MESOSCALE PRECIPITATION DISCUSSION 0487
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1032 AM EDT THU SEP 10 2015
 
AREAS AFFECTED...URBAN COORIDOR FROM DC TOWARD BOSTON 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 101432Z - 102032Z
 
SUMMARY...FLASH FLOODING IS LIKELY IN THE URBAN CORRIDOR FROM
WASHINGTON DC TOWARD PHILADELPHIA...NEW YORK...AND POSSIBLY BOSTON
THROUGH MID AFTERNOON.

DISCUSSION...RADAR AND SATELLITE TRENDS SHOW A STEADY INCREASE IN
THE COVERAGE AND STRENGTH OF CONVECTION ALONG BUT MOSTLY NORTH OF
THE FRONTAL BOUNDARY DRAPED ACROSS SOUTHERN NEW ENGLAND.  THE
RECENT DEVELOPMENT APPEARS TO BE IN RESPONSE TO THE APPROACH OF
TWO SHORTWAVE TROUGHS...ONE ON EACH SIDE OF THE APPALACHIANS. 
INFLUENCE FROM THESE TROUGHS IN CONJUNCTION WITH DIFFERENTIAL
HEATING IS ACCELERATING THE MOISTURE FLUX AND DESTABILIZATION IN
THE EXTREMELY MOIST AND WEAKLY CAPPED ENVIRONMENT.  

BASED ON THESE TRENDS ALONG WITH 12Z ANALYSES AND THE SIGNIFICANT
INCREASE IN THE 12Z NAM AND NAM CONUS NEST QPF...THE RECENT
INCREASE IN CONVECTIVE DEVELOPMENT SHOULD ONLY CONTINUE FROM JUST
NORTH OF THE SYNOPTIC LOW NEAR WASHINGTON DC EXTENDING NORTH AND
RUNNING PARALLEL THE FRONT TOWARD PHILADELPHIA...NEW YORK...AND
POSSIBLY BOSTON.  ANOTHER POSSIBLE LOCAL INCREASE IN FLASH
FLOODING POTENTIAL WILL BE ASSOCIATED WITH A MESOLOW EAST OF THE
NEW JERSEY SHORE...THAT SHOULD RIDE ALONG THE FRONTAL BOUNDARY
DRAPED ACROSS LONG ISLAND.  GIVEN PW VALUES IN EXCESS OF 2 INCHES
ALONG WITH AVERAGE CELL MOTIONS OF 8 TO 13 KNOTS...RAIN RATES MAY
EASILY EXCEED 2 INCHES PER HOUR...ESPECIALLY AS THE CONVECTIVE
INSTABILITY INCREASES.

JAMES

ATTN...WFO...ALY...BOX...CTP...GYX...LWX...OKX...PHI...

ATTN...RFC...MARFC...NERFC...

LAT...LON   43937049 43486960 41907086 40557341 39877478 
            39337615 39357756 39977797 40547737 40907542 
            41747338 42757204 
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