and northern periphery of the upper
low.


...Pacific Northwest through the Central Rockies...
Days 1-3...

Initially for tonight, additional height falls out of Canada will=20
drop through central MT with some light snow to the central ID=20
ranges, southwestern MT, and the western WY ranges where WPC=20
probabilities for an additional 6 inches of snow are low (<40%) to
the north but high (>70%) over southern WY and the high peaks of=20
the northern CO Rockies.=20

By early Wednesday, a potent but progressive Pacific system will=20
start to move into the Northwest, spanning the latitudes from=20
NorCal up to the Canadian border. IVT will be modestly high (~90th=20 percentile) into NorCal/southern OR/northern NV toward Idaho,=20
supporting light to moderate snows for the terrain with snow levels
near 3000ft to the north and 5000ft to the south that will rise a=20
bit as the core of the moisture plume pushes through. The system=20
will move steadily along and clear the coast with QPF starting=20
early Thursday, pushing into northern UT/southern ID and into the=20
Rockies. However, moisture will wane and snow will become lighter=20
overall into the end of D2 with the snow confined mainly to the=20
Unitas and higher CO Rockies by then. For the 3-day period, WPC=20 probabilities for at least 8 inches of snow are highest (>70%) over
the higher terrain above 6000ft closer to the coast, 7000-8000ft=20
over the Great Basin, and 9000ft over CO/WY. The next system begins
to enter the Northwest by the end of D3 with lighter snow entering
the northern Cascades.


...Southeastern Mass...
Day 2-3...

The exiting system from the Southeast/southern Mid-Atlantic will=20
track northeastward, and may clip southeastern MA/Cape Cod on
Thursday on its way into Atlantic Canada. The question revolves=20
around the speed of the incoming northern stream upper low and how=20
much it can capture the exiting system and pump up the downstream
ridge. Recent 12z guidance has nudged northward, which is common in
the short range with developing low pressure systems off the coast
as CAMs incorporate latent heat release and stronger WAA in
relation to convection in the warm sector of the system. However,
the best chances for snowfall over 4 inches remains over Nantucket
(70-80%) as well as both Martha's Vineyard and Cape Cod (40-60%),
with low probs (10-20%) clipping far eastern Long Island, southern
CT and the remainder of southeast MA.


Fracasso/Snell



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!5mPmuoW5LsnP4ytmASZ9XcFvE4QBoZOAMQWVvp_1zHOla= XspwSo7cpI_J7s1J04ovX_4L1NURYZIDHud1WBb0slpltc$=20

$$

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FOUS11 KWBC 190701
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 AM EST Wed Feb 19 2025

Valid 12Z Wed Feb 19 2025 - 12Z Sat Feb 22 2025


...Southern Mid-Atlantic States...=20
Day 1...

A significant winter storm will continue to spread eastward into=20
the southern Mid-Atlantic with potentially major impacts including=20
heavy snow and significant ice. See the latest Key Messages linked=20
at the end of the discussion.=20

Surface low along the Central Gulf coast will cross North Florida=20
early this afternoon and parallel the Southeast Coast tonight. The=20
northern stream shortwave responsible for the heavy snow in the=20
Plains will continue eastward into the southern Mid-Atlantic,=20
helping to spread generally light snow to the southern=20
Appalachians, aided by some orographic enhancement. WPC=20
probabilities for at least 4 inches are generally <30%.

As the Gulf low transitions to a western Atlantic/coastal low,=20
precipitation will progress to the VA/NC coast with snow to the=20
north (solidly cold column over VA) and freezing rain and sleet to=20
the south where warmer air aloft will overrun the cold surface=20
temperatures near and just below freezing over eastern NC and into=20
portions of eastern SC as well. Snowfall to the north will likely=20
maximize later this afternoon and evening as the surface low starts
to deepen over the Gulf Stream, with locally heavier rates >1"/hr=20
over southeastern VA, leading to moderate/heavy amounts. WPC=20
probabilities for at least 6 inches of snow are >50% there. There=20
is a much larger footprint of >2" probabilities of at least 40%,=20
extending from southwestern VA eastward, as far north as=20
Fredericksburg, VA to Rehoboth Beach, DE, and as far south as the=20 Raleigh-Durham metro.=20

Into NC, several hours of freezing rain are likely starting this=20
afternoon and continuing into the evening. Accretion will depend on
rainfall rates (which limit accretion), wind, and time of day, but
most of the guidance still indicates the potential for a couple=20
tenths of an inch of ice, roughly along and east of I-95 in eastern
NC. WPC probabilities for at least 0.10" ice are >40% with some=20
areas likely seeing >0.25" ice. Precipitation will wind down=20
overnight and end by Thursday morning.


