AWUS01 KWNH 182157
FFGMPD
MSZ000-LAZ000-TXZ000-190400-

Mesoscale Precipitation Discussion 1157
NWS Weather Prediction Center College Park MD
455 PM EST Mon Nov 18 2024

Areas affected...Far Southeast TX...Southwest to Central LA

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

Valid 182200Z - 190400Z

SUMMARY...An increase in coverage of showers and thunderstorms can
be expected going into the evening hours. Heavy rainfall rates and
potentially some areas of cell-training may foster some localized
potential for flash flooding.

DISCUSSION...As a deep upper-level trough pivots northeastward
through the central Plains and toward the Midwest, a cold front
will be gradually approaching the northwest Gulf Coast region.
This front will be interacting with a very moist and increasingly
unstable airmass out ahead of it this evening, and the result is
expected to be an increase in the coverage of heavy showers and
thunderstorms.

PWs are quite high right now across southeast TX with values near
or slightly above 2 inches, and these magnitudes are as much as 2
to 3 standard deviations above normal for this time of the year.
Meanwhile, MLCAPE values have risen to as much 1000 to 1500 J/kg
and thus a moderate level of buoyancy has already pooled ahead of
the front with the aid of daytime heating.

A fairly strong southerly low-level jet of 30 to 40+ kts will be
maintaining somewhat enhanced moisture transport off the Gulf of
Mexico ahead of this front this evening. This coupled with the
level of instability and favorable bulk shear should yield
relatively organized bands or clusters of convection, including
potentially some supercell activity, that will be capable of
producing rainfall rates of 1 to 2 inches/hour. Initially the
activity will be more focused over areas of far southeast TX, but
should in time concentrate increasingly over southwest to central
LA.

Some of the more organized activity may involve some cell-training
as the convection becomes aligned with the deeper layer mean flow,
and this may result in the potential for locally excessive totals.
The 12Z/18Z HREF guidance supports some 2 to 4 inch rainfall
amounts with isolated heavier totals. A localized and mostly urban
flash flood threat will exist as these bands of convection come
through this evening.

Orrison

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6jucQIqEYwpxCvflmYFiKiE8VFtMqgbz0oaNbKbL_kmV0P55GzA3aCGc1dkx8VLC1nES=
J4HizpGEPbfo3Q_5v0bbbow$  for graphic product...

ATTN...WFO...JAN...LCH...LIX...SHV...

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

LAT...LON   32289212 32109155 31229155 30039244 29619285=20
            29709339 29649395 29909426 30469430 31049394=20
            32059292=20

=3D =3D =3D
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