Mesoscale Precipitation Discussion 0885...Corrected
NWS Weather Prediction Center College Park MD
1029 PM EDT Sat Sep 22 2018

Corrected for Area affected

Areas affected...Southeast OK and Northeast TX

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

Valid 230218Z - 230718Z

Summary...Moderate to heavy showers are expected to continue
across already saturated ground into the early morning hours. 
This additional rainfall will only exacerbate ongoing flooding
issues over northeast Texas and southeast Oklahoma.

Discussion...Regional Doppler radar imagery is indicating a
gradual increase in shower activity associated with a slow moving
surface low over northeast Texas.  Although infrared satellite
imagery is not particularly impressive over this area, there is
some gradual expansion of colder cloud tops near the Red River,
which is coincident with the higher rainfall rates that are on the
order of an inch per hour.  Ascent is being aided by a nearby
500mb shortwave, converging 850mb flow, and 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.  GPS derived
PW values are on the order of 2.2 to 2.4 inches, which is
supported by the 00Z SHV sounding with a 2.33 inch PW.  

An aggravating factor in the flooding potential is the very low
flash flood guidance values owing to the heavy rainfall over the
past 2 days, in some cases under 1 inch in 3 hours.  The latest
suite of high res guidance has overall been too quick to develop
heavier QPF, however recent radar trends would support additional
rainfall amounts of 1 to locally 3 inches through 2am local time. 
The ARW and NMMB appear to have a reasonable depiction of the
expected evolution, and flash flooding is considered possible.

D. Hamrick

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

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

LAT...LON   34339632 34289527 34119451 33689386 33079355
            32589363 32019391 31249444 31009509 31099555
            31559575 32199598 32759649 32939692 33069737
            33399776 33999765 34229711