MESOSCALE PRECIPITATION DISCUSSION 0369
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
638 PM EDT TUE JUN 21 2016
 
AREAS AFFECTED...MD, DE, AND NORTHERN VA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 212237Z - 220437Z
 
SUMMARY...NEW THUNDERSTORM ACTIVITY ACROSS THE REGION IS
PROLONGING THE HEAVY RAIN THREAT.  FLASH FLOODING REMAINS POSSIBLE
OVER THE NEXT SEVERAL HOURS.

DISCUSSION...SATELLITE AND RADAR IMAGERY HAS SHOWN AN UPTICK IN
CONVECTIVE DEVELOPMENT AND COVERAGE ACROSS PORTIONS OF MD AND
NORTHERN VA, JUST AHEAD OF A SHORTWAVE MOVING INTO NORTHWEST PA. 
A FEW OVERSHOOTING TOPS WERE NOTED ON THE MOST RECENT VISIBLE
SATELLITE IMAGE.  A WAVE OF LOW PRESSURE REMAINS NEAR THE MD/WV/PA
BORDER JUNCTION WHICH HAS LED TO A CONTINUATION OF THE WARM AIR
ADVECTION PATTERN NEAR AN OUTFLOW BOUNDARY FROM PREVIOUS
CONVECTION EXTENDING THROUGH EASTERN WV INTO NORTHERN VA. 
PRECIPITABLE WATER VALUES ARE 1.6-1.9" PER GPS DATA.  INFLOW AT
850 HPA REMAINS CONVERGENT OUT OF THE WEST-SOUTHWEST AT 20-30 KTS
AND ORTHOGONAL INTO THE BOUNDARY, IMPORTING 1500-2500 MLCAPES INTO
THE REGION.

THE MESOSCALE/CAM GUIDANCE IS BEGINNING TO STRUGGLE IN THIS
REGION, AS IT WAS FORECASTING THE EARLIER CONVECTIVE AREA TO SWEEP
OUT AS A CONVECTIVE ARC INTO EASTERN VA.  EVEN SO, THEIR SIGNAL
FOR HEAVY RAINFALL DID NOT DIMINISH UNTIL ~ 05Z.  RECENT RAP
FORECASTS INDICATE LITTLE MOVEMENT TO THE BOUNDARY CURRENTLY
ACROSS NORTHERN VA THROUGH 06Z.  THE AVAILABLE INSTABILITY/MLCAPES
IN VA IMPLY ANOTHER 4-6 HOURS OF ISSUES IS POSSIBLE, SO TO PLAY IT
SAFE, USED A SIX HOUR HORIZON.  CONVECTION SHOULD CONTINUE TO MOVE
ROUGHLY EAST-SOUTHEAST TOWARDS 40 KTS.  HOURLY RAIN RATES IN
LONGER TRAINING BANDS COULD RETURN TO 1.5-2.5", WHICH WOULD CAUSE
ISSUES IN URBAN AREAS AND SATURATING SOILS.  ADDITIONAL LOCAL
AMOUNTS OF 2-4" ARE CONSIDERED POSSIBLE ACROSS THE REGION, WHICH
IS ADVERTISED BY THE GUIDANCE NEAR (BUT SOUTH OF) THIS AREA.

ROTH

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

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

LAT...LON   39887763 39597638 38937526 38387500 37677532 
            37137587 38257735 39607817