MESOSCALE PRECIPITATION DISCUSSION 0214...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
757 AM EDT TUE AUG 13 2013
 
AREAS AFFECTED...SOUTHEAST PA...MUCH OF NJ...SOUTHEAST
NY...SOUTHERN CT...SOUTHERN RI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 131150Z - 131750Z
 
SUMMARY...CONVECTION CONTINUES TO RAMP UP ACROSS SOUTHEAST PA AND
WESTERN NJ AT THIS TIME.  ENOUGH INSTABILITY AND LOW-LEVEL WIND
SHEAR EXISTS TO MAINTAIN ORGANIZED CONVECTION THROUGH THE DAY. 
REGIONAL FLASH FLOODING IS POSSIBLE.

DISCUSSION...THE LATEST RADAR AND SATELLITE IMAGERY SHOWS THAT
THUNDERSTORM ACTIVITY ACROSS SOUTHEAST PA AND WEST-CENTRAL NJ
CONTINUES TO BE THE UPSWING.  LATEST RAP/ARW GUIDANCE INDICATES
THAT CAPE VALUES AROUND 1000 J/KG AND LOW-LEVEL INFLOW OF 30-40
KNOTS ARE FOCUSING CONVECTION ALONG A WARM FRONT MOVING INTO THE
REGION.  CELL TRAINING FOR 2-3 HOURS IS EXPECTED AS THE AREA
PROPAGATES EAST-NORTHEAST AT 15-20 KNOTS.  THIS IS ON THE LOW OF
END OF WHAT NORMALLY FAVORS WET MACROBURST MULTICELLS AND
SUPERCELLS.  DIVERGENCE ALOFT IS BEING AIDED BY AN UPPER LEVEL
CYCLONE IN SOUTHEAST ONTARIO.  PRECIPITABLE WATER VALUES OF TWO
INCHES ARE HELPING THE PRECIPITATION EFFICIENCY, WITH RADAR
IMAGERY SUGGESTING HOURLY RAINFALL RATES OF 2-3" PER HOUR.  A
RECENT MESONET REPORT FROM WEST OF PHILADELPHIA PA INDICATES OVER
5" OF RAIN HAS FALLEN OVER THE PAST FEW HOURS, WHILE THE 11Z NSSL
QPE INDICATES THAT RAINFALL RATES OVER THE PAST FEW HOURS APPROACH
REGIONAL FLASH FLOOD GUIDANCE, CURRENTLY SITTING NEAR 3-4 INCHES
WITHIN THREE HOURS.  AS THE GUIDANCE VALUES ARE HIGH, WENT WITH
THE IDEA OF POSSIBLE REGIONAL FLASH FLOODING OVER LIKELY.  SINCE
THIS APPEARS TO BE A LONG DURATION CONVECTIVE EVENT, USED THE
MAXIMUM SIX HOURS FOR VALID TIME.

ROTH

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

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

LAT...LON   41157143 41037170 40627272 40477371 39877388 39367442
            39377512 39477661 40217735 41417452 41507187 41157143