...Great Lakes/Northeast...=20
Days 1-2...

Lake effect snow will diminish this morning as height falls over=20
the Corn Belt move into the region, favoring widespread light snow=20
over the Great Lakes and Midwest tonight into Thursday. WPC=20
probabilities for at least 4 inches of snow are low (<40%) except=20
for some lingering lake bands and/or lake enhanced snows.


...Pacific Northwest through the Central Rockies...
Days 1-3...

A potent but progressive Pacific system will start to move into=20
the Northwest this morning, spanning the latitudes from NorCal up=20
to the Canadian border. IVT will be modestly high (~90th=20
percentile) into NorCal/southern OR/northern NV toward Idaho,=20
supporting light to moderate snows for the terrain with snow levels
near 3000ft to the north and 5000ft to the south that will rise a=20
bit as the core of the moisture plume pushes through. The system=20
will move steadily along which will end QPF from west to east=20
starting as early as tonight over the Cascades and on Thursday over
the Great Basin. Moisture will wane with decreasing synoptic=20
support into Thursday, with snow confined mainly to the Unitas and=20
higher CO Rockies by then. For the 2-day period, WPC probabilities=20
for at least 8 inches of snow are highest (>70%) over the higher=20
terrain above 6000ft closer to the coast, 7000-8000ft over the=20
Great Basin, and 9000ft over CO/WY. A new system will to enter the=20
Northwest by D3 with lighter snow into the northern Cascades.


...Southeastern Mass...
Day 2...

The exiting system from the Southeast/southern Mid-Atlantic will=20
track northeastward and may clip southeastern MA/Cape Cod on=20
Thursday on its way into Atlantic Canada. The question revolves=20
around the speed of the incoming northern stream upper low and how=20
much it can capture the exiting system and pump up the downstream=20
ridge. 00Z guidance still shows at least some snow into the region,
but vary on how much. The best chances for snowfall over 4 inches=20
remains over Nantucket (~70%) as well as both Martha's Vineyard and
Cape Cod (40-60%), with low probs (10-20%) from Block Island to=20
New Bedford to Plymouth.


Fracasso


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!9sVcZe4TlHpniV6jCGyvBRat6RhwKKhfV5vDeJcEpZbHI= 3DIxoXOdFgeWi1xsDCLbhLvxvOujjMZE38LNF3kw8MjcUs$=20

$$

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FOUS11 KWBC 192113
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 PM EST Wed Feb 19 2025

Valid 00Z Thu Feb 20 2025 - 00Z Sun Feb 23 2025


...Mid-Atlantic and Carolinas...=20
Day 1...

Major winter storm continues into tonight for southern Mid-
Atlantic with heavy snow and notable icing. See the latest Key=20
Messages linked at the bottom.=20

Developing surface low ahead of southern stream wave is off SC/GA=20
border this afternoon. This coastal low strengthens as it shifts=20
northeast off Cape Hatteras through tonight. Heavy snow bands will
persist over southeast VA into northeast NC through this evening
where Day 1 snow probs for an additional >4" after 00Z are 40-70%.
Snow bands shift offshore after midnight. A wintry mix of mainly=20
freezing rain will persist over southern and eastern NC through=20
this evening. Day 1 ice probs for an additional >0.1" after 00Z are
40-70% over portions of the MHX and ILM CWAs.

The northern stream upper low is currently over Iowa and will=20
track to Ohio through tonight before pushing over the northern Mid-
Atlantic Thursday. Generally light snow is expected from this=20
upper low over the Ohio Valley tonight and over the central/=20
southern Appalachians into the DC metro area Thursday morning. Day
1 snow probs for >2" are 40-70% over the WV Highlands and the Great
Smokies.


...Great Lakes/Massachusetts Cape and Islands...=20
Days 1-2...

Lake effect snow reinvigorates over Lake Michigan tonight into
Thursday on the back side of the aforementioned upper low. NNWly
flow brings single band LES to far southwest MI into northern IN
through Thursday where Day 1 snow probs for >4" are 40-60%. NWly
flow late Thursday brings lake enhanced snow downwind of Erie
despite the lake being nearly frozen over. However, fetch from Lake
Huron will aid snowfall. Day 1.5 snow probs for >4" are around 20%
near Erie, PA.

