MESOSCALE PRECIPITATION DISCUSSION 0186
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
951 AM EDT TUE JUN 09 2015
 
AREAS AFFECTED...CENTRAL GULF COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 091350Z - 091650Z
 
SUMMARY...A CONVECTIVE CLUSTER IS BROADENING AS IT APPROACHES THE
GULF COAST.  RAINFALL RATES UP TO 2.5" AN HOUR COULD LEAD TO FLASH
FLOODING.

DISCUSSION...SATELLITE AND RADAR IMAGERY REVEAL A BROADENING
CONVECTIVE CLUSTER WHICH HAS BEEN MOVING STEADILY TO THE SOUTH AT
20-25 KTS TOWARDS THE GULF COAST.  IT LIES NEAR THE TAIL END OF AN
UPPER TROUGH WHICH IS BEING REINFORCED BY RIDGING ALOFT ASSOCIATED
WITH BLANCA'S REMAINS IN THE SOUTHWEST.  PRECIPITABLE WATER VALUES
IN THE AREA ARE JUST ABOVE 2".  WHILE LOW-LEVEL INFLOW IS WEAK --
10 KTS -- ITS 20 KT PROGRESSION IS LEADING TO SUFFICIENT LOW-LEVEL
INFLOW FOR THE CLUSTER'S MAINTENANCE AND RECENT EXPANSION, LIKELY
DOUBLE THE MAGNITUDE OF THE MEAN 850-400 HPA WIND.  MUCAPE VALUES
OF 1000-2000 J/KG INHABIT THE REGION.

THE CONCERN IS THAT ACTIVITY COULD TRY TO HANG UP ACROSS SOUTHEAST
LA WHERE COLDER CLOUD TOPS ARE PRESENT AND LESSER FORWARD
PROGRESSION HAS BEEN NOTED.  WHILE FLASH FLOOD GUIDANCE VALUES ARE
HIGH, URBAN AREAS ARE EASILY PRONE TO FLASH FLOODING WITH HOURLY
RAIN RATES UP TO 2.5", WHICH HAVE BEEN IMPLIED VIA RADAR
ESTIMATES.  THERE IS A SIGNAL IN THE MESOSCALE GUIDANCE FOR 3-4"
OF RAINFALL TO FALL OVER THE NEXT SEVERAL HOURS.  FLASH FLOODING
IS CONSIDERED POSSIBLE IN THIS REGION.  USED A THREE HOUR WINDOW
DUE TO THE UNCERTAINTY REGARDING THE CONVECTIVE AREA'S POSSIBLE
PERSISTENCE -- A SLOWER PROGRESSION COULD LEAD TO LESS
ORGANIZATION.

ROTH

ATTN...WFO...JAN...LCH...LIX...MOB...

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

LAT...LON   31268814 31168801 31138773 30858742 30368718 
            30188769 30158837 30188876 29868876 29678881 
            29488942 29589043 29749116 29999156 30429159 
            30799143 31029036 31168907