MESOSCALE PRECIPITATION DISCUSSION 0784
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
620 PM EDT TUE SEP 05 2017

AREAS AFFECTED...NRN NJ/SRN NY INTO CNTRL/SRN NEW ENGLAND

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

VALID 052219Z - 060320Z

SUMMARY...SCATTERED LOCATIONS OF FLASH FLOODING WILL BE POSSIBLE
OVER THE NEXT 3-5 HOURS FROM NRN NJ/SRN NY INTO SRN/CNTRL NEW
ENGLAND. 2-4 INCH TOTALS OVER A 2-3 HOUR PERIOD WILL BE POSSIBLE.

DISCUSSION...REGIONAL RADAR IMAGERY AT 22Z SHOWED A BROKEN LINE OF
THUNDERSTORMS EXTENDING FROM NH INTO WRN CT/SRN NY/NRN NJ JOINING
WITH A LARGER CLUSTER OF CONVECTION IN ERN PA. THUNDERSTORMS MORE
SCATTERED IN NATURE WERE OBSERVED WEST OF THE BROKEN LINE...FROM
VT INTO ERN NY...JUST AHEAD OF A SLOW MOVING COLD FRONT EXTENDING
SWWD FROM NRN NY INTO CNTRL PA. 21Z DATA FROM THE SPC MESOANALYSIS
PAGE DEPICTED AN AXIS OF RELATIVELY HIGHER MLCAPE EXTENDING FROM
NRN NJ INTO CNTRL AND SRN NEW ENGLAND...WITH VALUES RANGING
BETWEEN 1000-1500+ J/KG CO-LOCATED WITH WEAKLY ANOMALOUS
PRECIPITABLE WATER VALUES BETWEEN 1.4 AND 1.6 INCHES.

WATER VAPOR SHOWED A STRONG UPPER TROUGH AMPLIFYING INTO THE OHIO
VALLEY WITH NEUTRAL HEIGHT FALLS OVER THE NORTHEAST...WHICH SHOULD
CONTINUE AND ALLOW THE COLD FRONT TO REMAIN SLOW MOVING IN THE
SHORT TERM. VAD WIND PLOTS AT 850 MB FROM OKX AND ALY SHOWED
ROUGHLY 20 KT AT 22Z...WITH A SMALL 5-10 KT INCREASE EXPECTED VIA
THE RAP OUT AHEAD OF THE ENEWD MOVING CONVECTION ONGOING ACROSS
ERN PA.

UNIDIRECTIONAL FLOW FROM THE SOUTHWEST IS CURRENTLY IN PLACE WITH
OBSERVED STORM MOTIONS OF 20-30 KT. THE MODEST INCREASE IN LOW
LEVEL FLOW MAY HELP TO ENHANCE CONVECTIVE COVERAGE AND PERIODS OF
TRAINING FROM NRN NJ/SRN NY INTO NEW ENGLAND OVER THE NEXT 3-5
HOURS WITH 2-4 INCH RAINFALL TOTALS POSSIBLE. THESE AMOUNTS MAY
CAUSE FLASH FLOODING IN A FEW MORE SENSITIVE AREAS ACROSS THE
REGION. WHILE REDUCTIONS TO CAPE AFTER SUNSET COULD BE A
SIGNIFICANT LIMITING FACTOR FOR OBTAINING RAINFALL CORES HIGH
ENOUGH TO GENERATE FLASH FLOODING...THE SYNOPTIC FORCING ALOFT MAY
HELP TO COMPENSATE.

OTTO

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

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

LAT...LON   42957311 42927222 42367216 41497263 40397397
            40347521 41857434