AUS01 KWNH 152046
FFGMPD
FLZ000-ALZ000-MSZ000-LAZ000-160230-

Mesoscale Precipitation Discussion 0065
NWS Weather Prediction Center College Park MD
446 PM EDT Sat Mar 15 2025

Areas affected...Eastern LA...Southeast MS...Southern AL....

Concerning...Heavy rainfall...Flash flooding possible

Valid 152045Z - 160230Z

SUMMARY...Lines of rotating cells are starting to congeal into a
more single line and starting to advance eastward. Better
alignment of moisture and instability axis will retain moisture
flux to support up to 2"/hr rates; however, a more easterly
component may reduce some training and therefore flash flooding
will become more scattered in nature over higher FFG.=20

DISCUSSION...GOES-E WV suite depicts core of negative tilt
shortwave has swung through Arkansas into the middle MS valley,
this has resulted in low level veering and alignment of the
moisture and instability axis across E LA into S MS. Currently,
merging cells across the best confluence in S MS is resulting in
higher than average rainfall rates (to other cells) due to
slightly backed flow downshear of surface low near BTR. Moisture
flux of 20-25kts of low 70s Tds and 2000-2500 J/kg of MLCAPE will
maintain strong updrafts and efficient low level moisture flux
convergence for rates of 2"/hr, perhaps as high as 2.5-3" for very
short periods when isallobaric flow increases with cycling of updrafts/supercells.=20

Upper-level flow is starting to increase with overspreading of WSW
3H jet over 110kts, increasing easterly propagation component to
the convective line. This will reduce training in the longer
period, so supercells will continue to remain efficient along the
line with streets of 2-3" totals possible. Combined with the
generally higher FFG values across S MS/AL and E LA, flash
flooding should become more scattered/isolated in nature as the
line increases forward speed. However, there are numerous prone
urban centers, particularly along I-10 that may be quickly
over-whelmed by 1-2" sub-hourly totals if directly impacted by the
leading broad downdrafts. As such, flash flooding is considered
possible across the area of concern. An additional MPD will be
issued subsequent to discuss higher likelihood flooding conditions
further north.=20=20

Gallina

ATTN...WFO...BMX...JAN...LIX...MOB...

ATTN...RFC...LMRFC...SERFC...NWC...

LAT...LON 33398592 32748566 31788611 31128717 30488834=20
29839028 30519073 31999005 32718931 33318745=20

$$

AWUS01 KWNH 152129
FFGMPD
GAZ000-TNZ000-KYZ000-ALZ000-MSZ000-160315-

Mesoscale Precipitation Discussion 0066
NWS Weather Prediction Center College Park MD
528 PM EDT Sat Mar 15 2025

Areas affected...Middle & Eastern TN...Northeast MS...Northern
AL...Northwest GA...South-Central KY...

Concerning...Heavy rainfall...Flash flooding likely

Valid 152130Z - 160315Z

SUMMARY...Multiple lines of thunderstorms with moderate shield
precipitation between crossing already saturated/low FFG soil
conditions, likely to continue flash flooding risk through to
early overnight period.

DISCUSSION...A very complex surface pattern exists across the
middle MS Valley due to the back to back strong upper-level
shortwaves. This continues through depth with the EML from the
prior stronger closed low being modified by earlier convection
this morning across E TN/N MS; while a secondary dry slot is
starting to manifest across AR in the wake of the secondary
shortwave now maturing across S MO. As such, surface moisture
though worked over, remains across E TN/W KY/N MS with TDs still
in the upper 50s/lower 60s. However, strong LLJ in response to
the shortwave has allowed for the western branch of low level
moisture and warming at the boundary layer to wash through and
with steepening lapse rates from the new EML; an expanding area of
MUCAPE is developing across NE MS and W Middle TN in the wake of
the stronger cells further east. As such, there is an expectation
of the stronger forcing along the cold front and lifting surface
low across N MS to expand elevated thunderstorms along the leading
edge further into W Middle TN. MUCAPEs of 500-1000 J/kg will
increase over the next few hours and feed cells and given strong
low level moisture flux convergence allow for increasing rainfall
potential with 1-1.5"/hr rates possible. This is going to fall on
areas already saturated/flooded by earlier rounds of thunderstorms
(see below) and likely to exceed the compromised FFG values at or
below 1.5 at 1-3 hour time periods.

Ahead of this new development, the initial storms continue to
press eastward across E Middle TN into the Cumberland Plateau as
well as extending back as a pre-frontal convective line across N
AL and NE MS. A broad shield of moderate precipitation is likely
to continue between these two lines maintaining flooding
conditions through the late evening/early overnight period.=20=20
Cells to the east are starting to weaken a bit, with reducing
lightning mainly has area has only received advected higher
theta-E air from central AL/NE GA given cloud cover inhibiting
insolation throughout the day. Still, there is weak but
sufficient MUCAPEs into E TN and far S KY to maintain some. A
spot or two of 3-4" remains possible organization over the next
few hours. Rates of 1-1.5"/hr are probable given the broad,
strong LLJ pumping 1.5-1.75" TPW (mainly below 700mb) on 50+kts of
850mb southerly flow/WAA. As such, rainfall pattern will show
broad area of 2-3" across much of the eastern half of TN and
northern AL where multiple rounds will cross with embedded
weakening but intense showers to overtake those lower FFG
values/saturated soils in the region keeping flash flooding likely
through much of of the evening into early overnight period; but a
spot or two of 3-4" may result in considerable or even significant
flash flooding possible.

Gallina

ATTN...WFO...BMX...FFC...HUN...JAN...JKL...LMK...MEG...MRX...
OHX...

ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...

LAT...LON 37158440 36498387 35568421 34458484 33638532=20
33158642 32408895 32688965 33928905 35528824=20
36368765 36728673 37148538=20

$$
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