The system developing off the Mid-Atlantic coast Thursday tracks up
off Nova Scotia Thursday night. This will bring the precip shield
with bay/ocean enhanced snow to southeastern MA/Cape Cod and
Islands Thursday afternoon/evening. Day 1.5 snow probs for >4" are
40-70% for the Cape and Islands.


...Pacific Northwest through the Central Rockies...
Days 1-3...

A potent but progressive Pacific system over the PacNW coast early
this afternoon will dig south as it moves inland with the base of
the trough reaching CO by late Thursday. Snow levels drop to 3000ft
over the WA Cascades through this evening before precip cuts off
with Day 1 snow probs for >4" 40-80% at and above pass level.=20

Snow levels over the northern Rockies are around 4000ft and closer
to 6000ft over CO through Thursday as this trough approaches.
Moderate elevation snow can be expected with Day 1 snow probs for

6" 40-80% around the Bitterroots on the ID/MT border,

northeastern NV ranges, the Wasatch, Uinta and Tetons. Snow=20
continues over the CO Rockies through Thursday night with Day 2
snow probs for >6" 30-60% across central and northern CO ranges.=20

The next wave pushes into the Queen Charlotte Sound Friday evening
with another atmospheric river pushing across WA Friday afternoon,
expanding south through OR Sunday. Snow levels at onset are around
4500ft in the WA Cascades Friday, increasing to 5000ft Friday=20
night and 6000ft over WA (and 8000ft over OR) on Saturday. Day 3=20
snow probs for >6" are 30-40% over the only higher WA Cascades with=20
the very high snow levels over OR precluding snow probs for the
isolated higher Cascade peeks at this time.


Jackson



...Winter Storm Key Messages are in effect and linked...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!7p_seGd11bEmj7cMHpvlL3_O0eakYUdrJUNQ2hZcx0xUM= E5s86ssTwHh9rDSkn4s-uaYBrvouwtuxQoVeOll3LvOpCI$=20

$$

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FOUS11 KWBC 200622
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
122 AM EST Thu Feb 20 2025

Valid 12Z Thu Feb 20 2025 - 12Z Sun Feb 23 2025


...Central Appalachians to New England...
Day 1...

A major winter storm which brought significant snow to the
Tidewater area of Virginia and surrounding portions of VA/NC will
continue to eject to the E/NE today while deepening. Snow will end
quickly this morning over VA, but as the low deepens and tracks
well southeast of the 40N/70W benchmark, snow will overspread
portions of coastal southern New England, especially Cape Cod and
the Islands. The system is progressive, but moisture spreading
north ahead of it will maintain periods of snow in far southeastern
MA, with some additional ocean enhanced snowfall likely across the
Cape Thursday night. Total additional snowfall is expected to be
modest, but may exceed 4" especially across the Outer Cape and
Nantucket as reflected by WPC probabilities of 30-50%.

Behind this potent surface low, an anomalous upper low will race
from the Ohio Valley to off the Mid-Atlantic coast by this evening,
bringing an arc of 500mb heights below the 2.5th climatological
percentile according to NAEFS. Steep lapse rates beneath this upper
low combined with moistening of the low-to-mid levels of the
column will result in a pivoting axis of moderate snowfall, which
may accumulate significantly in the higher terrain of WV where WPC probabilities for 4+ inches are locally 50-70%. Farther east,=20
moderate snow rates may bring some light accumulations from near=20
Greensboro, NC northeast through Hartford, CT. Although=20
accumulations will be less than 1 inch in most places, this snow=20
falling atop very cold ground could cause hazardous travel.


...Great Lakes...
Day 1...

Lake effect snow (LES) will develop in the wake of the potent upper
low moving through the Ohio Valley and into the Mid-Atlantic today.
NW flow and accompanying CAA will produce a favorable environment
across the lakes, most notably SE of Lake Michigan early D1, and
then shifting to downstream (SE) of Lakes Erie and Ontario tonight
into Friday morning. The flow is not ideal along the long fetch of
the lakes except Lake Michigan, and duration is likely to be
relatively short, but WPC probabilities for 4+ inches of snow reach
as high as 30-50% across far SW MI near the lakeshore of Lake
Michigan, as well as along the Chautauqua Ridge east of Lake Erie.



...Central Rockies...=20
Day 1...

