MESOSCALE PRECIPITATION DISCUSSION 0039
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT WED APR 30 2014
 
AREAS AFFECTED...ERN VA...MD...DE...SE PA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 301844Z - 302344Z
 
SUMMARY...FLASH FLOODING APPEARS LIKELY THIS AFTERNOON AS CELLS
TRAIN TO THE NNE. THIS IS ESPECIALLY TRUE NORTH OF A WARM
FRONT...INCLUDING THE CORRIDOR FROM D.C. TO BALTIMORE AND NEAR
PHILADELPHIA. BUT SOME THREAT OVERLAPS THE SEVERE WEATHER
ENVIRONMENT OUTLINED BY THE STORM PREDICTION CENTER FARHTER SOUTH.

DISCUSSION...NEAR AND WEST OF WASHINGTON D.C...LONG DURATION
RAINFALL HAD BEGUN TO PRODUCE FLASH FLOODING OWING TO INCREASING
CAPE...PW...AND ASSOCIATED RAIN RATES. CELLS WERE TRAINING...AND
SHOULD CONTINUE TO DO SO...PARTICULARLY NORTH OF THE SURFACE WARM
FRONT WHERE MEAN LAYER WINDS WILL BE THE DOMINTANT INFLUENCE ON
MOTION. LAYER STEERING WINDS WILL REMAIN PARALLEL ATOP THE WARM
ADVECTION PROFILES NEAR CLOUD BASE. SLIGHT VEERING THROUGH TIME
SHOULD PUSH THE GREATER THREAT OF REPETITIVE HEAVY RAINFALL SLOWLY
EASTWARD...WHICH IS CONSISTENT WITH RADAR TRENDS AT 1830Z.

NEAR THE WARM FRONT IN SOUTHERN VA/MD...CELLS WILL BE ROOTED
NEARER THE SURFACE AND MORE PRONE TO ISOLATION AND DEVIANT MOTION
OWING TO THE FAVORABLE SHEAR AND STRONGER COLD POOLS. STILL...THE
GREATER CAPE AVAILABLE TO THESE CELLS MAY MAXIMIZE RAIN RATES AND
YIELD FLASH FLOODING WHEREVER TRAINING OCCURS. THROUGH EARLY
EVENING THE 12Z HIRES WRF-ARW...NMM...NSSL WRF AND 16Z HRRR AGREE
AS TO AN AXIS OF MAXIMUM AMOUNTS NEAR I-95. EXPECTING 1-3 INCHES
ADDITIONAL RAIN IN 1-3 HOURS WITHIN THE HEAVIER SWATHS.

BURKE

ATTN...WFO...PHI...AKQ...CTP...LWX...RNK...

ATTN...RFC...MARFC...SERFC...

LAT...LON   40167608 39747570 39087546 38327587 37647638 37097693
            36827761 36897831 37367863 38067850 39147791 40147674
            40167608