AWUS01 KWNH 241246
FFGMPD
LAZ000-TXZ000-241845-

Mesoscale Precipitation Discussion 0716
NWS Weather Prediction Center College Park MD
845 AM EDT Wed Jul 24 2024

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

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

Valid 241245Z - 241845Z

SUMMARY...Slow-moving bands of locally training showers and
thunderstorms will be capable of producing extremely heavy
rainfall rates and excessive totals going through midday. At least
scattered instances of flash flooding, including urban impacts,
are likely to materialize.

DISCUSSION...The early morning GOES-E IR satellite imagery shows a
loosely organized complex of convection focused near the Upper TX
coast and overspreading adjacent areas of far southeast TX and
into southwest LA. The convection is associated with a weak
mid-level shortwave perturbation and an associated low-level
trough while interacting while also interacting with a very moist
and moderately unstable airmass that is pooling north from the
Gulf of Mexico.

MLCAPE values around the southeast flank of the vort energy and
adjacent to some of the convective bands is on the order of 1000
to 1500 J/kg, with the main axis of this noted from near the Upper
TX coast northeastward into far southwest LA. The low-level flow
is rather confluent in general over the northwest Gulf of Mexico
with about 20 to 25 kts of southwesterly 850 mb flow aiming into
southwest LA.

This low-level flow is forecast by the RAP guidance to increase
over the next few hours to as much as 30+ kts which will favor a
general uptick in not only moisture transport, but also speed
convergence. This should favor a persistence and localized
expansion of the ongoing convective activity, with a tendency for
this to become locally more concentrated over southwest to central
LA, while also lingering potentially farther back to the southwest
over the Upper TX coast where low-level convergence near a surface
trough will be well-established.

Some of the most recent hires model guidance and surface
observations suggest a wave of low pressure may be attempting to
form over southeast TX in association with this energy, and this
may help to maintain a semi-organized convective threat going into
the afternoon hours.

PWs over the region are deeply tropical in nature, with values of
2.25 to 2.5 inches, and this coupled with the level of instability
and forcing should promote rainfall rates reaching 2 to 3
inches/hour with the stronger cells. There will be concerns for
cell-training with these slow-moving linearly oriented bands of
convection, and some rainfall totals through midday may reach as
high as 4 to 6 inches where this occurs. Given the rainfall
potential and increasingly wet/sensitive antecedent conditions,
there will likely be at least scattered instances of flash
flooding. This will include impact concerns to the more urban
corridors which will include areas from Port Arthur, TX over to
Lake Charles, LA.

Orrison

ATTN...WFO...HGX...LCH...SHV...

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

LAT...LON   31639308 31459209 30469195 29689231 29699309 
            29619367 29549402 29379448 29539458 29729452 
            30179407 30979376 
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