Storm threat looms for the evening hours over the mid-atlantic:

NWS Tornado PorbabilityNWS Severe Weather Probability

NWS Meso Discussion

 MESOSCALE DISCUSSION 1004
   NWS STORM PREDICTION CENTER NORMAN OK
   1203 PM CDT FRI JUN 01 2012
  
   AREAS AFFECTED…NC…VA…WV…MD…DC…PA
  
   CONCERNING…SEVERE POTENTIAL…TORNADO WATCH LIKELY
  
   VALID 011703Z – 011830Z
  
   PROBABILITY OF WATCH ISSUANCE…80 PERCENT
  
   SUMMARY…THUNDERSTORMS WILL INCREASE THROUGH THE AFTERNOON IN A
   VERY MOIST AND INCREASINGLY UNSTABLE AIRMASS FROM NC NWD ACROSS
   VA…SRN PA…WV PNHDL…AND MD/DC AREA. RECENT TRENDS SUGGEST THAT
   ISOLATED STORMS WILL FIRST POSE A THREAT FOR ISOLATED SEVERE WEATHER
   IN THE FORM OF HAIL/WIND OVER PARTS OF NERN NC AND SERN VA WHERE
   INSTABILITY IS GREATEST BUT SHEAR AND FORCING WILL REMAIN LIMITED
   FOR A TIME. ADDITIONAL SEVERE STORMS ARE LIKELY AS A FORCED SQUALL
   LINE DEVELOPS EAST OF THE APPALACHIANS LATER THIS AFTERNOON. DEEP
   SHEAR AND TORNADO POTENTIAL MAY INCREASE ACROSS THE ENTIRE REGION
   FROM LATE AFTERNOON INTO EVENING AND ONE OR MORE TORNADO WATCHES
   WILL LIKELY BE ISSUED OVER THE NEXT 1-2 HOURS.
  
   DISCUSSION…STRONG FORCED ASCENT WITH A LARGE SCALE TROUGH WAS
   LIKELY RESULTING IN AN INCREASE IN LOW-TOPPED CONVECTION ALONG A
   COLD FRONT NOW SITUATED FROM ERN OH SWD ACROSS WV…EXTREME SWRN VA
   AND ERN TN. EXPECT THAT THIS CONVECTION WILL CROSS THE SPINE OF THE
   APPALACHIANS OVER THE NEXT 2 HOURS. AS THIS FORCING BEGINS TO
   INTERACT WITH GREATER INSTABILITY EAST OF THE MOUNTAINS…MORE
   VIGOROUS STORM DEVELOPMENT IN THE FORM OF BOWING/LEWPING SEGMENTS
   CAN BE EXPECTED. A WEAK FRONTAL WAVE MAY ALSO TAKE FORM WITH TIME
   COINCIDENT WITH AN INCREASE IN STORMS ALONG A WARM FRONT EXTENDING
   ACROSS SRN PA AND INTO THE DELMARVA REGION. IN ADDITION TO WIND
   DAMAGE THREAT WITH STORMS ALONG THE ADVANCING FRONT…AN ENHANCED
   BUT FOCUSED TORNADO THREAT MAY EVOLVE NEAR THE FRONTAL WAVE AND WARM
   FRONT. ONE TORNADO WATCH WILL LIKELY BE NEEDED FROM SRN PA ACROSS
   WRN VA WITHIN THE NEXT HOUR OR SO.
  
   ANOTHER WATCH WILL LIKELY BE NEEDED FROM THE ONGOING STORMS OVER NRN
   NC NWD ACROSS THE VA TIDEWATER AREA. STORMS IN THIS AREA ARE
   DEVELOPING WITH HEATING OF THE DAY AND PERHAPS THE LARGER SCALE
   ASCENT DEVELOPING EAST WITH THE TROUGH. WHILE INSTABILITY IS GREATER
   IN THIS CORRIDOR…DEEP SHEAR AND FORCING ARE LIKELY MORE MARGINAL
   TO SUPPORT A MORE WIDESPREAD IMMEDIATE THREAT OF SEVERE TSTMS
   WIND/TORNADOES. NONETHELESS…SHEAR WILL LIKELY INCREASE
   SUFFICIENTLY WITH TIME ACROSS THIS AREA TO WARRANT A TORNADO WATCH
   AND THIS WATCH WILL LIKELY BE COORDINATED SHORTLY.