Mesoscale Precipitation Discussion 0101
NWS Weather Prediction Center College Park MD
450 AM EDT Fri Mar 15 2024

Areas affected...Southern AR...Northwest MS...surrounding portions
of LA/TX

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

Valid 150850Z - 151400Z

Summary...Favored training of deep convection for the next several
hours may result in additional totals of 2-4". Scattered instances
of flash flooding are likely.

Discussion...Resurgence of deep convection is well underway over
the Ark-La-Tex and downstream portions of southern Arkansas, as
seen by GOES-East infrared cold cloud tops. This is occurring
along an outflow boundary on the southwestern flank of a decaying
MCS, but a favorable environment should encourage increased
training over the next several hours. This mesoscale environment
is characterized by ML CAPE of 1000-2000 J/kg, PWATs of 1.5-1.8
inches (near the max moving average, per SHV sounding
climatology), and deep layer shear of 30-50 kts. In addition, a
highly favorable coupled overlap of 850 mb convergence (moderate
southwesterly low-level moisture transport) and 250 mb divergence
(diffluence downstream of subtropical jet streak over south TX and
within the right-entrance region of polar jet streak over the
northeast US) is likely to maintain deep convection. Convection
has already begun to train from WSW to ENE, and southern AR into
northwest MS are favored to see the most precipitation over the
next 3-5 hours.

The 00z HREF has a better handle of the ongoing convection than
more recent HRRR runs, suggesting localized totals of 2-4" through
15z (per the HREF PMM). The corresponding 3" neighborhood
exceedance probabilities are as high as 30-50% (maximized through
12z), but much of this rainfall has likely already occurred (with
MRMS indicating 2-3" hourly totals over the past hour) as CAMs are
often too slow with these dynamic convective processes. Even
still, given the favored environment with continued training of
convection, expect additional amounts of at least 1-3". This is
likely to result in scattered instances of flash flooding over the
next several hours, despite relatively high FFGs of 2.5-3.5".

Churchill

ATTN...WFO...JAN...LZK...MEG...SHV...

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

LAT...LON   34518884 33528894 32768986 32669231 32659359
            32679423 32769472 33149490 33749447 34239314
            34199060