MESOSCALE PRECIPITATION DISCUSSION 0039
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
602 PM EDT SUN APR 12 2015
 
AREAS AFFECTED...SOUTHERN LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 122150Z - 130200Z
 
SUMMARY...SLOW-MOVING INTENSE THUNDERSTORMS TO CONTINUE THROUGH
THE EARLY EVENING HOURS. WET ANTECEDENT CONDITIONS WILL FAVOR
RUNOFF PROBLEMS WITH ADDITIONAL HEAVY RAINS.

DISCUSSION...INTENSE SLOW-MOVING SHOWERS AND THUNDERSTORMS NEAR
THE SOUTHERN LA COAST ARE SLOWLY LIFT NORTH AND INLAND. THE LATEST
GOES-OTD ALGORITHM SHOWS SEVERAL OVERSHOOTING TOPS...INDICATIVE OF
INTENSE UPDRAFTS AND SUGGESTIVE OF VERY INTENSE RAINFALL RATES.

THE LAST COUPLE RUNS OF THE HRRR SEEM TO HAVE A FAIRLY DECENT
HANDLE ON THE ONGOING ACTIVITY...BUT THE HRRR SUGGESTS OVER THE
NEXT FEW HOURS THERE WILL BE A CONTINUATION OF HEAVY AND
CONCENTRATED CONVECTIVE RAINS...WITH SLOW MOVING AND BACK-BUILDING
CELLS. MODEL OUTPUT SUGGESTS LOCALIZED POTENTIAL FOR IN EXCESS OF
5 INCHES OF RAIN THROUGH 02Z...AND THIS WILL NEED TO BE CLOSELY
MONITORED. THE CONVECTION ALREADY IS TAKING ADVANTAGE OF AN
OTHERWISE VERY MOIST AND MODESTLY UNSTABLE ENVIRONMENT.
CONTRIBUTING TO SOME LARGER SCALE ASCENT IS THE PRESENCE OF A
SHORTWAVE CROSSING EASTERN TX AND SOME FAIRLY DIFFLUENT FLOW ALOFT
AS SUGGESTED BY WV/IR SAT IMAGERY.

PORTIONS OF SOUTHERN LA HAVE ALREADY SEEN HEAVY RAINFALL AMOUNTS
OVER THE LAST COUPLE OF DAYS...AND ANY ADDITIONAL HEAVY RAINS
THROUGH THIS EVENING WILL ENHANCE THE RISK OF RUNOFF PROBLEMS AND
POSSIBLY FLASH FLOODING.

ORRISON

ATTN...WFO...LCH...LIX...

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

LAT...LON   30599230 30529162 30229071 29749009 29219026 
            29239069 29289106 29539181 29669277 29759336 
            30189338 30529288