MESOSCALE PRECIPITATION DISCUSSION 0268
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1134 PM EDT TUE AUG 12 2014
 
AREAS AFFECTED...EASTERN NJ/SOUTHEASTERN NY/LONG
ISLAND/SOUTHWESTERN CT... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 130333Z - 130803Z
 
SUMMARY...AN IMPRESSIVE AXIS OF LOW-TOPPED CONVECTION HAS PROVEN
TO PROVIDE QUITE A PUNCH UPSTREAM WITH NEARLY 8-12" OF RAINFALL IN
THE PROXIMITY OF BALTIMORE MD. THIS TORRENTIAL RAIN HAS PROGRESSED
NORTH AND EAST INTO NJ WHERE FLASH FLOODING CONTINUES TO OCCUR.
EXPECT SUCH CONDITIONS TO TRANSLATE NORTHWARD OVERNIGHT. 

DISCUSSION...RAINFALL RATES IN THE 2-3 INCH RANGE WITH LOCALLY
HIGHER AMOUNTS HAVE BEEN OBSERVED IN SOUTHEASTERN NJ DURING THE
PAST COUPLE OF HOURS. WITHIN THIS STRONGER CORES BACKBUILDING AND
TRAINING REMAINS AN ISSUE WHICH HAS LED TO NUMEROUS REPORTS OF
FLASH FLOODING...PARTICULARLY IN THE MORE URBANIZED AREAS. THE
RADAR IMAGERY/SURFACE OBSERVATIONS EVEN SHOWED A CYCLONIC
CIRCULATION WITHIN THE HEAVY RAIN BAND WITH PRESSURES RAPIDLY
FALLING. THE MOISTURE BEING ADVECTED INTO THE REGION IS QUITE
IMPRESSIVE WITH A PWAT OF 2.43" OBSERVED AT WALLOPS ISLAND AT 00Z.
THIS RANKED 99TH PERCENTILE FOR THE MIDDLE OF AUGUST.
ADDITIONALLY...LOW-LEVEL WIND PROFILES ARE QUITE FAVORABLE FOR
STORM ORGANIZATION WITH 925-850 MB WINDS IN EXCESS OF 30-35 KNOTS
BASED ON LOCAL VAD-WIND PROFILERS. IN SPITE OF INSTABILITY
REMAINING LIMITED WITH MLCAPES AROUND 500 J/KG...WARM-RAIN
PROCESSES HAVE DOMINATED AS THE WET-BULB ZERO HEIGHTS ARE UP IN
THE 14-15 KFT RANGE.

HIGH-RESOLUTION GUIDANCE VARY IN THE PLACEMENT OF THIS HEAVY
RAINFALL WITH THE 12Z HRW-ARW KEEPING MOST OF THE ACTIVITY
OFFSHORE. MEANWHILE...THE 12Z HRW-NMMB/00Z NAM CONEST/12Z SSEO
MEAN/01Z HRRR MAINTAIN IMPACTS ACROSS THE EASTERN SIDE OF NJ AND
UP INTO NYC AND WESTERN LONG ISLAND. WILL REASSESS THE SITUATION
AS ADDITIONAL 00Z MESOSCALE GUIDANCE ARRIVES.


RUBIN-OSTER

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

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

LAT...LON   40897415 41177366 41217292 40707246 40357306 40007348
            39567386 39227421 39497477 40517448 40897415