MESOSCALE PRECIPITATION DISCUSSION 0912
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1024 PM EDT TUE OCT 24 2017

AREAS AFFECTED...LONG ISLAND...CT...RI...MA...SOUTHEAST
VT...CENTRAL/SOUTHERN NH

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 250220Z - 250630Z

SUMMARY...BANDS OF HEAVY RAIN WILL CONTINUE TO LIFT UP ACROSS
CENTRAL/SOUTHERN NEW ENGLAND OVER THE NEXT FEW HOURS...WITH
ADDITIONAL FLASH FLOODING EXPECTED.

DISCUSSION...VERY MOIST DEEP LAYER SOUTHERLY FLOW CONTINUES TO
ADVANCE UP ACROSS SOUTHERN NEW ENGLAND THIS EVENING AND RADAR
IMAGERY IS SHOWING MULTIPLE BANDS OF HEAVY SHOWERS TENDING TO
TRAIN OVER THE SAME AREA. RECENT DUAL-POL RADAR DATA IS INDICATING
RAINFALL RATES OF OVER 2 INCHES/HR DOWN ACROSS PARTS OF CENTRAL CT
AND ALREADY THERE ARE STORM TOTALS AMOUNTS OF 3 TO 4 INCHES.

THE HEAVY RAINFALL RATES ARE BEING FACILITATED BY A NOSE OF PWATS
OF 1.7 TO 1.9 INCHES...AND THE AXIS OF DEEP MOISTURE EXTENDS WELL
SOUTH DOWN OFF THE EAST COAST AND TOWARD SOUTH FL...WITH
EFFECTIVELY AN ATMOSPHERIC RIVER SET-UP. THE HEAVY RAINFALL IS
BEING FACILITATED THE GRADUAL EASTWARD ADVANCE OF A DEEP LAYER
TROUGH OVER THE GREAT LAKES AND OH VALLEY AND PROXIMITY OF A
QUASI-STATIONARY FRONT FROM JUST EAST OF THE DELMARVA AND
EXTENDING NORTH UP COASTAL AREAS OF NJ AND INTO FAR EASTERN NY.

THE LATEST NON-OPERATIONAL GOES-16 10.3 MICRON/IR IMAGERY SHOWS
MULTIPLE CLUSTERS OF CONVECTION ALIGNED N/S JUST AHEAD OF THE
FRONT AND ALSO SOUTH OF LONG ISLAND AND SOUTHERN NEW ENGLAND. SOME
OF THIS CONVECTION IS EXPECTED TO CONTINUE TO LIFT NORTHWARD AND
INLAND OFF THE ATLANTIC OCEAN. THE CONVECTION OFFSHORE IS BEING
AIDED BY RELATIVELY DIFFLUENT FLOW ALOFT AND A MODEST INSTABILITY
GRADIENT WITH MLCAPE VALUES OF 500 TO 1000 J/KG...ALTHOUGH THIS
DROPS OFF MARKEDLY FARTHER NORTH OVER INTERIOR NEW ENGLAND.

EXPECT ADDITIONAL RAINFALL AMOUNTS OF AS MUCH AS 2 TO 4 INCHES
THROUGH 06Z...AND THIS WILL LIKELY PROMOTE ADDITIONAL FLASH
FLOODING CONCERNS GOING PAST MIDNIGHT AS A RESULT.

ORRISON

ATTN...WFO...ALY...BOX...BTV...GYX...OKX...

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

LAT...LON   44127141 43857105 42867118 41987140 41217168
            40817214 40637312 41237320 41867312 42707285
            43847225