Mesoscale Precipitation Discussion 0630
NWS Weather Prediction Center College Park MD
236 AM EDT Sat Aug 11 2018

Areas affected...north Texas

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

Valid 110634Z - 111200Z

Summary...Heavy rain is expected to overspread locations near and
south of the Dallas-Fort Worth Metroplex between about 08-11Z.
Slow moving storms will have the potential of generating 2-3 in/hr
rainfall rates and possible flash flooding.

Discussion...At 06Z, a combination of GOES 16 infrared imagery,
VAD wind plots at 700 mb and RAP analyses placed a low-mid level
circulation west of Fort Worth and just south of I-20.
Disorganized and slow moving convection was noted on the southeast
side of the circulation, slowly spreading north, with KGRK radar
estimated rainfall rates of 2-3 in/hr ending 06Z just west of I-35
to the south of Waco. GPS precipitable water values near and south
of Dallas-Fort Worth were 1.9 to 2.1 inches with weak MUCAPE of
500-1000 J/kg per the most recent SPC mesoanalysis valid at 06Z.
Earlier rainfall from 03-04Z west of San Antonio contained rain
rates near 3 in/hr with similar environmental variables as what is
currently in place across portions of north-central TX.

850 mb VAD winds from KGRK and KEWX were 20-30 kt (about 5-15 kt
stronger than RAP analyses) with a south-southwesterly direction,
which is stronger than the 850-300 mb mean flow of ~15 kt. This
should help to support repeating and slow moving heavy rain cores
southeast of and just ahead of the 700-500 mb low. Flash Flood
Guidance in and around Dallas-Fort Worth is 2-3 inches in 3 hours
as well as to the south, over Ellis and Navarro counties, where at
least 2-4 inches of rainfall has fallen over the past 24 hours. An
additional 2-4 inches of rainfall is expected in a few locations
across some of these same locations over the next 3-6 hours which
could cause flash flooding.

Otto

ATTN...WFO...FWD...

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

LAT...LON   33259678 32939582 31709581 30989663 31029747
            31799827 32439837 33049792