AWUS01 KWNH 282144
FFGMPD
TNZ000-MSZ000-LAZ000-MOZ000-ARZ000-TXZ000-290330-

Mesoscale Precipitation Discussion 1202
NWS Weather Prediction Center College Park MD
444 PM EST Sat Dec 28 2024

Areas affected...far southeastern TX into lower/middle MS Valley

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

Valid 282142Z - 290330Z

SUMMARY...An axis of training heavy rain is expected to produce
scattered areas of flash flooding from far southeastern TX into
the lower/middle MS valley through 03Z. Rainfall rates of 1 to 2
in/hr (locally higher) are expected.

DISCUSSION...Regional radar imagery at 0415Z showed a NE to SW
oriented axis of thunderstorms tracking slowly toward the east
from southeastern AR into LA and far southeastern TX. Cell speeds
were slowest in the vicinity of a quasi-stationary front that was
analyzed from western TN/northwestern MS into southeastern AR,
with a surface low becoming better defined along the front roughly
35 miles west of Monroe, LA. South of this low, a cold front was
moving southeast/east but cells ahead of the front were more
intense than those to the north with generally colder cloud tops,
greater lightning frequency and higher MRMS hourly rainfall
estimates. This was due to the numerous coverage of cells
(including supercells) along/ahead of the cold front near the
lower Sabine River to the MS River, with mergers and brief
training coupling with greater individual cell organization. SPC
mesoanalysis data from 21Z showed 1500 to 2500+ J/kg MLCAPE in
place from the LA/MS border into the southeastern TX Coastal Plain.

Water vapor imagery showed that a strong shortwave trough over
east-central TX was beginning to take on a negative tilt.
Increasing diffluence and divergence aloft, downstream of the
shortwave, will overspread the lower and middle MS Valley through
the late evening. As this happens, the surface low over northern
LA is expected to organize and track northward up the MS River
Valley. The southward extending cold front will pick up speed and
sweep southeastward across southeast TX and LA. While the forward
speed of the cold front will limit flash flood potential across TX
and portions of LA, multiple rounds with cells in the pre-frontal environment/mergers and brief training will still pose an isolated
flash flood threat for these regions.

Farther north, slow movement of the quasi-stationary front and
increasing low level moisture transport ahead of the organizing
surface low will wrap moisture back to the west, north of the low,
with an expected longer duration of rainfall rates of 1-2 in/hr
and perhaps the highest additional rainfall totals for the region
through 03Z, on the order of 2 to 4+ inches from near the MS River
into northwestern MS and southwestern TN. FFG values are lower for
these northern areas 2-3 inches in 3 hours, and therefore, flash
flooding appears likely.

Otto

ATTN...WFO...HGX...JAN...LCH...LIX...LZK...MEG...SHV...

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

LAT...LON 36228927 36068867 35498838 34708850 33298883
32028940 30369057 29339295 29559483 30789473
31489371 32869292 33719206 35299093 36088987

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