MESOSCALE PRECIPITATION DISCUSSION 0282
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 PM EDT TUE JUN 30 2015
 
AREAS AFFECTED...EASTERN PA...NORTHERN NJ...SOUTHEAST NY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 302010Z - 010110Z
 
SUMMARY...SCATTERED CONVECTION TAPPING HIGH MOISTURE CONTENT AIR
ALONG A QUASI STATIONARY BOUNDARY COULD RESULT IN FLASH FLOODING
INTO THE EARLY EVENING HOURS. 

DISCUSSION..CONVECTION CURRENTLY OVER EASTERN PA/NORTHEAST NJ
CONTINUES TO TRACK NORTHEAST NEAR AND ALONG A QUASI STATIONARY
BOUNDARY EXTENDING ACROSS EASTERN PA AND NORTHERN NJ. THE
CONVECTION IS TAPPING INCREASINGLY HIGH MOISTURE CONTENT AIR...AS
IT INTERSECTS AN AXIS OF 1.50 TO 1.75 INCH PRECIPITABLE WATER AIR
STRETCHING ACROSS THE INTERSTATE 95 CORRIDOR. KDIX RADAR INDICATED
RAINFALL RATES NEAR 1.50 INCHES AN HOUR OVER PORTIONS OF EASTERN
PA AND NORTHWEST NJ.

THE CURRENT MOTION OF THE CONVECTION ALONG THE FRONTAL BOUNDARY
TAKES IT ACROSS THE REMAINDER OF NORTHERN NJ...AS WELL AS NEARBY
SOUTHEAST NY STATE...THROUGH ABOUT 00Z. DEPENDING ON THE POSITION
OF THE FRONTAL BOUNDARY IN THE NEXT 2 OR 3 HOURS... INSTABILITY
COULD BE THE LIMITING FACTOR FOR CONVECTION TO SURVIVE INTO THE
NYC METRO AREA. IN FACT...THE LATEST HRRR AND 12Z ARW SUGGEST THAT
THE ACTIVITY WEAKENS AS IT APPROACHES THE NYC METRO AREA...WITH
THE HIGHEST RAINFALL AMOUNTS (LOCAL 2-3 INCHES) EXPECTED OVER
NORTHERN NJ AND THE LOWER HUDSON VALLEY OF NY STATE.

ONE AND THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE AS LOW AS AN
INCH OVER PORTIONS OF NORTHERN NJ...AND RAINFALL RATES COULD
EASILY EXCEED THESE VALUES. GIVEN THE UNCERTAINTY CONCERNING
WHETHER THE CONVECTION WEAKENS WITH TIME AS IT APPROACHES
NORTHEAST NJ/NYC METRO...FLASH FLOODING IS CONSIDERED POSSIBLE AT
THIS TIME.

HAYES

ATTN...WFO...ALY...BGM...BOX...OKX...PHI...

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

LAT...LON   42267397 41817271 41227307 40657369 40417396 
            40217425 40237472 40407478 40647472 40647473 
            41277487 41237482 41977472