MESOSCALE PRECIPITATION DISCUSSION 0488
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 PM EDT THU SEP 10 2015
 
AREAS AFFECTED...ERN MD...DE...ERN PA...NJ...SRN NY...SRN
CT...RI...SE MA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 102035Z - 110035Z
 
SUMMARY...HEAVY RAIN RATES WILL PERSIST THROUGH AT LEAST 00Z...AND
MAY YIELD FLASH FLOODING IN VULNERABLE AREAS. BEYOND 00Z...HEAVY
RAIN MAY BE LESS ORGANIZED...BUT COULD RETURN NEAR THE COAST.

DISCUSSION...MULTIPLE SMALL SCALE CONVECTIVE SYSTEMS WERE
STRADDLED TO EITHER SIDE OF A QUASI-STATIONARY FRONT...WHICH WILL
BECOME A WARM FRONT NEAR THE COAST. MOISTURE WAS UNUSUALLY
RICH...LEADING TO NUMEROUS OBSERVATIONS OF ONE INCH RAINFALL
OCCURRING IN 40-60 MINUTES. A LEADING MCS APPROACHING SOUTHEAST
MASSACHUSETTS HAD LIFTED NORTH OF THE INSTABILITY AXIS AND
WEAKENED AS OF 20Z. AN MCS JUST AHEAD OF THE SYNOPTIC LOW WILL BE
OF MORE CONCERN AS IT LIFTS SLOWLY OUT OF EASTERN PA TOWARD
NJ/NY/CT. CONVECTION WAS SHALLOW BUT EFFICIENT GIVEN WARM RAIN
PROCESSES. RADAR LOOPS SHOWED SMALL SCALE CELLS ANCHORED AGAINST
SOME OF THE TERRAIN RISES IN PA/NJ...AND BALANCED AGAINST
SOUTHERLY LOW LEVEL INFLOW TO YIELD LITTLE NET MOVEMENT. THIS TYPE
OF ACTIVITY WILL PRODUCE LOCAL VERY HEAVY RAINFALL EXCEEDING 2
INCHES IN AN HOUR...WHILE THE PARENT RAIN SHIELD DRIFTS
NORTHEASTWARD AT ONLY 10-15 KNOTS PER THE CORFIDI VECTORS FOR
FORWARD PROPAGATION.

ADDITIONAL HEAVY RAINFALL WILL SWEEP THROUGH DELAWARE AND EASTERN
MD. THE LAND MASS HERE AND PERHAPS SOME BAY BREEZE / SEA BREEZE
INTERACTION WILL HAVE CONTRIBUTED TO GREATER INSTABILITY AND
CONVERGENCE. CELLS WHICH IN THEIR FORMATIVE STAGE PRODUCED MORE
THAN 2 INCHES OF RAIN AT ANNAPOLIS WERE MOVING FORWARD AT
2030Z...BUT WILL STILL BE SOME OF THE DEEPEST CORES AS THEY TRACK
THROUGH MD/DE...TAKING FULL ADVANTAGE OF THE 2.10 INCH PW PER SPC
MESOANALYSIS.

SYNOPTIC FORCING DOES NOT COME BACK INTO SYNC UNTIL AFTER DARK
WHEN HEIGHT FALLS AND A FRONTAL WAVE BECOME MORE PRONOUNCED. CAPE
FORECASTS BEYOND 00Z SUGGEST THE MAIN HEAVY RAIN THREAT WOULD BE
NEAR THE IMMEDIATE COAST OF SOUTHERN NEW ENGLAND.

BURKE

ATTN...WFO...AKQ...ALY...BGM...BOX...CTP...LWX...OKX...PHI...

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

LAT...LON   42447149 42346985 41336956 38557335 38037456 
            38327580 39207636 40397578 41397467 41917355