MESOSCALE PRECIPITATION DISCUSSION 0279
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1146 AM EDT SAT JUN 27 2015
 
AREAS AFFECTED...DISTRICT OF COLUMBIA...MARYLAND...NORTHERN
VIRGINIA...EASTERN WEST VIRGINIA...SOUTHERN PENNSYLVANIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 271600Z - 272200Z
 
SUMMARY...BROAD SYNOPTIC LIFT WITH INCREASING INSTABILITY WITHIN
CONFLUENT LOW LEVEL FLOW TO FOCUS HEAVY RAINFALL POTENTIAL. THIS
IS LIKELY TO LEAD TO SCATTERED FLASH FLOODING.  

DISCUSSION...CYCLOGENESIS IS ALLOWING FOR A STRONG LOW TO DEVELOP
OVER NORTHERN OH.  GIVEN THE STRENGTH AND BREADTH OF THE SYNOPTIC
FORCING/HEIGHT FALLS A STATIONARY FRONT OFFSHORE THE MOUTH OF THE
CHESAPEAKE BAY IS ALREADY RESPONDING WITH SOME NORTHWARD MOVEMENT
WITH INCREASING SOUTHEASTERLY FLOW. THIS ALONG WITH REINFORCING
SOUTHWESTERLY FLOW OUT OF THE MOUNTAINS WILL RAPIDLY ADVANCE THE
WARM FRONT BUT MORE IMPORTANTLY ALLOW FOR CONFLUENCE OF ATLANTIC
AND TENNESSEE VALLEY LOW LEVEL FLOW REGIMES ACROSS NORTHERN
VA...INCREASING TOTAL PWATS OVER 2". THIS COULD BE PARTICULARLY
ENHANCED FROM THE ATLANTIC/BAY AS ORIENTATION OF FLOW SHOULD ALLOW
FOR ENHANCED CHANNELING OF MOISTURE/INSTABILITIES THROUGH THE
EASTERN VA RIVER VALLEYS.  THIS SHOULD BE EFFECTIVE AT DEVELOPING
DEEPER MORE EFFICIENT RAINFALL CORES EVEN THOUGH INSTABILITIES ARE
MARGINAL INITIALLY.

THESE INITIAL CELLS HAVE THE HIGH LIKELIHOOD FOR SLOW FORWARD
MOTIONS WAITING IN RESPONSE UPSTREAM PRE-FRONTAL CONVECTIVE
LINE(S) CURRENTLY ACROSS EASTERN KY/SOUTHERN WV.  INCREASING
INSTABILITIES THROUGHOUT THIS TIME...MAXIMIZING NEAR 1500-2000
J/KG ABOUT 20-21Z AHEAD OF THE SECOND LINE WILL MAKE A STRONGER
ROUND OF STORMS WITH INCREASED RATES TO 2"+/HR COMPOUNDING THE
SITUATION TOWARD LIKELY FLASH FLOODING CONDITIONS.

HI-RES CONVECTION ALLOWING MODELS ARE CONSISTENT  IN PAINTING A
SWATH OF 2-4" TOTALS OVER A NARROW SSW-NNE AXIS BY 22Z...JUST
SLIGHT DIFFERENCES IN LOCATION...BUT GENERALLY CENTERED ACROSS N
VA INTO THE DISTRICT AND CENTRAL MD...THE NMMB AND ARW ARE MOST
AGGRESSIVE/FASTEST SUGGESTING ISOLATED POCKETS OF EVEN HIGHER
POTENTIAL WHICH COULD POTENTIALLY LEAD TO A DECENTLY SIZED AREA OF
FLASH FLOODING CONDITIONS ACROSS CENTRAL MD/DC/N VA...PARTICULARLY
GIVEN THE VERY LOW FLASH FLOOD GUIDANCE...SATURATED SOILS...AND
URBAN SETTING. 

PLEASE SEE RECENT SPENES FOR DISCUSSION REGARDING MODERATE
RAINFALL WITH A FOCUS TOWARD PROLONGED FLOODING CONDITIONS WITH
SOME WEAK EMBEDDED CONVECTIVE ELEMENTS ACROSS WESTERN MD/SW PA/NE
OH.

GALLINA

ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...RLX...RNK...

ATTN...RFC...MARFC...OHRFC...SERFC...

LAT...LON   40407685 40317607 39897588 39467604 38357629 
            37397622 37267677 37217700 37437877 37527985 
            37578038 37858069 38997951 39767835