MESOSCALE PRECIPITATION DISCUSSION 0062
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
909 PM EDT THU MAY 23 2013
 
AREAS AFFECTED...NORTHERN NJ/SOUTHEASTERN NY/WESTERN CT/WESTERN
MA... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 240109Z - 240509Z
 
SUMMARY...AN EXPANDING BATCH OF CONVECTION OCCURRING IN THE
VICINITY OF AN OUTFLOW BOUNDARY IS EXPECTED TO IMPACT REGIONS OF
SOUTHERN NEW ENGLAND EARLIER AFFECTED BY FLASH FLOODING CONDITIONS.

DISCUSSION...DURING THE PAST FEW HOURS...AN EVOLVING LINE OF
CONVECTION WAS SEEN TRACKING EASTWARD THROUGH CENTRAL PA/NY WITH
CONSIDERABLE GROWTH OCCURRING DOWNSTREAM. CLOUD TOPS HAVE COOLED
CONSIDERABLY DURING THE PAST HOUR AS THE ONCE NARROW BAND OF
CONVECTION HAS TRANSITIONED OVER TO A WIDER SWATH OF HEAVY
RAINFALL. AFFECTED AREAS DOWNSTREAM ACROSS SECTIONS OF NORTHERN
NJ/SOUTHEASTERN NY HAVE SEEN UPWARDS OF 2 TO 3 INCHES OF RAINFALL
THE PAST 6 HOURS. FURTHER...PWAT VALUES OVER THIS REGION ARE
APPROACHING THE 99TH PERCENTILE FOR LATE MAY WITH THE 00Z RAOB AT
OKX SUPPORTING A VALUE OF 1.67 INCHES. THUS...ABUNDANT
TROPOSPHERIC MOISTURE REMAINS IN PLACE FOR ADDITIONAL HEAVY
RAINFALL. 

HIGH-RES MODELS HAVE NOT HANDLED THE CONVECTION VERY WELL
THROUGHOUT THE AFTERNOON AND EVENING HOURS. HOWEVER...A MAJORITY
OF THE GUIDANCE HAS SUPPORTED LOCALLY HEAVY RAINFALL SOMEWHERE
ACROSS COASTAL NEW ENGLAND INTO THE OVERNIGHT HOURS. THIS ACTIVITY
IS EXPECTED TO BE RATHER PROGRESSIVE IN NATURE AS THE 500-MB TROF
CONTINUES TO NOSE EASTWARD ACROSS THE GREAT LAKES REGION. AN
ADDITIONAL 1 TO 2 INCHES OF RAINFALL WILL BE POSSIBLE IN THE
AFFECTED REGION THROUGH 05Z. 


RUBIN-OSTER


ATTN...WFO...BOX...OKX...ALY...PHI...

LAT...LON   40857500 41407452 41857399 42477342 42577297 42347259
            42017254 41717277 41327321 40917361 40467409 40317431
            40467478 40857500