MESOSCALE PRECIPITATION DISCUSSION 0510
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
633 PM EDT SUN JUL 31 2016
 
AREAS AFFECTED...NERN MD/NRN DELMARVA PENINSULA INTO ERN PA/NJ AND
NYC METRO 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 312230Z - 010400Z
 
SUMMARY...THE POTENTIAL FOR A FEW LOCALIZED...VERY HEAVY RAINFALL
TOTALS IS EXPECTED TO DEVELOP ACROSS PORTIONS OF THE NRN
MID-ATLANTIC REGION INTO SRN NEW YORK STATE IN THE 00-03Z TIME
FRAME. RAINFALL RATES OF 2+ IN/HR WITH NEAR STATIONARY MOVEMENT OF
CELLS COULD LEAD TO FLASH FLOODING ESPECIALLY ACROSS WET
ANTECEDENT CONDITIONS. COVERAGE AND EXACT LOCATION IS UNCERTAIN.

DISCUSSION...22Z SURFACE ANALYSIS PLACED A WELL DEFINED STATIONARY
FRONT NWWD THROUGH SRN NJ INTO WEAK LOW PRESSURE IN E-CNTRL
PA...WITH THE FRONT EXTENDING WEST INTO ERN OH. A FEW THUNDERSTORM
OUTFLOWS WERE ALSO NOTED TO BE SAGGING SWWD ACROSS SERN PA AND SRN
NJ VIA KDIX RADAR REFLECTIVITY. CLOUD COVER NORTH OF THE FRONT HAS
LIMITED THE AMOUNT OF INSTABILITY ACROSS SRN NY/NRN NJ/NERN
PA...BUT WEAK WLY FLOW OVERRUNNING THE DIABATICALLY ENHANCED
BOUNDARY HAS ALLOWED FOR WEAK BUT SLOW MOVING CONVECTION OVER THE
LAST SEVERAL HOURS ACROSS PORTIONS OF NERN PA AND PORTIONS OF NJ.
RECENT GPS MEASUREMENTS INDICATED PRECIPITABLE WATER VALUES OF
ROUGHLY 1.8 TO 1.9 INCHES FROM NERN MD TO LONG ISLAND...INDICATIVE
OF A VERY MOIST AIRMASS.

WATER VAPOR IMAGERY SHOWED A MID-UPPER LEVEL TROUGH AXIS OVER
WV...MOVING EWD...WITH FORCING OUT AHEAD OF THE TROUGH EXPECTED TO
REACH ERN PA BETWEEN 00-03Z. WHILE RAP WINDS AT 850 MB HAVE BEEN
ABOUT 5-10 KTS TOO WEAK COMPARED TO VAD WIND PLOTS AT KDOX AND
KPHL...THE RAP SHOWS SLIGHTLY STRONGER 850-700 MB FLOW IMPACTING
THE STATIONARY FRONT AND REMNANT OUTFLOW BOUNDARIES ACROSS THE NRN
DELMARVA PENINSULA AND SRN NJ WHICH COULD ALLOW FOR SOME NEARLY
STATIONARY MOVEMENT OF THUNDERSTORMS GIVEN KINEMATIC PROFILES.

FARTHER NORTH...BETTER SYNOPTIC LIFT IS PRESENT WITH THE RIGHT
ENTRANCE REGION OF A 70-90 KT UPPER LEVEL JET OVER NRN NJ INTO THE
NYC METRO REGION...BUT A LACK OF INSTABILITY IS LIKELY TO LIMIT
RAINFALL RATES. RECENT RUNS OF THE HRRR/HRRR_P HAVE SHOWN TOO MUCH
INSTABILITY NORTH OF THE STATIONARY FRONT AND ARE POSSIBLY TOO
HEAVY PRIOR TO 06Z.

WHILE THE POTENTIAL FOR ISOLATED RAINFALL RATES OF 2+ IN/HR WITHIN
NEARLY STATIONARY CELLS IS PRESENT...THE COVERAGE REMAINS
UNCERTAIN...BUT IT APPEARS THE FORCING WILL INCREASE IN THE 00-03Z
TIME FRAME.

OTTO

ATTN...WFO...BGM...CTP...OKX...PHI...

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

LAT...LON   41607477 41507431 41277397 40647374 39917382 
            39097447 39207549 39577599 40277653 41077629 
            41597541