MESOSCALE PRECIPITATION DISCUSSION 0677
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 AM EDT MON SEP 19 2016
 
AREAS AFFECTED...PORTIONS OF THE NRN MID-ATLANTIC STATES 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 190643Z - 191230Z
 
SUMMARY...INCREASING COVERAGE OF HEAVY RAINFALL WITH TRAINING AXES
COULD ALLOW FOR A FEW LOCATIONS IN THE NRN MID-ATLANTIC REGION TO
SEE 4-6 INCHES OF RAINFALL THROUGH 12Z. DESPITE DRY ANTECEDENT
CONDITIONS...FLASH FLOODING WILL BE POSSIBLE.

DISCUSSION...LONG LOOP OF THE CIRA LAYERED PRECIPITABLE WATER (PW)
PRODUCT SHOWED THE COMBINING OF TROPICAL MOISTURE FROM
POST-TROPICAL CYCLONE JULIA AND DEEP MOISTURE ADVECTING INTO THE
MID-ATLANTIC AND NORTHEAST AHEAD OF AN UPPER TROUGH AXIS
APPROACHING FROM THE WEST. REGIONAL RADAR IMAGERY FROM 0615Z
SHOWED BANDS OF SHOWERS OVER ERN PA TO NRN VA...ALIGNING WITHIN
AREAS OF LOW LEVEL CONFLUENCE AHEAD OF A LOW LEVEL TROUGH AXIS.
ALOFT...UPPER LEVEL FLOW SUPPORTED AN AXIS OF UPPER DIFFLUENCE
ALONG THE MID-ATLANTIC REGION AHEAD OF AN APPROACHING 70-100 KT
JET AXIS. 

WHILE BETTER INSTABILITY WAS IN PLACE TOWARD THE COAST ALONG WITH
SLIGHTLY STRONGER LOW LEVEL FLOW...BETTER SUPPORTING AXES OF
TRAINING HEAVY RAINFALL...FORCING FOR ASCENT WAS DISPLACED
SLIGHTLY WWD AS OF 06Z. HOWEVER...WITH THE ADVANCING TROUGH AXIS
FROM THE WEST...THE COMBINATION OF LOW LEVEL CONFLUENCE AND UPEPR
LEVEL DIVERGENCE/DIFFLUENCE WILL BEGIN TO OVERLAP FROM SW TO
NE...EXTENDING FROM MUCH OF S-CNTRL VA INTO ERN PA AND NJ. WHILE
FLASH FLOOD GUIDANCE IS AS HIGH AS 4+ INCHES IN 3 HOURS DUE TO A
LACK OF RAINFALL OVER THE PAST 2 WEEKS...IF TRAINING AXES OF 1-2+
IN/HR RAINS SIT OVER AN AREA LONG ENOUGH...FLASH FLOODING MAY
OCCUR WITH THE POTENTIAL FOR 3-6 HOUR RAINFALL TOTALS OF 3-5
INCHES.

OTTO

ATTN...WFO...AKQ...ALY...BGM...CTP...LWX...OKX...PHI...RAH...
RNK...

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

LAT...LON   41607308 41417257 40937254 40127385 39087471 
            38407545 37757619 36697758 36427843 36977904 
            38187858 39677724 41047549 41527398