MESOSCALE PRECIPITATION DISCUSSION 0586
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
702 PM EDT SAT AUG 20 2016
 
AREAS AFFECTED...SOUTH-CENTRAL TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 202300Z - 210100Z
 
SUMMARY...SMALL BANDS OF SLOW-MOVING THUNDERSTORMS WITH VERY
INTENSE RAINFALL GRADUALLY BECOMING BETTER ORGANIZED NEAR SAN
ANTONIO. FLASH FLOODING IS LIKELY.

DISCUSSION...A VERY WELL-DEVELOPED MCV WITH A STRONGLY
CONCENTRATED AREA OF EXTREMELY HEAVY RAINFALL IS JUST EAST OF THE
AUSTIN AREA AT THIS TIME. THE SOUTHWEST FLANK OF THE
MCV...INCLUDING THE SAN ANTONIO METROPOLITAN AREA...IS BECOMING
INCREASINGLY ACTIVE AS VERY MOIST AND UNSTABLE AIR POOLS UP AGAIN
CONFLUENT LOW TO MID LEVEL FLOW AND AN AXIS OF RATHER STRONG
DIFFERENTIAL HEATING.

CLOUD TOPS ARE RAPIDLY COOLING AND CELL MOTION IS VERY SLOW NEAR
THIS EFFECTIVE BOUNDARY. THE POTENTIAL FOR VERY HEAVY RAINFALL AS
MENTIONED WITH EARLY MPDS IS EXPECTED TO BECOME INCREASINGLY
LIKELY WITH THE APPROACH OF EVENING GIVEN A VERY FAVORABLE
ENVIRONMENT FOR INTENSE CONVECTIVE RAINFALL.

PWATS ARE NEAR 2.25 INCHES...AND WITH SUCH A DEEP MOIST
COLUMN...THE CONVECTION WILL BE EXTREMELY EFFICIENT IN GENERATING
ENHANCED RAINFALL RATES THAT MAY APPROACH OR EXCEED 3 INCHES/HR.

CONVECTION WILL BECOME MORE FOCUSED AROUND THE SOUTHWEST FLANK OF
THE MCV AS LOW LEVEL INFLOW INCREASES THIS EVENING AND IS
INTERCEPTED BY THE AFOREMENTIONED BOUNDARY AND AXIS OF LOW/MID
LEVEL CONFLUENCE.

HIRES GUIDANCE LED BY THE HRRR/HRRRP SUGGESTS AS MUCH AS 3 TO 5
INCHES OF RAIN JUST OVER THE NEXT 2 TO 3 HOURS LOCALLY AROUND SAN
ANTONIO AND ADJACENT AREAS TO THE SOUTH.

FLASH FLOODING WILL BE LIKELY...AND NEW MPDS WITH UPDATES WILL BE
ISSUED AS CONDITIONS EVOLVE THIS EVENING.

ORRISON

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

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

LAT...LON   29859653 29199676 28679715 28329789 28179887 
            28209945 28400018 29000057 29230019 29469907 
            29599817 29779744