MESOSCALE DISCUSSION 0740
   NWS STORM PREDICTION CENTER NORMAN OK
   1110 PM CDT WED MAY 06 2009
   
   AREAS AFFECTED...VA/EASTERN MD/DE AND CENTRAL/NORTHERN NC
   
   CONCERNING...TORNADO WATCH 257...
   
   VALID 070410Z - 070545Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 257 CONTINUES.
   
   TORNADO WATCH 257 CONTINUES UNTIL 08Z...WITH THE PRIMARY SEVERE
   THREAT ACROSS VA. MONITORING FOR AN INCREASING SEVERE THREAT NORTH
   OF WW 257 ACROSS NORTHERN VA AND THE ADJACENT DELMARVA VICINITY.
   
   EARLIER PERSISTENT SUPERCELLS ACROSS SOUTHERN VA HAVE REMAIN FAIRLY
   ISOLATED/SOMEWHAT INHIBITED BY NEAR SURFACE CINH AND A LACK OF
   APPRECIABLE FORCING ACROSS THE WARM SECTOR. NONETHELESS...STRONG LOW
   LEVEL WIND FIELDS AND 300+ 0-1KM SRH PER WSR-88D VWP DATA FROM
   RALEIGH/BLACKSBURG/WAKEFIELD REMAIN CONDITIONALLY FAVORABLE FOR LOW
   LEVEL MESOCYCLONES. AS AN UPSTREAM SHORTWAVE TROUGH APPROACHES FROM
   THE TENNESSEE VALLEY...THE MOST LIKELY CORRIDOR FOR SEVERE POTENTIAL
   MAY DEVELOP/INCREASE ACROSS THE NORTH/NORTHWEST PORTION OF WW 257
   INTO THE ADJACENT DELMARVA ALONG A CORRIDOR OF LOW LEVEL
   CONVERGENCE/EXISTING NORTHEAST-SOUTHWEST ORIENTED BAND OF
   CONVECTION. WITHIN THIS CORRIDOR...EVEN WITH LIMITED SURFACE BASED
   BUOYANCY...STRONG WIND FIELDS WOULD SUPPORT THE DEVELOPMENT OF SMALL
   BOWS/PERHAPS EMBEDDED SMALL SUPERCELLS CAPABLE OF DAMAGING WINDS AND
   PERHAPS A TORNADO OR HAIL. THE NEED FOR A WATCH NORTH OF EXISTING
   TORNADO WATCH 257 IS UNCLEAR...BUT CONVECTIVE TRENDS WILL BE CLOSELY
   MONITORED OVERNIGHT AS WW 257 OTHERWISE CONTINUES UNTIL 08Z.
   
   ..GUYER.. 05/07/2009
   
   
   ATTN...WFO...PHI...AKQ...LWX...RAH...RNK...
   
   LAT...LON   37207555 35797806 35457967 36657986 39787585 37207555