ACUS01 KWNS 141248
SWODY1
SPC AC 141246

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0746 AM CDT Sun Apr 14 2024

Valid 141300Z - 151200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN OHIO INTO PENNSYLVANIA...

...SUMMARY...
Severe thunderstorms should develop late this afternoon in a narrow
corridor across the upper Ohio Valley into Pennsylvania and
vicinity. Damaging winds should be the main threat. Severe hail and
perhaps a couple of tornadoes also appear possible as this activity
spreads slowly southward into this evening.

...Ohio Valley into the Mid-Atlantic and Northeast...
Early morning surface observations show a dearth of low-level
moisture from the upper OH Valley into the Mid-Atlantic, with
surface dewpoints generally in the 30s. However, boundary-layer
moisture will gradually increase through the day across these
regions, as a weak surface low migrates eastward from the Great
Lakes across NY. By late afternoon, generally upper 40s to low 50s
surface dewpoints should become focused in a narrow corridor along
and south of front from OH into PA and southern NY. With upper
troughing persisting over eastern Canada and parts of the Northeast,
generally westerly mid-level winds across the Midwest/OH Valley will
aid in the eastward advection of an EML and associated steep
mid-level lapse rates. Even though low-level moisture is expected to
remain limited, these steepened lapse rates aloft, along with
diurnal heating, should encourage the development of weak to locally
moderate MLCAPE late this afternoon.

Surface-based thunderstorm initiation across this region will likely
be delayed until 20-21Z or later, as lingering MLCIN and a cap
gradually erodes. Initial development should be focused along the
front across parts of eastern OH into western/central PA, with
additional development eventually occurring into eastern PA and
parts of southern NY. Given strong deep-layer shear and favorable
lapse rates, large hail may occur with the more robust cores
initially. Some threat for a couple of tornadoes may also exist with semi-discrete convection, as sufficient low-level shear will be
present for updraft rotation. But, with the surface front aligned
mostly parallel to the enhanced westerly low/mid-level flow, upscale
growth into small bowing clusters should quickly occur as convection
spreads south-southeastward. Scattered damaging winds will likely
become the main threat with these clusters through the early evening
in a narrow spatial corridor extending from eastern OH into PA where instability and steep low/mid-level lapse rates should be maximized.
The damaging wind threat will gradually decrease through the evening
as instability lessens with southward/eastward extent.

..Gleason/Grams.. 04/14/2024

$$
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ACUS01 KWNS 161244
SWODY1
SPC AC 161242

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0742 AM CDT Tue Apr 16 2024

Valid 161300Z - 171200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF IOWA...NORTHERN MISSOURI...AND NORTHWESTERN ILLINOIS...

...SUMMARY...
Scattered severe thunderstorms appear likely today, centered mostly
over northern Missouri, Iowa, and northwestern Illinois. Large hail,
damaging winds, and tornadoes should occur in this corridor. More
isolated activity could develop as far south as the Ozarks of
northern Arkansas.

...Synopsis...
An upper trough/low over the central Plains this morning will
continue to eject east-northeastward across the mid MO Valley and
Upper Midwest through tonight. A 70-90 kt mid-level jet will
overspread parts of the Midwest through the day, contributing to
substantial deep-layer shear and thunderstorm organization. At the
surface, a 990 mb low over central NE will likewise develop
east-northeastward through the day in tandem with the upper wave. A
warm front should lift northward across parts of the Midwest, with
generally low to mid 60s surface dewpoints present across the warm
sector as far south as the Ozarks. A composite Pacific cold
front/dryline will move quickly eastward from the southern/central
Plains into the mid Ms Valley by this evening. This boundary should
stall across the southern Plains, and may begin to lift northward
late tonight.

