MESOSCALE PRECIPITATION DISCUSSION 0041
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
827 AM EDT TUE APR 14 2015
 
AREAS AFFECTED...SRN LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 141226Z - 141826Z
 
SUMMARY...THUNDERSTORMS WITH HEAVY RAIN WILL INCREASE IN
ORGANIZATION AND COVERAGE THIS MORNING. LOCAL AMOUNTS OF 2 TO 3
INCHES IN 2 TO 3 HOURS ARE LIKELY. THIS MAY PRODUCE FLASH
FLOODING...ESPECIALLY SOUTH OF INTERSTATE 10 WHERE RAINFALL WAS 2
TO 4 INCHES ABOVE NORMAL OVER THE PAST WEEK. 

DISCUSSION...AT 12Z HEAVY RAINFALL WAS EXPANDING IN COVERAGE ALONG
A ZONE OF LOW LEVEL CONVERGENCE AND LIFT ASSOCIATED WITH THE
ENTRANCE REGION OF A DEVELOPING 250 MB JET STREAK. CONVECTION WAS
ROOTED ALOFT...BUT MAY BECOME INCREASINGLY NEAR-SFC BASED AS
MODEST INSOLATION OCCURS AND LOW LEVEL INFLOW INCREASES PER RAP
FORECASTS. CONVECTION SOUTH OF LAFAYETTE WAS ALREADY TAKING ON A
BROADER...MORE ORGANIZED APPEARANCE. AN MCS OFFSHORE COULD BE A
FACTOR IN HOW THINGS EVOLVE...BUT WITH ONLY WEAK OUTFLOWS
GENERATED IN A HIGH PW ENVIRONMENT...ANY MID LEVEL CIRCULATION
OFFSHORE WOULD STEER TOWARD SE LA...AND MAY ENHANCE LIFT BY
MIDDAY. THIS SIGNAL SEEMS TO APPEAR IN THE GLOBAL MODELS...GFS 600
MB...AND HIGH RESOLUTION MODELS...WRF-ARW SIMULATED REFLECTIVITY.

THE WRF-ARW AND NMM WERE BEST HANDLING THE EARLY MORNING
CONVECTION. PLACEMENT OF THEIR QPF FITS WELL WITH THE PAST TWO
12Z/00Z RUNS OF THE SSEO MEAN. THE 09Z HRRR WAS SLOWER...BUT
EVENTUALLY FILLED IN SRN/SE LA WITH WIDESPREAD 1-3 INCH RAINFALL.
THE VARIOUS METHODS OF PREDICTED MOTION FOR BOTH CELLS AND
CONVECTIVE SYSTEMS EITHER YIELD SLOW 10 KNOT MOTION OR SMALL
CROSSING ANGLES BETWEEN INDIVIDUAL CELLS AND COLD POOL DRIVEN
SEGMENTS...SUGGESTING TRAINING. ISOLATED RAINFALL ABOVE 3 INCHES
AND ASSOCIATED FLASH FLOODING IS POSSIBLE THROUGH 18Z...WITH THE
GREATEST THREAT SLOWLY MIGRATING FROM WEST TO EAST. 

BURKE

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

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

LAT...LON   30869129 30508967 30098897 29438918 28569019 
            28629235 29099330 29689348 30439273