MESOSCALE PRECIPITATION DISCUSSION 0516
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
223 PM EDT MON AUG 01 2016
 
AREAS AFFECTED...EASTERN PA...NJ...NORTHEAST MD...DE 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 011830Z - 012330Z
 
SUMMARY...CONVECTION DEVELOPING OVER PORTIONS OF THE NORTHERN MID
ATLANTIC COULD PRODUCE HOURLY RAINFALL RATES NEAR 2.00
INCHES...WHICH COULD RESULT IN FLASH FLOODING THIS
AFTERNOON...ESPECIALLY IN AREAS WITH LOWER FLASH FLOOD GUIDANCE
VALUES. 

DISCUSSION...WIDELY SCATTERED CONVECTION IS BEGINNING TO DEVELOP
ACROSS PORTIONS OF SOUTHEAST PA...NORTHEAST MD...SOUTHERN NJ AND
DE EARLY THIS AFTERNOON. THE CONVECTION IS DEVELOPING IN AN AREA
OF 1000-15000 J/KG MLCAPE...WHERE THE CLOUD COVER HAS BEEN THE
THINNEST THROUGH THE MORNING HOURS. THE CONVECTION IS ALSO
DEVELOPING ON A PRECIPITABLE WATER GRADIENT NORTH OF THE SURFACE
FRONT... WHICH VALUES RANGING BETWEEN 1.75 AND 2.00 INCHES. THUS
FAR...BOTH KDIX AND KDOX RADARS HAVE INDICATED HOURLY RAINFALL
RATES BETWEEN 1.50 AND 1.75 INCHES. WHILE THERE COULD BE SOME HAIL
CONTAMINATION (AS SUGGESTED BY THE KDOX HCA PRODUCT AND DRY AIR IN
THE MID LEVELS PER RAP SOUNDINGS)  HIGH WET BULB ZERO VALUES AND
DEEP WARM CLOUD LAYERS WOULD INDICATE EFFICIENT RAINFALL PRODUCERS.

THE LATEST RAP SUGGESTS THAT INSTABILITY REMAINS HIGHEST ACROSS
SOUTHEAST PA... SOUTHERN NJ/NORTHEAST MD AND DE THROUGH 23Z...AS
THE AIRMASS NORTH OF THIS AREA BECOME MORE STABLE WITH TIME.
SYNOPTIC SCALE ASCENT IS PROVIDED BY THE RIGHT REAR QUADRANT OF A
75 KNOT JET CROSSING SOUTHERN AND CENTRAL NEW ENGLAND...BUT THE
WANING INSTABILITY COULD LIMIT THE CONVECTIVE COVERAGE...SO THE
EXTENT OF THE OVERALL FLASH FLOOD THREAT IS SOMEWHAT UNCERTAIN. 

ONE HOUR FLASH FLOOD VALUES ARE AS LOW AS AN INCH OVER PORTIONS OF
CENTRAL NJ... SOUTHEAST PA...NORTHERN MD AND NORTHERN DE (DUE TO
RECENT HEAVY RAIN EPISODES). EVEN SCATTERED CONVECTION IN THIS
MOIST AIRMASS IS CAPABLE OF PRODUCING RAINFALL RATES NEAR 2.00
INCHES...WHICH WOULD BE MORE THAN SUFFICIENT TO PRODUCE FLASH
FLOODING IN AREAS WITH LOW FLASH FLOOD GUIDANCE.

HAYES

ATTN...WFO...AKQ...BGM...CTP...LWX...OKX...PHI...

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

LAT...LON   41607523 41387447 41007392 39887376 39247411 
            38857458 38477569 38927701 39997794 40527751 
            41287617