MESOSCALE PRECIPITATION DISCUSSION 0158
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
936 AM EDT FRI JUL 12 2013
 
AREAS AFFECTED...EASTERN MD...DE...SOUTHEAST PA...SOUTHERN NJ 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 121336Z - 121936Z
 
SUMMARY...A CONVECTIVELY-INDUCED CIRCULATION IS EXPECTED TO MOVE
SLOWLY EAST-NORTHEAST THROUGH THE DELMARVA DURING REMAINDER OF
THIS MORNING INTO EARLY THIS AFTERNOON.  WITH A QUICK 3-5 INCHES
OF RAINFALL EXPECTED OVER AN AREA OF HIGH FLASH FLOOD GUIDANCE,
FLASH FLOODING IS POSSIBLE IN THIS REGION.

DISCUSSION...A CONVECTIVE VORTICITY MAXIMUM ACROSS THE EASTERN
SHORE/DELMARVA IS EXPECTED TO CONTINUE TRACKING SLOWLY
EAST-NORTHEAST, WHICH HAS AN ASSOCIATED SURFACE LOW ALONG A
FRONTAL ZONE.  RAINFALL RATES FROM GENERALLY ELEVATED CONVECTION
ACROSS THE REGION HAVE NOT APPRECIABLY CHANGED FROM OVERNIGHT,
WITH LOCAL AMOUNTS OF 3-5 INCHES FALLING ALONG AND NEAR ITS PATH
AS INDICATED BY RADAR AND THE DULLES AIRPORT VA OBSERVATION.  WARM
RAIN PROCESSES ARE AT PLAY HERE AS CLOUD TOPS ARE NOT COLD, WITH
RELATIVELY WARM CIRROSTRATUS SEEN ON WATER VAPOR IMAGERY WITH NO
INDICATIONS OF OVERSHOOTING TOPS NOTED.  

AS THE LOW INTERACTS WITH THE FRONTAL BOUNDARY DRAWING INFLOW OF
20-25 KNOTS WITHIN ITS NORTHERN FLANK WITHIN A REGION OF 2-2.25
INCH PRECIPITABLE WATER VALUES, PRECIPITATION SHOULD REMAIN
EFFICIENT IN THIS REGION.  DIVERGENCE ALOFT IS BEING CAUSED BY AN
UPPER LEVEL LOW DROPPING INTO WESTERN WV.  CAPE VALUES ACROSS THE
REGION ARE EXPECTED TO HOVER IN THE 1000-1500 J/KG RANGE THROUGH
THE PERIOD.  FLASH FLOOD GUIDANCE IS HIGH, ON THE ORDER OF 3-4
INCHES IN THREE HOURS.  WITH NO WEAKENING INDICATED BY RECENT RAP
RUNS TO THE SYSTEM'S ATLANTIC INFLOW INTO THIS AFTERNOON, BELIEVE
FLASH FLOODING IS POSSIBLE OVER THE NEXT SEVERAL HOURS.  A QUICK
3-5 INCHES OF RAIN COULD LEAD TO FLASH FLOODING.

ROTH

ATTN...WFO...PHI...AKQ...CTP...LWX...

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

LAT...LON   38897668 39647651 40157547 40067424 39497397 38537488
            38127597 38317645 38897668