MESOSCALE PRECIPITATION DISCUSSION 0536
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
307 PM EDT WED SEP 30 2015
 
AREAS AFFECTED...EASTERN MAINE 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 301905Z - 010105Z
 
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 MAINE. 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. STRONG INFLOW OFF THE ATLANTIC IS HELPING
SUPPLY ABUNDANT MOISTURE RESULTING IN EFFICIENT RAINFALL. 

RADAR ESTIMATES AND OBSERVATIONS SHOW RAINFALL RATES GENERALLY
BETWEEN 0.25" AND 0.5" AN HOUR...BUT LOCAL RATES AS HIGH AS AROUND
1.5" AN HOUR REMAIN LIKELY IN EMBEDDED CONVECTIVE ELEMENTS. THIS
IS ESPECIALLY TRUE ALONG COASTAL MAINE. SOME BREAKS IN THE CLOUDS
JUST AHEAD OF THE COLD FRONT HAVE ALLOWED FOR A NARROW LINE OF
CONVECTION TO DEVELOP ACROSS EASTERN MASSACHUSETTS TO JUST OFF THE
SOUTHEAST MAINE COAST. BASED ON THE LOCATION OF THE FRONT AND
RECENT SATELLITE TRENDS...THINK MOST OF THIS ENHANCED CONVECTION
WITH RATES AROUND 1" AN HOUR WILL STAY OFF THE MAINE COAST. BUT
LOCATIONS RIGHT ALONG THE COAST COULD GET CLIPPED BY A BRIEF
PERIOD OF HIGHER RATES WITH THIS BAND...WHICH IF DOES OCCUR WOULD
CONTINUE THE FLOOD THREAT OVER THE ALREADY SATURATED GROUND.

THE HRRR AND EXPERIMENTAL ESRL HRRR BOTH CONTINUE TO HAVE A DECENT
HANDLE ON CURRENT CONDITIONS. EXPECT THE HEAVIEST PRECIPITATION TO
BE EAST OF MAINE BY 8-10 PM LOCAL TIME. THIS STILL LEAVES SEVERAL
MORE HOURS OF STEADY TO BRIEFLY HEAVY RAINFALL IN AN AREA THAT HAS
ALREADY RECEIVED AMOUNTS AVERAGING BETWEEN 2-6". EXPECT ADDITIONAL
RAINFALL BETWEEN 1.5-3"...HIGHEST ALONG THE CENTRAL AND NORTHERN
COAST OF MAINE. 

CHENARD

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

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

LAT...LON   46976784 46626685 46036627 45186599 44536646 
            43956812 43437060 43986978 44496917 45376931 
            46306900 46786849