MESOSCALE PRECIPITATION DISCUSSION 0036
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
132 PM EST WED FEB 24 2016
 
AREAS AFFECTED...VIRGINIA...CENT MARYLAND...DISTRICT OF
COLUMBIA...SE PENNSYLVANIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 241831Z - 250031Z
 
SUMMARY...HYDROLOGICAL FLOODING CONCERN INITIALLY WITH ELEVATED
STRONG CELLS CAPABLE OF HOURLY RATES IN EXCESS OF LOW FFG VALUES. 
CONFLUENCE OF MOISTURE STREAMS TOWARD 00Z TO POSE INCREASED FF
COVERAGE TOWARD 00Z.  

DISCUSSION...SYNOPTIC SETUP FOR SEVERE WX ACROSS THE
MID-ATLANTIC...PLEASE SEE SWOMCD AND SEVERE/TORNADO WATCH
INFORMATION FROM SPC FOR ADDITIONAL DETAILS.

ALONG WITH THE SEVERE THREAT...GROUND CONDITIONS ACROSS THE
MID-ATLANTIC ARE CONDUCIVE FOR FLASH FLOODING GIVEN DORMANT/HARD
GROUND AND THUNDERSTORMS CAPABLE OF RATES NEAR OR IN EXCESS OF
SHORT TERM FFG VALUES (TYPICALLY LESS THAN 1.0"/HR) ACROSS THE
DISCUSSION AREA.  A SHORTWAVE SEEN IN WV ACROSS THE LOWER
APPALACHIANS OF NC/TN AND ASSOCIATED SPEED MAX ARE COINCIDENT WITH
DRY SLOT PROVIDING ASCENT IN DPVA ZONE TOWARD THE NORTHEAST.  WV
ALSO INDICATES A COOLING OR SLIGHT MOISTENING OF THE DRY SLOT WITH
A NARROW RIBBON OF COOLER/MORE MOIST AIR ALIGNED WITH THE
INCREASING CONVECTION ACROSS SW VA/W CENT NC AND CENT SC
ATTM...PROVIDING SOME ADDITIONAL INCREASE IN RAINFALL EFFICIENCY
OF THESE CELLS.  HOWEVER...TPWS ARE TEETERING AROUND 1.0" CELL
EFFICIENCY ALONG WITH FORWARD MOTION SHOULD LIMIT FLASH FLOODING
CONDITIONS TO BE QUITE ISOLATED WITHIN THE STRONGEST OF CORES 
NEAR BUT LESS LIKELY TO EXCEED THE LOWERED FFG VALUES IN THE NEAR
TERM (NEXT 1-3 HOURS)...PARTICULARLY AS CELLS WILL BE MORE
ELEVATED IN NATURE AS THE LOW LEVEL WEDGE OF COOLER AIR IS SLOWLY
ERODED. 

FURTHER EAST...THE DEEP MOISTURE AXIS IS ORIENTED N-S OVER E NC
INTO E VA AND S MD ATTM...WITH 1.5 TPW VALUES NEAR THE NC COAST
INCREASING TO OVER 1.25" JUST NORTH OF THE WARM FRONT NEAR THE DC
METRO AREA.  WITH HEIGHT FALLS FURTHER WEST AND SHORTWAVE LIFTING
NORTH...THE SOUTHERLY LLJ OF 50-60 KTS WILL INCREASE TO 70 KTS AT
850MB BUT NOT ADVANCE EASTWARD MUCH...ALLOWING FOR FURTHER
WESTWARD SURGE OF THE WARM FRONT ALREADY MOVING INTO CENTRAL MD
OFF THE BAY.  INSTABILITY WILL CONTINUE TO LIFT NORTH ON THE
SOUTHERLY FLOW WITH MUCAPES IN THE 1000 J/KG RANGE INTO THE
PENINSULAR NECKS OF E VA POSSIBLY INTO S MD PRODUCING SOME
EMBEDDED CONVECTION AND MODERATE SHOWERS FOR SOME ISOLATED FF
THREATS IN THE LOWER GUIDANCE. 

OF LARGER CONCERN IS THE TIMING OF THE WESTERN LINE LIFTING
NORTHEAST AND CONFLUENCE WITH THE NORTHWARD EXPANDING WARM SECTOR
WILL ALLOW FOR CONVECTION TO BECOME A BIT MORE SURFACE ROOTED AS
WELL AS INCREASED MOISTURE FLUX FOR RAINFALL EFFICIENCIES TOWARD
23-00Z THIS EVENING...POTENTIALLY REACHING AS FAR N AS SE PA. ONCE
THE MOISTURE AND LIFT ARE IN BETTER PROXIMITY ACROSS N VA/CENTRAL
MD...RAINFALL EFFICIENCY TOWARD 1.25-1.5"/HR ARE LIKELY WITH RAIN
TOTALS IN THE 1-2" PARTICULARLY WITH INCREASED COVERAGE FOR SHORT
TERM/ACCIDENTAL TRAINING OF THESE EXPANDING HEAVY RAIN CORES.  

GALLINA

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

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

LAT...LON   40987640 40247555 39627579 39087582 37357612 
            36857676 36747740 36957817 36817929 37157960 
            38287875 39247774 40347723