MESOSCALE PRECIPITATION DISCUSSION 0394
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1111 AM EDT WED JUN 29 2016
 
AREAS AFFECTED...PORTIONS OF NH & ME 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 291511Z - 292111Z
 
SUMMARY...THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE AND
INTENSITY OVER THE NEXT SEVERAL HOURS.  HOURLY RAIN RATES UP TO
2", WITH LOCAL AMOUNTS OF 2-4", COULD LEAD TO FLASH FLOODING OVER
SATURATING SOILS.

DISCUSSION...A STACKED/DEEP-LAYERED CYCLONE NEAR MONTREAL IS
EDGING EASTWARD.  UNDER THE BASE OF THE CYCLONE, A SHORTWAVE SOUTH
OF THE LOW IS SEEN ON WATER VAPOR IMAGERY MOVING THROUGH NY STATE.
 CUMULUS STREETS ARE FORMING BETWEEN EASTERN VT, AND THE STRATUS
FIELD ACROSS ME IS STARTING TO BREAK UP/THIN, GIVING WAY TO THE
DEVELOPMENT OF CUMULI.  AS IMPLIED BY THE CLOUD STREETS, VAD WIND
PROFILES SHOW 15-25 KT INFLOW AT 850 HPA, WITH VALUES CLOSER TO 30
KTS AT 700 HPA.  THE FLOW IS UNIDIRECTIONAL OUT OF THE
SOUTH-SOUTHWEST WITH HEIGHT.  MLCAPES ARE PASSING 500 J/KG ACROSS
PORTIONS OF NEW ENGLAND PER THE 14Z SPC MESOANALYSES. 
PRECIPITABLE WATER VALUES OF 1.3-1.6" LIE ACROSS THE AREA PER
RECENT GPS DATA, 12Z SOUNDINGS, AND RECENT RAP FORECASTS.

THE EXPECTATION IS FOR CONVECTION TO CONTINUE STRENGTHENING AND
INCREASING IN COVERAGE AS INSTABILITY CONTINUES TO BUILD TODAY,
LIKELY INTO THE 1000-1500 J/KG RANGE MLCAPE-WISE.  THE
UNIDIRECTIONAL FLOW WITH HEIGHT IMPLIES CELL TRAINING REMAINS THE
MOST LIKELY FLASH FLOOD THREAT.  WITH TIME, THE 850 HPA SLICE OF
THE COLD FRONT IS EXPECTED TO EDGE EAST ACROSS PORTIONS OF NH AND
THROUGH CENTRAL ME, WHICH COULD CAUSE THE CONVECTION TO SHIFT
EASTWARD WITH TIME.  THE ORIENTATION OF THE THICKNESS PATTERN
ITSELF ALSO IMPLIES SOME SLIGHT FORWARD PROPAGATION WITH TIME. 
HOURLY RAIN RATES UP TO 2", WITH LOCAL AMOUNTS IN THE 2-4" RANGE,
ARE POSSIBLE DURING THE MPD PERIOD.  SOILS ACROSS NORTHERN NEW
ENGLAND WERE PARTIALLY SATURATED BY YESTERDAY'S RAINFALL, WHICH
TOTALED 6-8" LOCALLY.  THE 06Z SSEO NEIGHBORHOOD PROBABILITIES
REFLECT THIS, SHOWING A 50%+ CHANCE OF EXCEEDING THE THREE HOUR
FLASH FLOOD GUIDANCE BEGINNING IN THE 16-19Z PERIOD IN NORTHERN
ME. FLASH FLOODING IS A CONCERN.

ROTH

ATTN...WFO...BTV...CAR...GYX...

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

LAT...LON   47526848 47326796 46996773 45766777 44326921 
            43307060 42757138 43097192 43747223 45007210 
            46147101 47147006 47466929