A weakening shortwave moving out of the Great Basin will dig E/SE
into the Central Rockies Thursday, combining with a weak jet streak
aloft to produce widespread deep layer ascent to support wintry
precipitation from Idaho through Colorado. A surface low beneath
the shortwave will traverse across Utah and Colorado, providing
additional ascent, and although moisture is near normal according
to NAEFS PW anomalies, this will result in a swath of moderate to
heavy snow, especially in the higher terrain of the Wasatch,
Uintas, and CO Rockies, primarily above 4000 ft. The waning=20
amplitude of this upper trough will allow precip to wane towards=20
the end of D1, but WPC probabilities for 6+ inches of snow are high

70%) along the Wasatch, higher terrain of the Uintas, and into

portions of the CO Rockies.


...Pacific Northwest...
Days 2-3...

A deepening trough well off the Pacific Coast will begin to advect
moisture onshore the Pacific Northwest beginning Friday night. This
moisture plume will be characterized by IVT within an atmospheric
river (AR) which has a high probabilities (>70%) of exceeding 500
kg/m/s according to both the GEFS and ECENS. Additionally, this
AR will have significant duration as probabilities for 500 IVT
exceeding 50% persist for around 48 hours from Friday night through
just beyond the end of this forecast period. The overlap of this
robust IVT and accompanying WAA with intensifying jet level
diffluence and mid-level divergence will result in expanding
precipitation, likely occurring in two distinct waves: one Friday
night into Saturday morning, and another Saturday night through
Sunday.=20

Within the first wave, snow levels will rise gradually to 4000-6000
ft along and west of the Cascades, but cold air remaining
entrenched to the east will keep snow levels below 3000 ft across
portions of interior OR and WA. With the second surge, however,
stronger WAA will lift snow levels to 6000-8000 ft, generally
keeping significant snow accumulations above pass levels. On D2,
WPC probabilities for 4+ inches that are above 50% are confined to
the highest terrain of the WA Cascades, although Washington Pass
may receive a few inches of snowfall D2. During D3, WPC
probabilities for 4+ inches increase in the WA Cascades, but again
at only the higher elevations, while additionally spreading east
into the Northern Rockies.



Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-YC_Rzo2-WTs32sNk5n8Uk_LEXPHuF_vLsQR2QfQ2V1f-= wQVDZjlj7ng55ZUCqc-mv48rLqVnSf_OoIqT3TfpyjPdvk$=20

$$

=3D =3D =3D
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FOUS11 KWBC 202027
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EST Thu Feb 20 2025

Valid 00Z Fri Feb 21 2025 - 00Z Mon Feb 24 2025


...Colorado Rockies and Central High Plains...=20
Day 1...

Shortwave trough axis over Utah this afternoon will shift east over
CO tonight and into western KS Friday morning. Weak jet streak=20
aloft and PVA from the trough will produce widespread deep layer=20
ascent to support snow over CO tonight with banding extending east
over the Palmer Divide, through eastern CO and into western KS late
tonight into Friday. Day 1 snow probs for >6" after 00Z are 40-80%
in the I-70 corridor of north-central CO Terrain and around 30% on
the I-25 corridor over the Palmer Divide near Castle Rock.
Probabilities for >2" spread east along I-70 to Limon, but given
the banding potential from upper forcing, there is potential for
over an inch into KS.=20


...Pacific Northwest to the Northern Rockies...=20
Days 2-3...

Mid-level low pressure pushes across the Queen Charlotte Sound
Friday evening with moisture advection and relatively short-lived=20
moderate precip to the south over the Pacific Northwest Friday=20
night. A broader trough approaches the Pacific Northwest this
weekend with heavier precip then expected Saturday afternoon
through Sunday.=20
For Friday night expect snow levels to gradually rise to 5000 ft=20
along the west side of the WA Cascades with cold air entrenched on
the east side keeping snow levels around 2000ft. Day 2 snow probs=20
for >6" are 50-80% for only the higher WA Cascades and far northern
ID terrain.


The broader moisture surge Saturday afternoon brings widespread
6000-8000 ft snow levels, keeping significant snow accumulations=20
above Cascades pass levels, with 6000ft snow levels inland over the
northern Rockies. Day 3 snow probs for >6" are 40-80% on the higher
WA Cascades, western Sawtooths, ranges around Glacier NP, and the
Tetons. Moderate precip will continue over terrain into Sunday
night.


