MESOSCALE PRECIPITATION DISCUSSION 0076
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1219 AM EDT WED MAR 28 2018

AREAS AFFECTED...PORTIONS OF SRN...S-CNTRL...ERN TEXAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 280418Z - 280930Z

SUMMARY...HEAVY RAINFALL IS EXPECTED TO INCREASE IN COVERAGE
ACROSS SOUTH TEXAS...SPREADING NEWD INTO PORTIONS OF CNTRL AND ERN
TEXAS OVER THE NEXT COUPLE OF HOURS. A FEW 3-5 INCH AREAS WILL BE
POSSIBLE WHICH COULD CAUSE FLASH FLOODING.

DISCUSSION...GOES EAST WATER VAPOR IMAGERY AT 04Z SHOWED A CLOSED
LOW OVER AZ/NM...MOVING EAST TOWARD TEXAS. THE RESPONSE WAS
OBSERVED IN INFRARED AND RADAR IMAGERY WITH A RAPID INCREASE IN
CONVECTION OVER SOUTH TEXAS...SOUTHWEST OF SAN ANTONIO ALONG AND
WEST OF I-35. A FEW CELLS CONTAINED LARGE HAIL...MOST NOTABLY OVER
WRN WEBB COUNTY...AND WHILE MANY CELLS WERE DISORGANIZED IN
NATURE...THEY EXHIBITED SLOW MOVEMENT WITH 0.5 TO 1.5 IN/HR RADAR
ESTIMATED RAINFALL RATES. THESE STORMS WERE OCCURRING ALONG AND
SOUTH OF AN EFFECTIVE COLD FRONT...STRETCHING FROM NERN TEXAS TO
JUST SOUTH OF SAN ANTONIO INTO THE SERRANIAS DEL BURRO IN MEXICO
AT 03Z. ESTIMATED MLCAPE VALUES SOUTH OF THE BOUNDARY OVER SOUTH
TEXAS VIA THE LATEST SPC MESOANALYSIS PAGE WERE 1000-2000 J/KG
WITH 500-1000 J/KG MUCAPE EXTENDING JUST NORTH OF THE EFFECTIVE
FRONT OVER CNTRL TEXAS.

VAD WIND DATA FROM CRP SHOWED 850 MB WINDS NEAR 35 KT FROM THE
SOUTH...AND AS THE UPPER TROUGH OVER AZ/NM CONTINUES TO SLOWLY
EDGE EAST...A COMBINATION OF THE DIURNAL CYCLE AND HEIGHT FALLS IS
EXPECTED TO ALLOW THESE LOCALLY STRONGER LOW LEVEL WINDS TO SPREAD
NORTH ACROSS THE MIDDLE TEXAS COAST INTO PORTIONS OF SERN TEXAS BY
12Z. THIS SHOULD CAUSE THE EFFECTIVE FRONTAL BOUNDARY TO LIFT
NORTH ALONG WITH INCREASING MLCAPE.

WHILE THE INITIAL CONCERN FOR TRAINING IS ONGOING ACROSS PORTIONS
OF SOUTH TEXAS...INDIVIDUAL STORM MOTIONS ARE EXPECTED TO FOLLOW
THE 0-6 KM MEAN WIND AND WITH THE INCREASING MAGNITUDE OF 850 MB
WINDS ALONG WITH SUBTLE VEERING OVER THE NEXT FEW HOURS...FLOW IS
EXPECTED TO BECOME INCREASINGLY UNIDIRECTIONAL WITH THE POTENTIAL
FOR TRAINING AS CONVECTION SPREADS EAST. DESPITE HIGH FLASH FLOOD
GUIDANCE VALUES...A QUICK 3 TO 5 INCHES MAY CAUSE FLASH FLOODING
IN A FEW LOCATIONS...ESPECIALLY IN ANY URBAN LOCATIONS ALONG I-35
OR INTO THE CLL-METRO.

OTTO

ATTN...WFO...BRO...CRP...EWX...FWD...HGX...SHV...SJT...

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

LAT...LON   32809420 32549394 32109400 31649430 30989488
            29819618 28739744 27859808 27259866 27069908
            27119954 27409998 28040022 28850029 29680039
            30259987 30499819 31269647 32339469