MESOSCALE PRECIPITATION DISCUSSION 0354
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
751 AM EDT WED JUL 15 2015
 
AREAS AFFECTED...IN & AROUND NJ 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 151150Z - 151550Z
 
SUMMARY...A DEEP CYCLONE NEAR THE EASTERN SHORE IS EXPECTED TO
MOVE SLOWLY NORTHEASTWARD.  WITH HOURLY RAIN RATES UP TO 2.5"
POSSIBLE, FLASH FLOODING IS POSSIBLE.

DISCUSSION...A 1000 HPA LOW PRESSURE CENTER APPROACHING DELAWARE
BAY AND ITS ASSOCIATED MID-LEVEL CIRCULATION ACROSS SOUTHEAST PA
HAVE LED TO EFFICIENT RAINFALL ACROSS PORTIONS OF EASTERN PA AND
NJ THIS MORNING.  PRECIPITABLE WATER VALUES OF 1.75-2" LIE ACROSS
THE REGION PER GPS INFORMATION, 1-1.5 SIGMAS ABOVE THE NORM FOR
MID-JULY.  MUCAPES IN THE REGION ARE 500-1000 J/KG PER THE SPC
MESOANALYSIS AND RAP FORECASTS.  LOW-LEVEL INFLOW (BETWEEN 850-700
HPA) IS 20-25 KTS, NEAR THE MAGNITUDE OF THE 850-400 MEAN WIND.

WITH THIS DEGREE OF MOISTURE, HOURLY RAINFALL RATES OF 2" ARE
POSSIBLE, WHICH APPEAR TO BE REALIZED PER RECENT RADAR ESTIMATES
NEAR THE NORTHERN NJ/PA BORDER.  RECENT SATELLITE IMAGERY SHOWS A
STEADY STATE SYSTEM, WHICH SHOULD ALLOW IT TO PERSIST FOR AT LEAST
ANOTHER 3-4 HOURS.  RAP FORECASTS INDICATE MUCAPES SHOULD REMAIN
SIMILAR FOR THE NEXT FEW HOURS, BEFORE POTENTIALLY INCREASING
AROUND ITS PERIPHERY DUE TO DAYTIME HEATING.  THE MESOSCALE
GUIDANCE GENERALLY ADVERTISES LOCAL AMOUNTS OF 2-4" WHICH COULD
FALL QUICKLY CONSIDERING RAIN RATES.  THE 06Z SSEO NEIGHBORHOOD
PROBABILITIES SUGGEST THE THREAT OF EXCEEDING THREE HOUR FFGS
AHEAD OF THIS SYSTEM AND WITHIN ITS TROWAL-LIKE FEATURE INCREASE
TODAY, WITH THE BEST CHANCES OF EXCEEDANCE IN THE 16-00Z PERIOD. 
SINCE LOW-LEVEL INFLOW IS EXPECTED TO WEAKEN IN 2-3 HOURS, HAVE
PLAYED IT CAUTIOUS AND USED A FOUR HOUR WINDOW FOR THIS MPD TO SEE
HOW THE SITUATION PLAYS OUT THIS MORNING.  USED THE POSSIBLE
CATEGORY DUE TO THE SMALL AREAS OF HEAVY RAINFALL EXPECTED WITHIN
THIS REGION.

ROTH

ATTN...WFO...BGM...OKX...PHI...

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

LAT...LON   41397380 40847266 40387371 39687401 38947479 
            38937499 39207519 39347554 39947572 40667561 
            41297498