Jackson




...Cold Key Messages are in effect for much of the southern U.S. as
linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!5ROePMOUawYh1Xj1cMQMIqeJ98h-81saYOQHqDbWQYjou= dqHOFkqgbcrz3CTnxnk4zLaxO9YIIgnhhn6VjNcX7Ke1R8$=20

$$

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FOUS11 KWBC 210623
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
123 AM EST Fri Feb 21 2025

Valid 12Z Fri Feb 21 2025 - 12Z Mon Feb 24 2025


...Pacific Northwest to the Northern Rockies...=20
Days 1-3...

An increasingly active pattern across the Pacific and into the
Northwest CONUS will drive two rounds of wintry precipitation
across the region through the weekend.

The first of these will approach this evening as a modest shortwave
impulse sheds from a larger closed low over the Pacific and moves
onshore by 00Z/Saturday. This will push a weakening cold front
onshore from an occluded low filling across British Columbia.
Modestly pinched mid-level flow will help surge moisture into the
region ahead of this front, characterized by PWs above the 90th
climatological percentile across WA according to NAEFS. The
accompanying ascent through WAA and then convergence along the
front itself will help expand precipitation across the region, but
with snow levels rising to 5000 ft west of the Cascades, and rising much
more slowly to the east. This will keep snow accumulations=20
generally above pass level (Washington Pass the exception), with=20
light icing possible across eastern WA state/the Columbia Basin.=20
Duration and intensity of precipitation D1 into D2 is likely to be
limited, so WPC probabilities for more than 4 inches of snow above
50% are confined to just the highest peaks of the WA Cascades.

After a brief break in precipitation Saturday, a more substantial
plume of moisture pivots onshore beginning Saturday evening/night,
driven by an atmospheric river (AR) which has high probabilities

90%) in both the ECENS and GEFS for IVT to exceed 500 kg/m/s.

This plume will be advected eastward thanks to increasingly
confluent flow just west of the coast and downstream of a
sharpening closed low, aided by a strengthening upper level jet
streak. By 00Z Sunday, IVT according to NAEFS will exceed the 99.5
percentile within the CFSR database, and this will continue to
spread across WA, northern ID, and into MT/WY by the end of the=20
forecast period. This impressive moisture combined with strong=20
synoptic ascent will result in an expansion of heavy precipitation,
but with snow levels concurrently rising to 6000-8000 ft. This=20
indicates that despite precipitation being very heavy at times,=20
most of the snow will be confined to the highest elevations and=20
well above pass levels. This is reflected by WPC probabilities D2=20
that are 70% or more for 6+ inches in the higher WA Cascades, which=20
then expand eastward, reaching 70% or more for 6+ inches across=20
portions of the Sawtooth, Northern Rockies, and Grand Tetons D3.


Weiss


...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!7iftjcGbJrqAmFrnSmucZ6olkRGypWtc5hu11AASOZYzz= wxmh1cjHTXHb8PVQNqvJwsdcBMgkPHm7e6lKPV_xWjo1HQ$=20

$$

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FOUS11 KWBC 220711
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
211 AM EST Sat Feb 22 2025

Valid 12Z Sat Feb 22 2025 - 12Z Tue Feb 25 2025



...Pacific Northwest through the Northern Rockies...
Days 1-3...

A closed mid-level low tracking slowly south of the Aleutians will
shed lobes of vorticity eastward and onshore the Pacific Coast,
spreading precipitation from the Pacific Northwest through the
Northern Rockies into early next week.

Generally W to SW flow will persist across the Pacific during this
time, with enhanced confluence south of the Aleutian Low enhancing
moisture advection and IVT as an atmospheric river (AR). Both ECENS
and GEFS probabilities indicate that IVT will almost certainly

90%) exceed 500 kg/m/s, with potentially 3 consecutive days of

IVT exceeding 250 kg/m/s surging onshore beginning this evening.
Within this moisture plume, PWs are progged by NAEFS to exceed the
99.5 percentile of the CFSR database, especially late D1 through
the end of D2 from the WA/OR coasts to as far inland as the Central
Rockies. Shortwaves/vorticity spokes rotating within this flow will
cause periodic enhancement to ascent leading to heavier and more
widespread precipitation. Although the timing of these features is
not fully agreed upon by the guidance, consensus suggests bouts of
heavier precipitation are likely beginning late D1 and again late
D2. While this will result in heavy snow in higher terrain features
across the region through the period, snow levels will climb
steadily within the AR/accompanying WAA. Snow levels begin the
period around 4000-6000 ft, then climb to as high as 7000-9000 ft,
especially during D2. This will keep most significant snow
accumulations above area pass levels.

