MESOSCALE PRECIPITATION DISCUSSION 0040
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
627 PM EDT WED APR 30 2014
 
AREAS AFFECTED...ERN PA...SRN NY...WRN CT...NRN DE 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 302158Z - 010228Z
 
SUMMARY...RAIN RATES WILL INCREASE AS RICH LOW LEVEL AIR ARRIVES
FROM THE SOUTH. PARTS OF THE REGION WERE ALREADY EXPERIENCING
AREAL INUNDATION FLOODING AT 2130Z...AND INSTANCES OF MORE RAPID
SURFACE RUNOFF/FLASH FLOODING MAY OCCUR THIS EVENING.

DISCUSSION...WHAT BEGAN AS A LONG DURATION FLOOD EVENT MAY
TRANSITION TOWARD FLASH FLOODING LOCALLY. IN THE MIDST OF ONGOING
RAIN...RAP SOUNDINGS FORECAST AN INCREASE OF LOW LEVEL TEMPERATURE
AND MIXING RATIOS AT THE SAME TIME THAT BROAD SCALE MID LEVEL LIFT
SUSTAINS LAPSE RATES SUPPORTIVE OF CONVECTION. ECHOES HAD GAINED
INTENSITY NEAR PHILADELPHIA BY LATE AFTERNOON...WITH RADAR AND
RAIN GAUGES INDICATING RATES APPROACHING 1 INCH PER HOUR. THIS
ENVIRONMENT WILL BE SWEPT NORTHWARD AHEAD OF A SUBTLE MID LEVEL
TROUGH EVIDENT IN WATER VAPOR IMAGERY AND RAP PLAN VIEW 700 MB
FORECASTS.

GIVEN THE SUPPORTIVE MID LEVEL ASCENT AND RELATIVE INDEPENDENCE OF
THIS EVENT ON THE NEAR-SURFACE LAYER...SUSPECT THAT SOME WESTWARD
EXPANSION OF HEAVY RAINFALL IS ALSO POSSIBLE AS ALREADY EVIDENCED
ACROSS VA/MD. FLASH FLOOD GUIDANCE VALUES IN PARTS OF THIS REGION
ARE CHARACTERIZED BY ONE INCH OR LESS IN AN HOUR OR 1.5 OR LESS IN
3 HOURS...SUGGESTING FLASH FLOODING WILL BE POSSIBLE BENEATH THE
HEAVIER EMBEDDED CONVECTION.

BURKE

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

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

LAT...LON   39697416 39367497 39657583 40087648 40797618 41427555
            41837488 42027352 41417262 40657283 39697416