Mesoscale Precipitation Discussion 0817
NWS Weather Prediction Center College Park MD
415 AM EDT Mon Sep 10 2018

Areas affected...Deep South TX and Central TX coastline...

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

Valid 100815Z - 101415Z

SUMMARY...Slow moving/highly efficient storms capable of isolated
flash flooding through early morning possible. 

DISCUSSION...GOES-16 3.9um loop detects a low level MCV shearing
SSW out of the convective complex from S Maverick into Old Mexico,
with the 850mb convergence axis angling SW dotted with
overshooting tops in the cycling warm/cooling IR top across Deep
South Texas.  WV suite also shows a nicely anticyclonic shaped
outflow feathering within the speed divergent/slightly diffluent
3H 50kt jet emanating from the complex into the Hill
Country...continuing to provide excellent outflow and UVV support
for any convection that has/will develop.  Deep moisture remains
with nearly saturated profiles per soundings/RAP forecast
soundings through the outlined area with 14-15Kft depth for warm
cloud and highly efficient rainfall production.  Given mean mixing
ratios of 16 to near 18 kg/kg (near the coast) and total PWATs
through this layer over 1.5" (2.2-2.4 total), rates of 2-2.5"/hr
are possible currently.  At this point, best cells are propagating
NNE due to cold pool generation over the Rio Grande Valley, which
could limit totals a bit (2-3").  

Currently, the best convergence is shifting toward the coast where
surface flow is strengthening slightly before sun-up and
frictional convergence is enhancing the updrafts.  IR tops over
Padre island off Kenedy county toward Nueces county continue to
expand/cool.  It is in coastal Nueces that FFG values are the
lowest but reduced values extend as far north along the coast as
Port Lavaca.  Hi-Res CAMs are suggestive of further convective
expansion toward the north with some enhancement on Western Gulf
banded features potentially adding some training to increased
local totals.   There is some uncertainty as the cold pool over
central Deep South Texas...may push the best convergence off shore
(as presented by the NAM Conest and ARW/ARW2).  Still the
threat/probabilities and trends suggest this may be over done,
given the saturated profiles/general weakness of the cold
pool/outflow.   As such totals of 2-4" are possible with some of
these cells and promote possible isolated flash flooding
conditions over the next 5-6hrs.

Gallina

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

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

LAT...LON   29169635 29089608 28769571 28429637 27939699
            27319727 26719729 26199714 25929712 25799737
            25979784 26049824 26259878 26389906 26619927
            27009949 27309959 27609967 27829994 28350031
            28720002 28819911 28509827 28959767 29079733