MESOSCALE PRECIPITATION DISCUSSION 0238...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
807 AM EDT THU MAY 26 2016
 
CORRECTED FOR GRAPHIC

AREAS AFFECTED...CENTRAL & SOUTHEAST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 261203Z - 261803Z
 
SUMMARY...AS CIN ERODES THIS MORNING, CONVECTION IS EXPECTED TO
INCREASE IN COVERAGE.  WITH SUBSTANTIAL INSTABILITY AND MOISTURE
IN PLACE, HOURLY RAIN RATES TO 2.5" AND LOCAL AMOUNTS OF 3-5"
COULD LEAD TO FLASH FLOODING.

DISCUSSION...WHAT WAS ONCE FORWARD PROPAGATING CONVECTION ACROSS
CENTRAL TX HAS BEEN SLOWING DOWN AS OF LATE AS ITS RELATED OUTFLOW
BOUNDARY HAS SLOWED DOWN, PER SURFACE OBSERVATIONS.  RADAR IMAGERY
REVEALS TWO HEAVY RAIN CORES NEAR AND AHEAD OF THE OUTFLOW
BOUNDARY ACROSS PORTIONS OF THE TX HILL COUNTRY/CENTRAL TX.  AHEAD
OF THIS FEATURE, A DEW POINT GRADIENT HAS SET UP SHOP FROM ROUGHLY
PORT ARTHUR TO AUSTIN TX.  PRECIPITABLE WATER VALUES ARE 1.7-2" IN
THIS AREA PER GPS VALUES, WITH SOUTH-SOUTHWEST 30 KTS OF INFLOW
PER VAD WIND PROFILES ADVECTING IN 2000-3500 MLCAPES INTO THE
REGION.  SPC MESOANALYSES INDICATE THAT BOTH MUCIN AND MLCIN ARE
ALREADY ERODING ACROSS CENTRAL AND SOUTHEAST TX.

THE MESOSCALE/CAM GUIDANCE, LED BY THE TRIO OF HRRR GUIDANCE AS
WELL AS THE 06Z NAM (4 KM) CONEST AND 00Z SPCWRF, APPEAR TO
INDICATE THE HEAVY RAINFALL POTENTIAL BEST IN THIS REGION, SHOWING
LOCAL AMOUNTS IN THE 3-5" RANGE, WHICH COULD FALL QUICKLY. THE
AVAILABLE MOISTURE SUPPLY SUPPORTS HOURLY RAIN RATES UP TO 2.5",
WHICH COULD BE EXCEEDED IN CELL MERGERS. THE 06Z GFS-BASED
GALVEZ-DAVISON INSTABILITY INDEX SHOWS INCREASING VALUES WITHIN
TIME HERE, RISING FROM 35 PAST 45 BY 18Z, IMPLYING NUMEROUS
SHOWERS AND THUNDERSTORMS ARE POSSIBLE BY 18Z. PULSE ACTIVITY
SHOULD MOVE EAST-NORTHEAST TO NORTHEAST AT ~ 30 KTS, THOUGH
ORGANIZED CONVECTIVE CLUSTERS WOULD TRACK MORE EAST TO
EAST-SOUTHEAST AT 25-35 KTS WHICH COULD LEAD TO THE MERGERS. 
ACTIVITY WOULD BE INITIALLY ELEVATED OVER THE DEW POINT BOUNDARY
BEFORE BECOMING MORE SURFACE-BASED LATER THIS MORNING INTO THIS
AFTERNOON.  FLASH FLOODING IS A CONCERN, PARTICULARLY WITHIN URBAN
AREAS WHERE DRAINAGE OF HEAVY RAINFALL IS A CONCERN, LIKE HOUSTON
TX.

ROTH

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

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

LAT...LON   32139757 31979568 30319472 29319514 29699756 
            30389863 31659864