Although waves of heavy snow are likely in the higher terrain each
day, the heaviest accumulations are forecast on D2 when WPC
probabilities support a high risk (>70%) for more than 6 inches of
snow across the higher WA Cascades, the Northern Rockies near
Glacier NP, the Sawtooth, and near the Grand Tetons/Yellowstone NP.
During D3, the highest probabilities shift back into the WA/OR
Cascades with slightly lower snow levels supporting high
probabilities (>70%) for more than 6 inches, and 3-day snowfall in
the Cascades could be measured in several feet above 5000 ft
elevation. Additionally, some light icing is expected in the
Columbia Basin and parts of eastern OR where WPC probabilities D2
reach 10-30% for up to 0.1" of ice.

Weiss




$$

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FOUS11 KWBC 220710
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
210 AM EST Sat Feb 22 2025

Valid 12Z Sat Feb 22 2025 - 12Z Tue Feb 25 2025



...Pacific Northwest through Northern Rockies...
Days 1-3...

A closed mid-level low tracking slowly south of the Aleutians will
shed lobes of vorticity eastward and onshore the Pacific Coast,
spreading precipitation from the Pacific Northwest through the
Northern Rockies into early next week.

Generally W to SW flow will persist across the Pacific during this
time, with enhanced confluence south of the Aleutian Low enhancing
moisture advection and IVT as an atmospheric river (AR). Both ECENS
and GEFS probabilities indicate that IVT will almost certainly

90%) exceed 500 kg/m/s, with potentially 3 consecutive days of

IVT exceeding 250 kg/m/s surging onshore beginning this evening.
Within this moisture plume, PWs are progged by NAEFS to exceed the
99.5 percentile of the CFSR database, especially late D1 through
the end of D2 from the WA/OR coasts to as far inland as the Central
Rockies. Shortwaves/vorticity spokes rotating within this flow will
cause periodic enhancement to ascent leading to heavier and more
widespread precipitation. Although the timing of these features is
not fully agreed upon by the guidance, consensus suggests bouts of
heavier precipitation are likely beginning late D1 and again late
D2. While this will result in heavy snow in higher terrain features
across the region through the period, snow levels will climb
steadily within the AR/accompanying WAA. Snow levels begin the
period around 4000-6000 ft, then climb to as high as 7000-9000 ft,
especially during D2. This will keep most significant snow
accumulations above area pass levels.

Although waves of heavy snow are likely in the higher terrain each
day, the heaviest accumulations are forecast on D2 when WPC
probabilities support a high risk (>70%) for more than 6 inches of
snow across the higher WA Cascades, the Northern Rockies near
Glacier NP, the Sawtooth, and near the Grand Tetons/Yellowstone NP.
During D3, the highest probabilities shift back into the WA/OR
Cascades with slightly lower snow levels supporting high
probabilities (>70%) for more than 6 inches, and 3-day snowfall in
the Cascades could be measured in several feet above 5000 ft
elevation. Additionally, some light icing is expected in the
Columbia Basin and parts of eastern OR where WPC probabilities D2
reach 10-30% for up t0 0.1" of ice.

Weiss

$$

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FOUS11 KWBC 212029
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EST Fri Feb 21 2025

Valid 00Z Sat Feb 22 2025 - 00Z Tue Feb 25 2025


...South-Central Texas...
Day 1...

Low level NEly flow from high pressure centered over Arkansas will
persist over the eastern half of Texas through Saturday morning.
Dry/cold air advection in this flow will continue to be overrun by southerly/Gulf-moisture laden air with an expansion of precip from
South to Central Texas tonight. There is question to how far sub-
freezing temps make it tonight, but as of now there is sufficient
confidence in freezing rain accumulating over central Texas, around
and a bit east of the San Antonio metro area (where WFO EWX has an
advisory). There is potential for some elevated ice glaze farther
south into the CRP CWA, but that fine line is not that clear as of
this time. Day 1 ice probabilities for >0.01" are 40-60% in and
east of San Antonio with 10% probs extending from the Austin metro
to Laredo.


...Pacific Northwest through Northern Rockies...
Days 1-3...

Pacific moisture advects over the PacNW to the northern Rockies
through Monday with a few upper trough passages expected. Higher
elevation snow is expected through the next three days with the
heaviest precip Saturday afternoon through Sunday when there are
rather high snow levels.

