Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue May 09 2023 18:11:19

AWUS01 KWNH 091811
FFGMPD
MSZ000-LAZ000-TXZ000-100010-

Mesoscale Precipitation Discussion 0246
NWS Weather Prediction Center College Park MD
210 PM EDT Tue May 09 2023

Areas affected...southeastern TX into central/southern LA

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

Valid 091810Z - 100010Z

Summary...Slow moving and training convection with localized
rainfall rates of 2-3 in/hr is expected across the southern half
of LA, perhaps affecting portions of southeastern TX through 00Z.
Areas of flash flooding may result with 6-hr rainfall totals of
3-5 inches, locally higher.

Discussion...18Z regional radar and visible satellite imagery
showed a pronounced low to mid-level vorticity max 70 miles of
Galveston Bay, tracking toward the western LA coast. Thunderstorms
have been arcing northward through southeastern TX and
southwestern LA on outflow with additional storms noted out ahead
over south-central and southeastern LA. Recent GPS data indicated
precipitable water values of 1.5 to 1.8 inches across the region
and the 17Z SPC mesoanalysis showed MLCAPE of 1500 to 2000+ J/kg.
While not particularly strong across the Gulf Coast, mid to upper
level flow of 20-40 kt was fairly diffluent ahead of the
approaching offshore circulation.

While an isolated flash flood threat will exist in the short term
with ongoing convection over eastern TX and LA, an additional
threat will exist near and east of the approaching vorticity max
as it moves ashore between 21-00Z. Recent RAP forecasts have shown
a localized corridor of 850-700 mb winds east of the circulation
center of 30-40 kt as the vorticity center nears the coast.
Enhanced low level convergence, sufficient upper level support and
instability are expected to support multiple rounds of
thunderstorms over south-central to southeastern LA later this
afternoon into the evening hours. Meanwhile, a localized flash
flood threat may exist with the circulation center itself where
individual storm motions are likely to be slow at less than 10 kt
following the deeper layer mean wind. While relatively high flash
flood guidance may mitigate the degree of runoff concerns, there
will be the potential for very high rainfall rates which could
overcome mostly dry antecedent conditions.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!5wb4v4l1NBZqmZc0r38k9EQ2tRr2BpXdN7H9XbyKV3OGSejF-V717PEZYqazgFpDm6-B=
-H7t9edeA6vugAcsg5Act7s$  for graphic product...

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

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

LAT...LON   31889413 31659312 31209179 30889080 30479007=20
            30118985 29539004 29109053 29009106 29319272=20
            29369439 30369508 31509504=20

=3D =3D =3D
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