MESOSCALE PRECIPITATION DISCUSSION 0057
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
125 AM EST FRI MAR 02 2018

AREAS AFFECTED...NORTHERN NJ, LONG ISLAND, & SOUTHERN NEW ENGLAND

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 020624Z - 021224Z

SUMMARY...FRONTOGENESIS/STRENGTHENING INFLOW NORTH OF A LOW
PRESSURE AREA OFFSHORE NJ SHOULD LEAD TO HEAVY RAIN.  LOCAL
AMOUNTS UP TO 2" ARE POSSIBLE WHICH CAN BE PROBLEMATIC IN URBAN
AREAS.

DISCUSSION...A COMPLEX SURFACE PATTERN IS SEEN ACROSS THE NORTHERN
MID ATLANTIC AT THIS TIME, WITH LOW PRESSURE AREAS IN NORTHWEST
PA, NEAR CHESAPEAKE BAY, AND OFFSHORE NJ.  PRECIPITABLE WATER
VALUES OF 0.75-1" LIE ACROSS SOUTHERN NEW ENGLAND AND LONG ISLAND
PER GPS VALUES.  INFLOW AT 850 HPA IS INCREASING INTO THE REGION,
UP TO 45 KTS PER THE UPTON NY VAD WIND PROFILE.  MU CAPE VALUES
SOUTH OF THE AREA ARE ~100 J/KG ACROSS CHESAPEAKE BAY AND OFFSHORE
SOUTHERN NJ PER SPC MESOANALYSES.  HOURLY RAIN TOTALS ACROSS
CENTRAL AND SOUTHERN NJ AND POINTS WITHIN LONG ISLAND HAVE
RECENTLY APPROACHED 0.30" PER MESONET OBSERVATIONS, A FEW HOURS
AHEAD OF WHAT THE 00Z HREF PROBABILITIES OF REACHING 0.25"
SUGGESTED.

THE MESOSCALE GUIDANCE SHOWS HOURLY RAIN TOTALS INCREASING FROM
HERE ON OUT, WITH TOTALS EXCEEDING 0.5" AS SOON AS 09Z PER 00Z
HREF PROBABILITIES.  IT IS AT THIS TIME WHEN FRONTOGENESIS AT 650,
750, AND 850 HPA BEGINS TO ALIGN ACROSS THE AREA AND STRENGTHEN
PER 18-00Z GFS FORECASTS DUE TO THE STRENGTHENING SURFACE LOW
OFFSHORE.  WHILE RULES OF THUMB BASED ON AVAILABLE MOISTURE AND
INSTABILITY SUGGEST THAT HOURLY RAIN TOTALS SHOULD MAXIMIZE NEAR
0.50" LOCALLY, THE DEGREE OF 850 HPA INFLOW (60-65 KTS) BY 12Z
COULD ALLOW FOR HOURLY TOTALS TO RISE TO 1" LOCALLY BY THE END OF
THE MPD PERIOD.  THE MESOSCALE GUIDANCE HAS A SIGNAL FOR LOCAL
AMOUNTS TO 2" THROUGH 12Z.  AS A GOOD AMOUNT OF THIS AREA IS
URBANIZED AND/OR RECEIVED ABOVE NORMAL OVER THE PAST COUPLE WEEKS,
FLOODING IS A POSSIBILITY IN AREAS OF POOR DRAINAGE.

ROTH

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

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

LAT...LON   42086993 41376983 41187009 41227091 41017174
            40697270 40457372 40227392 40227406 40387453
            40937467 41567326 42077109