MESOSCALE PRECIPITATION DISCUSSION 0037
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
934 PM EST WED FEB 24 2016
 
AREAS AFFECTED...PORTIONS OF NJ AND SOUTHEAST NY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 250233Z - 250633Z
 
SUMMARY...A WAVY SQUALL LINE APPEARS TO BE SLOWING DOWN ACROSS THE
NORTHERN MID-ATLANTIC STATES.  AS IT IS MOVING INTO AN AREA WITH
SATURATED SOILS, FLASH FLOODING IS POSSIBLE.

DISCUSSION...A BAND OF THUNDERSTORMS WITH MESOSCALE CIRCULATIONS
IS INTERACTING WITH A MOIST AIRMASS WITH NEARLY UNIDIRECTIONAL
FLOW OUT OF THE SOUTH-SOUTHWEST AND PRECIPITABLE WATER VALUES IN
THE 1.4-1.5" RANGE PER GPS VALUES. INSTABILITY IS BEING LURED FROM
THE SOUTH INTO THE NORTHERN MID-ATLANTIC STATES AND SOUTHERN NEW
ENGLAND.  SPC MESOANALYSES INDICATE 500-1000 J/KG OF MUCAPE FROM
THE EASTERN SHORE OF THE CHESAPEAKE TO JUST OFFSHORE LONG ISLAND.  

RECENT RADAR INDICATIONS AND OBSERVATIONS ACROSS THE MID-ATLANTIC
STATES SHOW HOURLY RAIN RATES OCCASIONALLY REACHING 1-1.5", WHICH
WOULD BE MORE THAN A MATCH FOR THE LOW FLASH FLOOD GUIDANCE ACROSS
NORTHERN NEW JERSEY AND THE URBAN AREA IMMEDIATELY AROUND NEW YORK
CITY, WHICH IS AT OR UNDER 1" IN THREE HOURS.  THE CONVECTIVE BAND
AS OF LATE HAS BEEN MOVING EAST AT ~25 KTS, WITH THE ORIENTATION
OF THE OVERALL UPPER TROUGH BECOMING MORE MERIDIONAL PER SATELLITE
IMAGERY AND A RECENT BRIEFING FROM SAB/NESDIS.  THE STRONG
LOW-LEVEL INFLOW SHOULD FORCE THE CONVECTIVE LINE ALONG TO THE
NORTHEAST WITH TIME PER FORWARD PROPAGATING CONVECTIVE VECTORS.  

THE WETTER GUIDANCE APPEARS TO HAVE THE BEST HANDLE OF THIS
ACTIVITY -- NAMELY THE 00Z NAM CONEST, 12Z SPCWRF, AND 12Z
WRF4NSSL WHICH INDICATE LOCAL AMOUNTS OF 1-2" POSSIBLE, WHICH
WOULD FALL QUICKLY.  THE 18Z SSEO NEIGHBORHOOD PROBABILITIES OF
EXCEEDING THE THREE HOURLY FLASH FLOOD GUIDANCE DECLINE AFTER 06Z,
ONCE THE BAND PASSES THROUGH THE AREA MOST SUSCEPTIBLE TO HEAVY
RAIN ISSUES AND/OR DUE TO SLOWLY DECLINING PRECIPITABLE WATER AND
INSTABILITY ACROSS THE REGION AS THE CYCLONE CONTINUES LIFTS INTO
THE ST. LAWRENCE VALLEY IN CANADA.  FLASH FLOODING IS CONSIDERED
POSSIBLE, PARTICULARLY IN URBAN AREAS AND WHERE SOIL CONDITIONS
CURRENTLY RESEMBLE A BOG ACROSS PORTIONS OF THE MID-ATLANTIC
STATES.

ROTH

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

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

LAT...LON   41807295 40717335 39667442 38937531 38747564 
            38817585 41267493