...Midwest/Mid Mississippi Valley...
A large area of showers and thunderstorms is ongoing this morning
from parts of eastern KS/NE/SD into IA. Much of this activity across
the central Plains is being driven by large-scale ascent associated
with the ejecting upper trough/low, along with strong warm/moist
advection with a 40-50 kt southerly low-level jet. As this
convection continues to spread eastward this morning in tandem with
the migrating low-level jet axis, it will probably become more
elevated, especially as it moves into northern MO and IA and a less
unstable airmass to the north of the warm front. Still, an isolated
severe threat may persist in the short term with these
thunderstorms. The effect of this early-day convection on robust destabilization in its wake along/ahead of the cold front remains a
concern and potentially limiting factor for additional severe
thunderstorm development this afternoon. Even so, most guidance,
including multiple recent runs of the RAP, shows a narrow corridor
of weak to moderate instability developing along/south of the warm
front in IA, and ahead of the cold front sweeping eastward across
MO/IA. This re-destabilization should be aided by a pocket of steep
mid-level lapse rates and cold temperatures aloft on the southeast
side of the upper trough/low.

Assuming that low to mid 60s surface dewpoints and modest daytime
heating can aid in this instability actually materializing, then a
risk for supercells should exist over parts of IA, northern MO, and northwestern IL. Both low-level and deep-layer shear appear strong
enough for supercells. Steep lapse rates will aid in hail
production, with some chance for 2+ inch diameter stones with the
more robust cores. Tornadoes will also be a concern, as the enhanced boundary-layer flow and enlarged/curved hodographs associated with a
the low-level jet will aid in updraft rotation. The best tornado
potential will probably be focused along/near the warm front in IA,
where the greatest low-level shear is forecast. Here, a strong
tornado appears possible. Isolated to scattered damaging winds may
also occur.

Farther south into the Ozarks and Mid-South, the potential for
severe thunderstorms appears more conditional. Various NAM/RAP
forecast soundings exhibit generally poor lapse rates, with at least
weak inhibition through much of the period. Given these regions
displacement from the upper trough/low to the north, it remains
unclear how robust updrafts will be in a more marginal low/mid-level
lapse rate environment. Still, have maintained the Slight Risk into
parts of the lower MS Valley, but convection may struggle to
intensify this afternoon/evening.

..Gleason/Grams.. 04/16/2024

$$
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ACUS01 KWNS 301250
SWODY1
SPC AC 301248

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Tue Apr 30 2024

Valid 301300Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
AND WESTERN IOWA TO NORTHEASTERN KANSAS...

...SUMMARY...
The greatest threat for severe weather (large hail severe gusts and
a few tornadoes possible) is from western and central Iowa to
northeastern Kansas.

...Synopsis...
A fairly low-amplitude, nearly zonal pattern will remain across the
CONUS east of the Rockies, and downstream from a slow-moving mid/
upper-level cyclone now over the northern Rockies. By the end of
the period, this cyclone (containing numerous mesoscale vorticity lobes/shortwaves) should pivot to the northern High Plains, roughly
astride the northern border of MT and ND with the Canadian Prairie
Provinces.

The most impactful associated feature will be a shortwave trough
evident in moisture-channel imagery over portions of eastern MT into central/southern WY. This perturbation should shift eastward to
near a BIS-MHE-LNK axis by 00Z, then eject northeastward over the
upper Mississippi Valley tonight. Meanwhile, in response to height
falls and synoptic trough amplification over the Intermountain West,
south of the cyclone, flow over the central and southern Rockies and
adjoining Plains should back gradually to southwesterly, but with
few, if any, notable embedded perturbations today.

At the surface, 11Z analysis showed a low over northwestern SD, with occluded/cold front arching across western SD, western NE and
northern CO. The low should move eastward to northeastern SD by
00Z, with a triple point over northern IA or extreme southern MN,
warm front to northern IL, and cold front to northeastern and
south-central KS, the OK Panhandle, and Raton Mesa. That low should
move over southern MN and northern WI through tonight, possibly
reaching western Upper MI by 12Z, while the cold front reaches
northeastern IL, the central/western Ozarks, and northern OK,
stalling near a lee-side/frontal-wave low in the CAO/DHT area by
12Z. As moisture return continues, a dryline will become better
defined today from central KS to the TX Permian Basin, shifting
eastward to east-central KS, north-central/southwestern OK,
northwest TX, and northernmost Coahuila before stalling late this
afternoon.

