MESOSCALE PRECIPITATION DISCUSSION 0135...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1029 AM EDT THU APR 21 2016
 
AREAS AFFECTED...SOUTHEAST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 211425Z - 211725Z
 
SUMMARY...THUNDERSTORMS FORMING AHEAD OF AN OUTFLOW BOUNDARY WHICH
IS SLOWING AS IT ENTERS SOUTHEAST TX COULD LEAD TO HOURLY RAIN
RATES UP TO 1.75".  FLASH FLOODING IS POSSIBLE WITHIN A SATURATED
AREA.

DISCUSSION...THE 14Z MESOSCALE ANALYSIS SHOWS A DEW POINT GRADIENT
JUST INLAND OF THE TX COAST AND OFFSHORE THE LA COAST, WHICH IS
PARTIALLY DUE TO AN OUTFLOW BOUNDARY FROM EARLY MORNING LA
CONVECTION.  MLCAPES OF 1000-2000 J/KG LIE SOUTH OF THIS FEATURE. 
CONVECTION HAS BEEN FORMING NORTHWEST OF THIS BOUNDARY.  TO ITS
WEST, AN OUTFLOW BOUNDARY FROM WHAT HAD BEEN A FADING SQUALL LINE
IS MOVING INTO THE REGION, WHICH HAS SHOWN SIGNS OF SLOWING SINCE
10Z.  GFS-BASED FORWARD PROPAGATION VECTORS SHOWED THE POTENTIAL
FOR SLOWING -- LONG-TERM PROGRESSION HAS FALLEN FROM 35 KT TOWARDS
25 KTS.  PRECIPITABLE WATER VALUES ARE NEAR 1.4", AND INFLOW AT
850 HPA (NEAR CLOUD BASES) IS WEST-SOUTHWEST AT ~25 KTS.  HOURLY
RAIN RATES HAVE RECENTLY REACHED 1" LOCALLY NORTHWEST OF
IAH/HOUSTON INTERCONTINENTAL AIRPORT.

SOME OF THE CAM GUIDANCE SHOWS THE POTENTIAL FOR LOCALIZED 2-3"
AMOUNTS, WHICH COULD FALL QUICKLY.  THE AVAILABLE PRECIPITABLE
WATER REGIME ALLOWS FOR HOURLY RAIN RATES UP TO 1.75", HIGHER
WHERE CELL MERGERS OCCUR.  WHILE MUCH OF THE CONVECTION CURRENTLY
APPEARS TO BE PULSE IN NATURE, ORGANIZED SEGMENTS WOULD CONTINUE
PUSHING SOUTHEAST AT 20-25 KTS OVER THE NEXT FEW HOURS, WHICH
SHOULD MOVE THE OLD SQUALL LINE INTO THE GULF OF MEXICO.  MUCH OF
THE REGION HAS SEEN HEAVY RAINFALL OVER THE PAST 3-4 DAYS, SO
SOILS ARE SATURATED.  LOCAL AMOUNTS IN THE 2-3" RANGE COULD LEAD
TO FLASH FLOODING.  DUE TO FORECAST UNCERTAINTY, USED A THREE HOUR
WINDOW.

ROTH

ATTN...WFO...HGX...LCH...

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

LAT...LON   30969488 30839405 30419381 29919381 29619405 
            29039531 29229626 29749663 30249590