MESOSCALE PRECIPITATION DISCUSSION 0640
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
223 AM EDT MON AUG 07 2017

AREAS AFFECTED...CENTRAL TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 070622Z - 071222Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE EXPANDING IN COVERAGE
ACROSS CENTRAL TX.  HOURLY RAIN TOTALS UP TO 2.5" AND LOCAL
AMOUNTS TO 5" ARE POSSIBLE.

DISCUSSION...A WEST-NORTHWEST/EAST- SOUTHEAST ORIENTED BAND OF
THUNDERSTORMS IS TRYING TO FORM ACROSS CENTRAL TX, MOVING
EAST-SOUTHEAST AT ~15 KTS, WHICH HAS SHOWN SOME BROADENING IN THE
COLD CLOUD TOPS ON NON-OPERATIONAL GOES-16 INFRARED IMAGERY.  THIS
IS OCCURRING NORTH OF WHAT HAS BEEN A PROGRESSIVE OUTFLOW BOUNDARY
WHICH IS LOCATED SOUTH OF SAN ANGELO.  INFLOW AT 850 HPA IS
INCREASING IN THIS AREA, NOW UP TO 20 KTS PER THE DEL RIO TX VAD
WIND PROFILE.  EFFECTIVE BULK SHEAR IS ~20 KTS.  PRECIPITABLE
WATER VALUES OF 1.6-2.1" EXIST IN THIS AREA PER GPS VALUES.
   
RAP GUIDANCE SHOWS A SLOWING OF THE SOUTHWARD MOVEMENT OF THE
OUTFLOW BOUNDARY AS THE INFLOW AT 850 HPA INCREASES TOWARDS 35 KTS
AND BEGINS TO VEER.  AS IT MOVES INTO SOUTHEAST TX, THE RAINFALL/
THUNDERSTORM BAND COULD BROADEN AS IT ENCOUNTERS 79F DEWPOINTS
NORTHWEST OF HOUSTON TX.  FORWARD PROPAGATION VECTORS SUGGEST THAT
THE BOUNDARY SHOULD TRY TO PROGRESS SOUTH-SOUTHEAST AT 10-15 KTS,
WHICH SHOULD LIMIT OVERALL TOTALS.  SOME BACKBUILDING AND EASTWARD
PROGRESSION IS EXPECTED WITH TIME.  THE GUIDANCE THAT APPEARS TO
BE CAPTURING THIS ACTIVITY THE BEST RIGHT NOW IS THE 00Z WRF NSSL,
WHICH SHOWS LOCAL MAXIMA OF 5-6", WHICH COULD BE A TOUCH HIGH. 
HOURLY RAIN TOTALS UP TO 2.5" ARE POSSIBLE WHERE CELLS TRAIN OR
MERGE ALONG WITH LOCAL MAXIMA AROUND 5" OVER THE NEXT SEVERAL
HOURS, WHICH COULD EXCEED THE HIGH FLASH FLOOD GUIDANCE VALUES IN
THE REGION.

ROTH

ATTN...WFO...EWX...FWD...HGX...SJT...

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

LAT...LON   31649995 31479907 31139780 31439591 30259534
            29319597 29019775 29289944 29880136 30810118