Subj : MESO: Heavy rain - floodi
To   : All
From : Mike Powell
Date : Sat May 20 2023 07:38:00

AWUS01 KWNH 201055
FFGMPD
TXZ000-201400-

Mesoscale Precipitation Discussion 0317
NWS Weather Prediction Center College Park MD
655 AM EDT Sat May 20 2023

Areas affected...South Texas...

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

Valid 201100Z - 201400Z

SUMMARY...Waning MCS still poses short-term intense rain-rates
(2.5"/hr) to pose low-end risk of flash flooding particularly
along I-37.

DISCUSSION...RADAR and GOES-E IR denote increased forward
propagation of leading edge of mature/waning MCS across South
Texas.  GOES-E WV denotes less favorable upper-level pattern is
starting to wash over from the southwest, but there remains a
small window of opportunity to maintain strong moisture flux
convergence and stronger updrafts capable of intense sub-hourly
rates that would near FFG, particularly if it can maintain itself
entering urban areas surrounding Corpus Christi.

RAP analysis suggests a well of remaining uncapped instability up
to 1500 J/kg of MLCAPE across eastern South Texas, with weak
southeasterly flow from surface to cloud base aiding to increased
forward propagation, but also convergence needed to maintain
stronger updrafts.  Tds in the low to mid-70s and a tight
850-700mb Td gradient has been corralling the system along I-37. 
MCV appears to lifting away toward the northeast, so weak veering
is supporting some southwesterly advection in the low levels as
well, but probably not much to maintain the system for much more
than a few hours, without shifting the focus westward toward the
Rio Grande Valley.  So with ample deep moisture up to 2" in total
PWat, rates of 2-2.5"/hr should be able to maintain for 2-3 hours
as the line reaches the coast.  MRMS Flash response upstream,
suggests these similar rates in short-duration should produce
200-400 cfs of pluvial flooding, which may be increased if the
system can hold together through the Lower Nueces River Basin into
urban areas near Corpus Christi. 

Gallina

ATTN...WFO...BRO...CRP...EWX...

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

LAT...LON   28759813 28229734 27799701 27519721 27279749 
            27209829 27469860 27829876 28479870 

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