MESOSCALE PRECIPITATION DISCUSSION 0460
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EDT THU AUG 20 2015
 
AREAS AFFECTED...MIDDLE TX COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 201500Z - 201900Z
 
SUMMARY...THUNDERSTORMS WITH HEAVY RAINFALL CONTINUE MOVING DOWN
THE TX COASTLINE.  FLASH FLOODING REMAINS POSSIBLE.

DISCUSSION...A BROAD MESOCYCLONE NEAR THE TX/MEXICO BORDER IS
CONTROLLING THE FLOW PATTERN IN THE REGION MORE THAN PREVIOUS RAP
GUIDANCE INDICATED.  THIS BROADER CIRCULATION HAS LED TO A SMALLER
MESOCYCLONE MOVING INTO PORT LAVACA RECENTLY, WHICH HAS FORCED THE
LOW-LEVEL FLOW TO BE MORE CONVERGENT THAN FORECAST.  PRECIPITABLE
WATER VALUES REMAIN BETWEEN 2-2.5" IN THIS REGION, WITH 850 HPA
INFLOW OF ~20 KTS.  MLCAPES OF 3000-4000 J/KG LIE ACROSS THE
MIDDLE TX COAST AND JUST OFFSHORE.

SINCE THE GUIDANCE HAS STRUGGLED WITH THEIR MASS FIELDS, WILL
ATTEMPT TO USE RECENT RADAR/ SATELLITE TRENDS AND THE MESOSCALE
QPF OUTPUT TO MAKE AN ASSESSMENT.  THE MATURE MCS IS EXPECTED TO
CONTINUE MOVING DOWN THE COAST AT ~10 KTS AS AN OUTFLOW BOUNDARY
CONTINUES MOVING SOUTHWESTWARD.  THE MESOSCALE QPF GUIDANCE
GENERALLY INDICATES THAT LOCAL 4" AMOUNTS REMAIN POSSIBLE AFTER
15Z.  WITH HOURLY RAIN RATES UP TO 3" INDICATED BY RADAR RECENTLY,
THE RAINFALL COULD FALL QUICKLY.  THE 06Z NEIGHBORHOOD
PROBABILITIES SHOW A WEAKER SIGNAL ALONG THE MIDDLE TX COAST WHICH
FADES AFTER 19Z.  WHILE CONVECTION SO FAR HAS BEEN COASTAL,
DAYTIME HEATING COULD ALLOW PERIPHERAL THUNDERSTORMS AHEAD OF THE
FRONT TO BECOME MORE OF A PLAYER FROM A HEAVY RAINFALL
PERSPECTIVE.  THUNDERSTORM COMPLEXES WITH THIS APPEARANCE TEND TO
LAST ANOTHER 3-4 HOURS; USED A FOUR HOUR WINDOW FOR THE MPD.  

ROTH/KREKELER

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

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

LAT...LON   30209573 29649491 29489488 29389474 28859528 
            28299647 27459722 26879751 27059817 28339833 
            29479742