MESOSCALE PRECIPITATION DISCUSSION 0531
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 PM EDT TUE SEP 29 2015
 
AREAS AFFECTED...E WEST VIRGINIA...VIRGINIA...W MARYLAND...EXT SW
PENNSYLVANIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 291912Z - 300012Z
 
SUMMARY...BAROCLINIC SHIELD PRECIPITATION SETS THE STAGE WITH
MODERATE TOTALS BEFORE INCREASED CONVECTION EVOLVES BY 00Z WITH
INCREASED FLASH FLOOD THREAT.

DISCUSSION...WITH THE MAIN UPPER LOW DISPLACED WELL WEST OVER SE
MO...WEAK SHORTWAVE RIDGING AND INCREASED DIVERGENCE ALOFT IS IN
PLACE TO ENHANCE THE ADVANCING S/W OVER SW VA ATTM...ALLOWING FOR
INCREASED DEEPENING OF THE MID-LEVEL CIRCULATION INCREASING
INFLOW/LOW LEVEL CONVERGENCE.  AT THE SAME TIME INCREASING THE
BAROCLINIC SHIELD AND ISENTROPIC ASCENT FROM THE SE INTO THE
HIGHER TERRAIN OF NW VA/E WV.  25-30 KTS OF LOW LEVEL FLOW FROM
THE PIEDMONT INTO THE EASTERN ATLANTIC/GULF STREAM OFF NC
CONTINUES TO PUMP VERY MOIST AIR IN THE LOW LEVELS AND SWLY FLOW
PULLS DEEP MOISTURE ALOFT FOR A NEARLY SATURATED PROFILE WITH TPWS
IN THE 2.0-2.25" RANGE...ALLOWING FOR EFFICIENT OVERRUNNING WITH
.5"/HR RATES SEEN ACROSS A VAST AREA LIKELY TO INCREASE IN
COVERAGE ACROSS WV INTO W MD/SW PA.  

RECENT VIS LOOP SHOWS AN UPTICK IN CONVECTIVE DEVELOPMENT ALONG
AND AHEAD OF A WNW-ESE MID-LEVEL TROF. PARTICULARLY OVER
VA...THESE CELLS ARE TAPPING A BIT OF INCREASED INSTABILITY FROM
SOME SOLAR INSOLATION THAT OCCURRED IN THE CLEARING ACROSS SE VA
AND NC.  THE CAPES ARE LIMITED TO ABOUT 500-1000 J/KG ALLOWING FOR
SOME INCREASED RATES OF UP TO 1.0"-1.25"/HR.  RATES ARE NOT LIKELY
TO LEAD TO FLASH FLOODING BUT WITH MODERATE TOTALS IN ADVANCE
COULD LEAD TO PROLONGED FLOODING PROBLEMS. 

HI-RES CAMS PARTICULARLY THE ESRL EXPERIMENTAL HRRR...THE
HRRR...THE NSSL-WRF...THE ARW...NMMB AND 16Z RAP STRONGLY SUGGEST
A SIMILAR EVOLUTION WITH THE WAVE LIFTING NORTH TOWARD SW PA BY
00Z BUT WITH WEAKER SWLY FLOW TOWARD THE COAST...THE ADVANCEMENT
OF THE BOUNDARY IS STALLED ALLOWING FOR INCREASED
CONVERGENT/CONFLUENT FLOW TO POOL ALONG A LINE FROM FREDRICK
COUNTY VA THROUGH CENTRAL VA TOWARD LUNENBERG.  THIS INCREASED
CONFLUENCE ALLOWING FOR INCREASED AND MORE VIGOROUS CONVECTION TO
DEVELOP WITH MUCH HIGHER RATES AS THEY ADVANCE SLOWLY EAST
PARTICULARLY OVER N VA...INCREASING FLASH FLOOD THREAT.   

GALLINA

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

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

LAT...LON   39887958 39857891 39707830 39187762 38777741 
            37747728 37107732 36697778 36697851 37087930 
            37597972 37918003 38268029 38588074 39058076 
            39648032