An upper low moves over the Queen Charlotte Sound through this
evening. 0.75" PW air flows across WA through Saturday morning with
snow levels west of the Cascades crest generally rising from 4500ft
to 5500ft while persisting around 3000ft east of the crest over the
northern Columbia Basin due to entrenched cold air. Day 1 snow
probs for >6" are 40-70% in the north WA Cascades and the Selkirks
in far north Idaho.

The next wave in this zonal flow arrives to Vancouver Island
Saturday midday with a plume of 1 to 1.25" PW air streaming over
WA/OR Saturday afternoon through Sunday. Snow levels rapidly rise
to 8000ft in this plume for Saturday night, though snow levels drop
to around 6000ft in the north WA Cascades Sunday afternoon under
the next shortwave trough axis. This moisture also spreads across
the northern Rockies where snow levels will be 5000-6000ft. Day 2
snow probs for >6" are 40-70% in the north WA Cascades, western
Sawtooths, Bitterroots, and ranges around Glacier NP. THe pattern
for the Day 3 snow probs for >6" are similar to Day 2 just with
lower probs for the Sawtooths and Bitterroots with an expansion
over the southern Absarokas and Tetons (40-70% there). Three day
snow totals over 3ft are possible in the highest WA Cascades with
more like 1-2ft in the higher Sawtooths, Tetons, and Lewis Range at
Glacier NP.

This is nearly all above mountain road passes and is generally a
beneficial precip event for watersheds in the NW.


Jackson



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FOUS11 KWBC 221908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
208 PM EST Sat Feb 22 2025

Valid 00Z Sun Feb 23 2025 - 00Z Wed Feb 26 2025

...Pacific Northwest through the Northern Rockies...
Days 1-3...

The overall synoptic evolution forecast remains pretty consistent
among guidance as of the 12z NWP suite. A closed mid- level low
tracking slowly south of the Aleutians will continue shedding
lobes of vorticity eastward and onshore the Pacific Coast,
spreading precipitation from the Pacific Northwest through the
Northern Rockies into early next week.

Generally W to SW flow will persist across the Pacific during this
time, with enhanced confluence south of the Aleutian Low enhancing
moisture advection and IVT as an atmospheric river (AR). Both ECENS
and GEFS probabilities indicate that IVT will almost certainly

90%) exceed 500 kg/m/s, with 3 consecutive days of IVT exceeding

250 kg/m/s surging onshore beginning this evening. Within this
moisture plume, PWs are progged by NAEFS to exceed the 99.5
percentile of the CFSR database, especially late D1 through the end
of D2 from the WA/OR coasts to as far inland as the Central
Rockies. Shortwaves/vorticity spokes rotating within this flow will
cause periodic enhancement to ascent leading to heavier and more
widespread precipitation. Although the timing of these features is
not fully agreed upon by the guidance, consensus suggests bouts of
heavier precipitation are likely beginning late D1 and again late
D2. While this will result in heavy snow in higher terrain features
across the region through the period, snow levels will climb
steadily within the AR/accompanying WAA. Snow levels begin the
period around 4000-6000 ft, then climb to as high as 7000-9000 ft,
especially during D2. This will keep most significant snow
accumulations above area pass levels.

As me move into D3, a tertiary shortwave trough will pivot
underneath the prominent gyre to the north generating a more
significant height fall pattern as we step into Tuesday morning.
Snow levels that rose considerably in the periods prior will see
them decrease rapidly as the advancing shortwave trough allows for
colder temps to seep down into the previous 4000-6000 ft range
culminating in more widespread heavy snowfall across the Northern
Cascades and higher elevations of the Olympics in WA. Steady
progression of colder air mixing further into the column will
protrude areas east of the coastal ranges with areas inland
towards northern ID and northwestern MT seeing an uptick in
snowfall for the 12-00z time frame Tuesday into Wednesday. Heaviest
snow will still be confined to the Cascades, but some areas east
of the mountain chain will see >4" of snowfall, namely over the
Bitterroot Range extending northeast towards the Cabinet Mtns., and
southeast into the Absaroka Range.

The heavy snow footprint continues to be most prominent in that D2
to D3 time frame with the highest probs (>70%) for >4" located over
the ranges above. Additional high probs over 70% will exist in the
highest elevations of the Olympics by D3 due to the incoming
disturbance. Totals >8" are split between the remainder of D1 with
a break between D1 and part of D2, but will pick up significantly
in both magnitude (50-80%) and spatial coverage of the higher probs
across the PAC Northwest by the end of D2 into D3 within the
vicinity of the Cascades, Olympics, and Bitterroot Ranges. This
will culminate in the highest elevations encountering several (4+)
feet of snow over the next 72 hrs. with 1-3 feet forecast for areas
between 4000-7000 ft MSL. Additionally, some light icing is
expected in the Columbia Basin, as well as parts of eastern OR
where WPC probabilities D1 into early D2 reach 10-30% for up to
0.1" of ice.

