MESOSCALE PRECIPITATION DISCUSSION 0491
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
822 AM EDT FRI SEP 11 2015
 
AREAS AFFECTED...LOCATIONS ALONG THE W-CNTRL TO CNTRL GULF COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 111221Z - 111800Z
 
SUMMARY...LOCALLY HEAVY RAIN WITHIN A VERY MOIST ENVIRONMENT WILL
LIKELY CONTINUE OVER THE NEXT SEVERAL HOURS...WITHIN ROUGHLY 50
MILES OF THE GULF COAST...BEFORE POSSIBLY MOVING OFFSHORE BY 18Z.
POTENTIAL EXISTS FOR SOME LOCATIONS TO PICK UP 3-6 INCHES WHICH
MAY CAUSE FLASH FLOODING IN A FEW LOCATIONS.

DISCUSSION...REGIONAL RADAR IMAGERY AT 12Z SHOWED TWO MAIN
CLUSTERS OF SHOWERS/THUNDERSTORMS OCCURRING...ONE OVER THE
MID-UPPER TEXAS COAST AND THE OTHER OVER SERN LOUISIANA. THESE
CLUSTERS OF HEAVY RAIN WERE OCCURRING NEAR AND AHEAD OF A 700 MB
FRONT/TROUGH AXIS BENEATH A WIDELY DIFFLUENT UPPER FLOW PATTERN.
THE ENVIRONMENT WAS CHARACTERIZED BY PRECIPITABLE WATER VALUES
BETWEEN 2.0 AND 2.4 INCHES PER RECENT GPS SITE MEASUREMENTS...WITH
DUAL-POL ESTIMATED RAIN RATES OF 1-2 IN/HR.

THE 700 MB TROUGH AXIS SHOULD SINK SOUTH OVER THE NEXT FEW
HOURS...BUT HEAVY RAIN IS EXPECTED TO FILL INTO SWRN
LOUISIANA...BETWEEN THE TWO ONGOING CLUSTERS SHORTLY. INDIVIDUAL
CELLS MOVING OFF TO THE EAST AT GENERALLY 15 KTS SHOULD BE
ACCOMPANIED BY 850 MB INFLOW RANGING BETWEEN 15 - 25 KTS FROM THE
WSW...WITH THE HIGHER END OF THAT RANGE FORECAST TO LINGER OVER
ERN PORTIONS OF THE MPD THREAT AREA INTO THE VERY EARLY AFTERNOON.
THESE WINDS SHOULD CONTINUE TO ALLOW REPEATING CELL MOTIONS AND
THE POTENTIAL FOR RAINFALL TOTALS TO MEET OR EXCEED FLASH FLOOD
GUIDANCE OF 2.5 TO 3 INCHES IN 3 HOURS...WITH 6 HOUR RAINFALL
TOTALS UP TO 6 INCHES POSSIBLE...DESPITE RATHER POOR ORGANIZATION
OF INDIVIDUAL STORM CELLS.

OTTO

ATTN...WFO...HGX...LCH...LIX...MOB...

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

LAT...LON   30868836 30198798 29548889 29099061 29319349 
            28539588 29219642 30159547 30499454 30669305 
            30789047