Mesoscale Precipitation Discussion 0215
NWS Weather Prediction Center College Park MD
211 PM EDT Fri May 03 2024
Areas affected...Central Mississippi and far West-central
Alabama...
Concerning...Heavy rainfall...Flash flooding possible
Valid 031810Z - 032330Z
SUMMARY...Converging outflow boundaries to support enhanced
short-term ascent while aligning favorably to deep layer steering
flow to allow for pockets of 2-3.5" totals in 1-3 hrs resulting in
possible localized incidents of flash flooding.
DISCUSSION...A pre-frontal pressure trough extending along/ahead
of trailing mid-level trough out of the Great Lakes into the
approaching shortwave across northwest Arkansas has active
thunderstorms along the leading edge of last-evening MCS across
OK/AR. To the south, a similar outflow is pressing
north-northeast along the edge of the MCS/MCV across southeast LA.
Between the two, fairly clear skies through morning has resulted
in increasingly unstable environment across central MS into W/NW
AL with an expanding area of 1000-1500 MLCAPE mainly along the
northern boundary where modest low to mid-level moisture has
advected into the area.
The forward propagation of each boundary combined weakening
capping has is starting to destabilize the area of concern while
also supporting a recent uptick in convective vigor with
overshooting tops starting to cool below -65C. Deep layer
moisture is generally coincident and starting to increase above
1.5" with spots of 1.75" further west as the mid-levels have
moistened. As such, strong convergence will support solid
moisture flux into the updrafts for 1.5-1.75"/hr rates. Forward
propagation is likely to limit broader scale areas of high
rainfall totals. However, as the two outflow boundaries converge
across central MS, further updraft strength as well as potential
cell mergers may result in localized sub-hourly 2" totals. Given
the orientation of the merging lines is laid out favorably to
deeper layer cell motions, there is a hint of prolonged duration
from repeating or expansion of the moderate post-shield rainfall
for localized spots of 2-3.5" totals in 1-3 hours. These
short-term rates and 3hr totals are near the FFG values in the
area (given recent average rainfall and soil saturation values
about 50-60% and near normal/slightly above normal). So flash
flooding is considered possible through evening and is more likely
to be limited to low-end, spotty in nature coverage and more
probable if overlapping urban and/or high-prone flashy creeks and
streams.
Gallina
ATTN...WFO...BMX...JAN...MEG...MOB...
ATTN...RFC...LMRFC...SERFC...NWC...
LAT...LON 34008802 33708739 32708763 32058831 31608915
31519018 31819105 32659104 33449020 33858903
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