Mesoscale Precipitation Discussion 887
NWS Weather Prediction Center College Park MD
337 AM EDT Sun Sep 23 2018

Areas affected...Eastern TX...Southwest AR...Northwest LA

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

Valid 230736Z - 231336Z

Summary...Moderate to heavy showers are expected to continue
across eastern Texas and parts of adjacent states through 8:30 am
local time ahead of a quasi-stationary front.  This additional
rainfall will only exacerbate ongoing flooding issues over
northeast Texas.

Discussion...Regional Doppler radar imagery scattered intense
showers and thunderstorms associated with a slow moving surface
low over northeast Texas.  There have been some reports of greater
than 2 inches of rainfall observed since midnight.  Ascent is
being aided by a nearby 500mb shortwave, converging 850mb flow,
and modest right entrance upper jet dynamics. 

The anomalously high PW values ahead of the slow moving cold front
across eastern Texas is indicative of a tropical airmass with deep
warm cloud layers and efficient rainfall processes.  PW values on
the order of 2.2 to 2.4 inches remain over this region ahead of a
stalled frontal boundary as reflected in recent GPS data and RAP
model analysis.  

An aggravating factor in the flooding potential is the very low
flash flood guidance values over the northern portion of the MPD
area in northeast Texas owing to the heavy rainfall over the past
2 days.  The latest suite of high res guidance now has a strong
signal for narrow swaths of 2 to 4 inch rainfall maxima extending
from the greater Houston area to west of Shreveport, which is
indicative of training convective activity.  Since the highest QPF
maxima are likely over areas with higher flash flood guidance
south of Interstate 20, flash flooding is considered possible.

D. Hamrick

ATTN...WFO...FWD...HGX...LCH...OUN...SHV...TSA...

ATTN...RFC...ABRFC...LMRFC...WGRFC...

LAT...LON   34049549 33979425 33539327 32759292 32329289
            31109341 30099359 29239374 29139424 29159468
            29099530 29269557 29779579 30649573 31429574
            32229602 32759649 32889676 33069689 33589676
            33829628