MESOSCALE PRECIPITATION DISCUSSION 0492
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT FRI SEP 11 2015
 
AREAS AFFECTED...SOUTH TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 111818Z - 120000Z
 
SUMMARY...HEAVY RAIN WILL EXPAND SOUTHWARD INTO PORTIONS OF SOUTH
TEXAS THROUGH 00Z. FLASH FLOODING CONCERNS WILL LIKELY VARY
DEPENDING ON LOCATION...BUT LOCALLY VERY HEAVY RAINFALL IS
EXPECTED.

DISCUSSION...AT 18Z...VISIBLE SATELLITE/SURFACE OBSERVATIONS
PLACED A SWD SAGGING OUTFLOW BOUNDARY ACROSS THE WRN GULF
COAST...JUST NORTH OF RKP. DUAL-POL RADAR ESTIMATES FROM CRP
INDICATED RAIN RATES BETWEEN 2-3 IN/HR ACROSS PORTIONS OF REFUGIO
AND ARANSAS COUNTIES AMID A VERY MOIST AIRMASS CHARACTERIZED BY
DEWPOINTS IN THE MID TO UPPER 70S. MOSTLY CLEAR SKIES ON VISIBLE
IMAGERY THIS MORNING HAVE CERTAINLY NOT REDUCED SIGNIFICANT
INSTABILITY NOTED ON 12Z RAOBS FROM BRO AND CRP. VISIBLE IMAGERY
ALSO SHOWED SOUTH-NORTH CLOUD STREETS ALONG THE SOUTH TEXAS
PRAIRIES INDICATIVE OF THE MOIST LOW LEVEL FLOW INTERSECTING THE
WRN PORTION OF THE OUTFLOW BOUNDARY ALONG WITH NEW CELLS
DEVELOPING ACROSS INLAND PORTIONS OF SOUTH TEXAS.

WHILE UPPER DIFFLUENCE OVER THE REGION IS FORECAST TO DIMINISH AS
THE BASE OF A LARGE SCALE UPPER TROUGH AXIS OVER OKLAHOMA/NORTH
TEXAS DRAWS NEARER...AMPLE MOISTURE/INSTABILITY IS FORECAST TO
FUEL ADDITIONAL CONVECTION THROUGH THE REMAINDER OF THE AFTERNOON
OVER SOUTH TEXAS WITH RAINFALL RATES BETWEEN 2-3 IN/HR. THE BEST
FOCUS FOR HEAVY RAIN MAY BE NEAR THE COAST AS THE WRN PORTION OF
THE OUTFLOW BOUNDARY INTERACTS WITH SEA BREEZE CONVERGENCE AND ELY
LOW LEVEL FLOW FORECAST TO DEVELOP INTO THE EVENING HOURS AS THE
BOUNDARY SAGS FARTHER SOUTH. 

THE 12Z HI-RES MODELS ARE UNANIMOUS IN A SIGNAL FOR HEAVY RAIN
WITH AMOUNTS ACROSS A FEW LOCATIONS RANGING FROM 3-6 INCHES.
DESPITE POOR ORGANIZATION OF INDIVIDUAL CELLS...THIS DOES NOT SEEM
UNREASONABLE GIVEN THE VERY HIGH MOISTURE CONTENT IN PLACE.

OTTO

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

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

LAT...LON   29059908 28919806 28879676 28739627 28399613 
            28099639 27259674 25859678 25789764 26219853 
            27099954 27980034 28570018