MESOSCALE PRECIPITATION DISCUSSION 0535
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1030 AM EDT WED SEP 30 2015
 
AREAS AFFECTED...NORTHEAST MASSACHUSETTS...NEW
HAMPSHIRE...CENTRAL/SOUTHERN MAINE 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 301430Z - 302030Z
 
SUMMARY...MODERATE TO HEAVY RAINS AND EMBEDDED CONVECTION WILL
CONTINUE TO SPREAD NORTHEAST RESULTING IN A CONTINUED FLOOD RISK
INTO THIS AFTERNOON.

DISCUSSION...RADAR IMAGERY CONTINUES TO SHOWS A LARGE AREA OF
MODERATE TO HEAVY RAINS SPREADING ACROSS NEW ENGLAND. RECENT
SATELLITE TRENDS SHOWS THE PRECIPITATION IN A STEADY STATE OR EVEN
INTENSIFYING GIVEN SLIGHTLY COOLING CLOUD TOPS.

THE ENVIRONMENT REMAINS VERY FAVORABLE FOR ASCENT...WITH STRONG
LOW LEVEL FRONTOGENESIS INTERACTING WITH AN APPROACHING SHORTWAVE
AND STRONGLY DIVERGENT PATTERN ALOFT IN THE RIGHT ENTRANCE REGION
OF AN UPPER JET STREAK. CAPE IS LACKING...BUT CONVECTIVE UPDRAFTS
SEEN IN SATELLITE AND A FEW LIGHTNING STRIKES SUGGEST THE STRONG
INFLOW OFF THE OCEAN IS HELPING PROVIDE AT LEAST SOME WEAK
INSTABILITY HELPING ENHANCE RAINFALL RATES. 12Z SOUNDINGS SHOW
PRECIPITABLE WATER VALUES AROUND 2" ACROSS EASTERN NEW
ENGLAND...WHICH IS NEAR RECORD VALUES FOR THIS TIME OF YEAR. WET
BULB ZERO HEIGHTS ARE ALSO NEAR RECORD HIGH VALUES. BOTH OF THESE
SUGGEST HIGHLY EFFICIENT RAINFALL WILL CONTINUE.

RADAR ESTIMATES AND OBSERVATIONS SHOW RAINFALL RATES GENERALLY
BELOW 0.5" AN HOUR...BUT LOCAL RATES AS HIGH AS AROUND 1-1.5" AN
HOUR REMAIN LIKELY IN EMBEDDED CONVECTIVE ELEMENTS. THIS IS
ESPECIALLY TRUE FROM EASTERN MASSACHUSETTS INTO SOUTEHRN NEW
HAMPSHIRE AND THE SOUTHERN HALF OF MAINE. 

THE HRRR AND EXPERIMENTAL ESRL HRRR BOTH SEEM TO HAVE A DECENT
HANDLE ON CURRENT CONDITIONS AND SEEM TO REPRESENT A PLAUSIBLE
FORECAST EVOLUTION. THROUGH 20Z THESE SUGGEST AN ADDITIONAL 2-4"
IS LIKELY ACROSS THE REGION...ESPECIALLY FROM SOUTHEAST NEW
HAMPSHIRE INTO SOUTHERN MAINE...WITH ISOLATED HIGHER AMOUNTS.
WHILE RATES SHOULD GENERALLY STAY BELOW FLASH FLOOD GUIDANCE...THE
HIGH STORM TOTAL AMOUNTS WILL LIKELY CONTINUE TO SATURATE THE
GROUND...INCREASING THE FLOOD AND/OR FLASH FLOOD RISK INTO THIS
AFTERNOON.  

CHENARD

ATTN...WFO...BOX...CAR...GYX...

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

LAT...LON   45986734 44476702 42696940 42087065 42107173 
            43317214 44627129 45347029 45966870