MESOSCALE PRECIPITATION DISCUSSION 0231
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 PM EDT MON SEP 02 2013
 
AREAS AFFECTED...EASTERN PA/NJ/EASTERN NY/CT/MA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 021804Z - 022204Z
 
SUMMARY...A HIGHLY UNSTABLE AND UNCAPPED THERMODYNAMIC ENVIRONMENT
WILL AID IN FURTHER CONVECTIVE DEVELOPMENT THIS AFTERNOON. THIS
MAY IMPACT AFFECTED AREAS OF PA/NJ/MA WHICH ARE CURRENTLY
EXPERIENCING VERY HEAVY RAINFALL ACCOMPANIED BY POCKETS OF FLASH
FLOODING.

DISCUSSION...THE I-95 CORRIDOR FROM THE PA/DE BORDER NORTHWARD UP
INTO COASTAL NEW ENGLAND WILL REMAIN AN AREA SUSCEPTIBLE TO FLASH
FLOODING THROUGHOUT THE AFTERNOON/EARLY EVENING. 12Z RAOBS
INDICATE THE REGION HAS WELL ABOVE NORMAL PWAT VALUES WHICH RANK
IN THE 90-95TH PERCENTILE FOR EARLY SEPTEMBER. IN SPITE OF THE
VAST CLOUD COVER...MESOSCALE MODELS SUGGEST THE ATMOSPHERE REMAINS
RATHER UNSTABLE WITH NO CAPPING EVIDENT WHICH SHOULD ALLOW
CONVECTION TO SUSTAIN ITSELF/FURTHER DEVELOP DURING THE NEXT
SEVERAL HOURS. ONE AREA OF PARTICULAR CONCERN IS SOUTHEASTERN
PA/WESTERN NJ WHICH HAS SEEN MULTIPLE HOURS OF HEAVY SHOWERS AND
THUNDERSTORMS PERSIST DROPPING SEVERAL INCHES OF RAIN. MESONET
REPORTS SUGGEST RAINFALL RATES NEAR 2 INCHES PER HOUR IN THE
VICINITY OF PHILADELPHIA PA.

AHEAD OF A WELL-DEFINED COLD FRONT MOVING ACROSS THE LOWER GREAT
LAKES...A BROAD WARM/MOIST SECTOR OVER THE UPPER
MID-ATLANTIC/LOWER INTERIOR NEW ENGLAND HAS DEVELOPED. THE VISIBLE
SATELLITE INDICATED A HIGHLY AGITATED CU FIELD WITH NUMEROUS
CONVECTIVE CELLS DEVELOPING WITHIN THE AXIS OF MAXIMUM DIURNAL
HEATING. THE GENERAL EASTWARD MOTION OF THESE STORMS WILL
EVENTUALLY CARRY THEM CLOSER TO THE I-95 CORRIDOR WHERE FFG VALUES
SHOULD SIGNIFICANTLY LOWER GIVEN THE RECENT HEAVY RAINS.
OVERALL...RECENT HIGH-RES MODELS HAVE NOT DONE WELL WITH THE
CURRENT ACTIVITY. HOWEVER...EXPECT RAINFALL RATES NEARING THE 2 TO
3 INCH RANGE PER HOUR GIVEN THE FAVORABLE MOISTURE IN PLACE
COUPLED WITH THE SLOW STORM MOTIONS.


RUBIN-OSTER

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

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

LAT...LON   39407612 40467601 41497538 42847521 42607132 41297128
            40787239 40127347 38847458 39407612