MESOSCALE DISCUSSION 2255
   NWS STORM PREDICTION CENTER NORMAN OK
   0553 PM CDT THU OCT 13 2011
   
   AREAS AFFECTED...ERN VA AND WRN AND NRN MD
   
   CONCERNING...TORNADO WATCH 866...
   
   VALID 132253Z - 140030Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 866 CONTINUES.
   
   THE THREAT FOR ISOLATED TORNADOES AND ISOLATED DAMAGING WIND SHOULD
   PERSIST THROUGH EARLY EVENING MAINLY ACROSS NERN VA THROUGH WRN AND
   NRN MD. HOWEVER...OVERALL THREAT SHOULD BEGIN A GRADUAL DECREASE BY
   01Z.
   
   EARLY THIS EVENING A WARM FRONT EXTENDS FROM CNTRL MD THROUGH NRN VA
   AND WNWWD INTO THE OH VALLEY. MOIST WARM SECTOR PERSIST SOUTH OF THE
   FRONT WITH UPPER 60S-70F DEWPOINTS. HOWEVER...INSTABILITY REMAINS
   MARGINAL OWING TO MODEST LAPSE RATES PROFILES. STORMS WILL CONTINUE
   DEVELOPING WITHIN WEAKLY CAPPED WARM SECTOR AND IN ASSOCIATION WITH
   VORT MAX EJECTING NWD THROUGH VA THIS EVENING. VWP DATA INDICATE
   35-40 KT 0-6 KM SHEAR OVER THE MID ATLANTIC...AND LOW LEVEL
   HODOGRAPHS ARE MAXIMIZED NEAR THE WARM FRONT WHERE THE FLOW IS
   BACKED TO SELY WITH 0-1 KM STORM RELATIVE HELICITY FROM 100-200
   M2/S2. SOME FURTHER INCREASE IN LOW LEVEL SHEAR MAY OCCUR DURING THE
   NEXT COUPLE HOURS AS THE LLJ STRENGTHENS. ISOLATED TORNADOES REMAIN
   POSSIBLE ANYWHERE WITHIN THE WATCH AREA...BUT THE GREATEST TORNADO
   THREAT APPEARS TO BE ACROSS NERN VA INTO NRN AND WRN MD AS STORMS
   LIFT NWD AND INTERACT WITH THE BOUNDARY. OVERALL THREAT SHOULD BEGIN
   A GRADUAL DECREASE BY 01Z AS THE BOUNDARY LAYER COOLS AND
   STABILIZES.
   
   ..DIAL.. 10/13/2011
   
   
   ATTN...WFO...PHI...AKQ...LWX...
   
   LAT...LON   38937800 39407702 39157618 38317593 37447608 37297672
               37547742 37897772 38937800