MESOSCALE PRECIPITATION DISCUSSION 0243
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
718 PM EDT THU SEP 12 2013
 
AREAS AFFECTED...EASTERN ME...SOUTHERN NEW ENGLAND 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 122317Z - 130217Z
 
SUMMARY...EASTERN ME AND SOUTHERN NEW ENGLAND ARE EXPECTED TO HAVE
TRAINING CONVECTION FOR AN ADDITIONAL 2-3 HOURS.  REGIONAL FLASH
FLOODING IS POSSIBLE IN THESE AREAS.

DISCUSSION...CONVECTION CONTINUES TO DEVELOP AND ORGANIZE AHEAD OF
A SURFACE COLD FRONT WITHIN THE RIGHT ENTRANCE REGION OF AN UPPER
LEVEL JET.  PRECIPITABLE WATER VALUES OF 1.75-2 INCHES EXIST
ACROSS THE REGION, IN THE 90TH TO 95TH PERCENTILES FOR
MID-SEPTEMBER.  THIS HAS HELPED CONTINUE HOURLY RAINFALL RATES OF
1-2 INCHES WITHIN STRONGER THUNDERSTORM ACTIVITY.  SUFFICIENT 0-3
KM WIND SHEAR HAS BEEN ORGANIZING BANDS OF CONVECTION ACROSS THE
REGION.  CURRENTLY, TWO BANDS EXIST, WITH ONE ACROSS CENTRAL ME
WITH A NEW ONE ORGANIZING ACROSS SOUTHERN NEW ENGLAND. 
INDICATIONS ARE THAT 30+ KNOTS OF LOW-LEVEL WIND SHEAR ACCOMPANIED
BY 30 KNOTS OF 850 HPA INFLOW EXIST ACROSS THE AREA PER REGIONAL
VAD WIND PROFILES.  

THE 21Z RAP GUIDANCE INDICATES CAPES REMAIN IN THE 1000-2000 J/KG
RANGE AND THAT 00Z IS WHEN THE CAPE VALUES WANE REGIONALLY BELOW
1000 J/KG.  WINDS IN THE 850-400 HPA LAYER INDICATE THAT CELL
MOTION COULD CONTINUE TO BE ROUGHLY ALONG THE AXES OF THE TWO
CONVECTIVE BANDS, WHICH HAVE BEEN SLOWLY EDGING EASTWARD WITH
TIME.  SAB INDICATES THAT THE ACTIVITY, PARTICULARLY ACROSS
SOUTHERN NEW ENGLAND, COULD PERSIST FOR ANOTHER FEW HOURS.  THE
21Z RAP INDICATES THAT THE LOW-LEVEL INFLOW AND 0-3 KM SHEAR
SHOULD BEGIN TO ABATE AROUND 02Z.  TO ACCOMMODATE THE ABOVE IDEAS,
CHOSE A VALID TIME CLOSE TO 02Z.  OUR THOUGHTS ARE THAT ACTIVITY
ACROSS ME COULD CARRY A FLASH FLOOD THREAT UNTIL AROUND 00Z, WITH
ACTIVITY FARTHER SOUTH CARRYING A THREAT THROUGH 02Z.  

ROTH

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

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

LAT...LON   45846733 46686771 46376864 45636942 44167080 43287159
            42847242 42297396 41147428 40447406 40617270 40857210
            41276997 41746969 41996976 42527032 42987056 43586998
            43916869 44066825 44426745 44756689 45006677 45626727
            45846733