Weiss/Kleebauer

...Tug Hill through Northern Green & White Mountains...
Day 1-2...

Shortwave trough analyzed over the northern Great Lakes will
continue pushing downstream into neighboring Quebec with the
southern fringes of the energy bisecting Upstate NY through
Northern New England by this evening. Sufficient low-level
buoyancy generated by modest delta-T's over Lake Ontario will
create a moderately strong singular band that will align downwind
of the lake with the fetch aimed into the Central and Southern Tug
Hill Plateau. Combined moisture fetch and local upslope component
will allow for a targeted area of heavy snow to those areas within
the band placement. High probs of 70-90% for >4" exist within the
window of 00-18z Sunday with a very small area of 40-70% probs for

6" intersecting the Tug Hill area between Watertown to Pulaski and

points inland. This is the primary zone for heavy snow within the
Northeastern U.S, but some upslope snows within the Northern Green
and White Mountains of VT/NH also point to some modest
probabilities of >4", especially as you enter the Greens from Mount
Mansfield and points north.

Kleebauer

$$

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FOUS11 KWBC 230738
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
238 AM EST Sun Feb 23 2025

Valid 12Z Sun Feb 23 2025 - 12Z Wed Feb 26 2025

...Pacific Northwest through the Northern Rockies...
Days 1-3...

Long duration atmospheric river (AR) begins before the forecast
period, and continues through Tuesday. This AR is driven by
confluent mid-level flow overlapped by multiple impressive Pacific
jet streaks, resulting in pronounced onshore flow of moisture. The
accompanying IVT has a high probability (>80% from ECENS and GEFS)
of exceeding 500 kg/m/s through Monday, with a slow wane
thereafter. Within this plume of moisture, forcing for ascent will
be periodically enhanced by shortwave troughs rotating through the
flow as impulses shed from a strong closed mid-level low out over
the Pacific Ocean. Each of these impulses will produce enhanced
ascent to expand and intensify the accompanying precipitation,
leading to rounds of heavy snow from the Cascades through the
Northern Rockies. However, the WAA within the AR will lift snow
levels to as high as 8000 ft, before latitudinal variations develop
on either side of a stalled front.

For D1, a closed 500mb low pushing onshore British Columbia will
pulse a lobe of vorticity into WA state, accompanied favorably by
coupled jet streaks. This will combine with a cold front pushing
eastward to enhance ascent and drive rounds of heavy precipitation
from northern CA through the Northern Rockies, with upslope flow
into terrain features resulting in the heaviest accumulations of
precipitation. Snow levels during this time will rise to generally
6000-8000 ft, keeping snow confined above pass levels. However,
where it does snow, accumulations will be significant as reflected
by WPC probabilities that indicate a high risk (>70%) for 8+ inches
in the Sawtooth, Northern Rockies near Glacier NP, and the Tetons
of WY.

This first front will then become elongated west-east as the
mid-level pattern becomes flattened in response to a sharper trough
approaching from the West. This will allow some colder air to drain
southward but remain confined generally to WA, northern ID, and MT,
with a sharp gradient in snow levels existing along this boundary
(3000 ft north, 6000 ft south). This will be relatively short lived
however, as the stronger trough axis drives a potent closed low and accompanying surface low towards the WA/OR coast late Monday. This
will once again result in enhanced ascent through WAA, PVA, and
upper diffluence, with a second surge in precipitation expanding
east across the area. Snow levels climb again to as high as 6000 ft
in many areas late Monday into early Tuesday, before the associated
cold front drives eastward by the end of the period. While this
will cause snow levels to fall quickly, it will also result in
rapid drying of the column, bringing an end to the heavy
precipitation.

D2 snowfall is likely to be heaviest along the spine of the
Cascades and into the Olympics of WA, where WPC probabilities are
high (>90%) for 8 inches, and locally 1-3 feet is possible in the
highest elevations. During D3 the heaviest precipitation spreads
inland as far as the Northern Rockies and into the vicinity of
Yellowstone NP, but the heaviest accumulations are likely again
across the WA Cascades where WPC probabilities are above 50% for an
additional 8+ inches of snow.


Weiss


$$

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