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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AWUS01 KWNH 261057
FFGMPD
LAZ000-TXZ000-261655-

Mesoscale Precipitation Discussion 0732
NWS Weather Prediction Center College Park MD
656 AM EDT Fri Jul 26 2024

Areas affected...Portions of Eastern TX into West-Central and
Southwest LA

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

Valid 261055Z - 261655Z

SUMMARY...Additional areas of heavy rainfall should tend to
continue this morning across areas of eastern TX and west-central
to southwest LA. Flash flooding will remain likely including
continued concerns for locally considerable urban flash flooding.

DISCUSSION...The early-morning GOES-E IR satellite imagery shows a
rather impressive cold-topped convective wedge (with tops to -60
to -65 C) near the upper TX coast and generally advancing east of
Galveston Bay to the immediate offshore waters, However, radar
imagery does show some of the heavier showers and thunderstorms
with this still impacting some inland areas of southeast TX, with
the activity also encroaching on southwest LA.

An elongated axis of vort energy is noted along much of the middle
and upper TX coast and up across interior areas of eastern TX
around the eastern flank of a broader mid-level trough over the
southern Plains. This energy is interacting with a very deep
tropical airmass and axis of stronger instability that is pooled
up across the northwest Gulf of Mexico and inland to some extent
over far southeast TX and far southwest LA. In fact, MLCAPE values
of 1500 to 2500 J/kg are noted across these areas with PWs of 2.0
to 2.25 inches.

The ongoing convection is likely to continue going through the
morning hours given the set-up which is also being facilitated by
favorable right-entrance region upper-level jet dynamics and a
convergent southerly low-level jet of 20 to 30 kts that is nosed
up along to the TX/LA border.

Generally the focus for the heaviest rainfall totals in near-term
going through at least mid-morning should continue to be over
areas of far southeast TX which over the next 1 to 3 hours will
likely include portions of the Beaumont-Port Arthur vicinity, but
this convection is expected to advance into some areas of
southwest LA, and eventually the Lake Charles vicinity may come
under impacts from this convection. Some of the rainfall rates
with these cells are likely to reach 2 to 3 inches/hour. Galveston
Airport in the last hour (4AM to 5AM CDT) alone reported 2.38
inches as these storms crossed through.

Additional areas of heavy rain are also noted farther north away
from the coast across parts of eastern TX and into west-central LA
where antecedent conditions are already quite wet and locally
saturated from recent heavy rainfall. High streamflows are noted
more regionally also via the latest USGS gauge data.

Therefore, with the potential for an additional 3 to 5+ inches of
rain locally this morning, and the sensitive ground conditions,
additional areas of flash flooding are likely.

Orrison

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

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

LAT...LON 32019350 31809281 31189243 30399238 29679263
29599344 29339437 28809551 28989604 29549595
30159575 30819518 31689421
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