...Lower Missouri Valley and vicinity...
Widely scattered to scattered thunderstorms are forecast to form
this afternoon--earliest around the Siouxland area and later with
southward extent. All forms of severe are possible, but with an
earlier lean to the greatest hail vs. greatest wind threats.
Activity should coalesce from mid-late afternoon onward and shift
eastward over the outlook area, weakening this evening into tonight.

Observed thermodynamic profiles and forecast soundings from this
area southward toward the Gulf Coast reasonably show a shallow moist
layer in low levels, easily mixed via diurnal heating. This appears legitimate, related to trajectories emanating from an extensive
area of outflow observed over the northwestern Gulf and adjoining
parts of east TX, LA and AR to the lower Mississippi Valley. That
outflow came from MCS activity yesterday. Nonetheless, diurnal
heating should help to steepen low/middle-level lapse rates
considerably and eliminate MLCINH -- by early afternoon over
northwestern parts of the outlook area (where moisture will be lower
but deep-layer lift/cooling aloft greater), and mid/late afternoon
roughly south of I-80 (stronger heating/moisture, adequate lift).

Strengthening and veering of winds with height will yield enlarged
hodographs and favorable deep-shear profiles for supercells, albeit
with somewhat high LCL atop a deep mixed subcloud layer. Forecast
soundings reasonably depict MLCAPE ranging from around 500-1000 J/kg
in the SUX/FSD area to over 3000 J/kg down the narrow plume of
favorable instability in eastern KS. Effective-shear magnitudes of
50-65 kt and SRH of 200-400 J/kg are expected. This parameter space
and profile will support severe wind and hail, both in early
supercell stages (when large to locally very large hail also is
expected), and as upscale aggregation of convection occurs with
small-scale cold pools.

...Southern Plains...
Isolated to locally scattered thunderstorms, including a few
supercells, are possible for a few hours this afternoon into early
evening, initiating near the dryline and moving slowly east-
southeastward (right movers) to faster northeastward (left movers).
Large hail and severe gusts will be the main concerns, and a
conditional significant (2+ inch diameter) hail risk may occur with
any sustained supercell in this corridor. However, in the absence
of large-scale support, specific foci along the dryline appear
unclear, with coverage uncertain (and probably low) over most of the
area. This makes predictability low for any specific mesobeta-scale
patch where greater unconditional probabilities may develop.

Strong surface heating along the dryline will support at least
isolated thunderstorm development mid/late this afternoon, in an
environment of modest low/middle-level flow but strong veering with
height. Before dark, SRH will be small in the lowest couple km,
however, with effective shear magnitudes in the 30-40-kt range,
supporting a blend of organized multicell and transient/isolated
supercell potential. Steep lapse rates, dewpoints commonly in the
60s F, and enough heating for a deep/well-mixed subcloud layer,
should support MLCAPE of 2000-3500 J/kg. Activity should weaken
considerably after dark.

...NY...
Widely scattered thunderstorms are possible today in a zone of
large-scale ascent preceding the trough aloft, superimposed on
modest low-level convergence related to low-level trough drifting
eastward over the area. The trough may manifest at the surface as a
weak low, but projected inflow-layer parcels should remain largely
(if not entirely) elevated above the boundary layer, where moisture
will be greatest and MUCINH weakest. Elevated MUCAPE of 500-1200
J/kg is possible, and briefly surface-based parcels may be
attainable in pockets of sustained heating over portions of the
Finger Lakes to Catskills vicinities. The best-organized cells may
produce small hail and subsevere gusts. Lack of greater near-
surface instability (magnitude and area), and weak midlevel lapse
rates, preclude a severe threat warranting an unconditional outlook
at this time.

..Edwards/Leitman.. 04/30/2024

$$
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