Mesoscale Discussion 1048
   NWS Storm Prediction Center Norman OK
   1251 PM CDT Mon Jun 21 2021

   Areas affected...northern VA...much of MD...northern
   DE...central-eastern PA...western NJ

   Concerning...Severe potential...Severe Thunderstorm Watch likely 

   Valid 211751Z - 211945Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Clusters of strong to severe thunderstorms capable
   primarily of isolated to widely scattered damaging gusts, are
   possible this afternoon into the early evening.  A severe
   thunderstorm watch will likely be needed over most of the discussion
   area by mid afternoon.

   DISCUSSION...Visible-satellite imagery shows a cluster of strong to
   locally severe thunderstorms over WV moving eastward.  This
   thunderstorm cluster will approach the eastern panhandle of WV and
   far western MD (to the east of severe thunderstorm watch #299)
   during the next few hours.  A cumulus field has developed over the
   remainder of the discussion area from VA north to the NY/PA border. 
   It seems possible convective initiation occurs over central PA near
   State College over the next hour.

   Surface analysis indicates the airmass has destabilized early this
   afternoon with temperatures generally in the upper 80s deg F with
   upper 60s to lower 70s dewpoints.  Modifying the the Pittsburgh, PA
   8am raob for current conditions over central PA yields around 2000
   J/kg MLCAPE.  The Dulles, VA 8am raob was noticeably less unstable
   this morning compared to the Pittsburgh, PA raob.  However, strong
   heating and moistening of the boundary layer east of the higher
   terrain has resulted in moderate buoyancy over this area too.  

   The strong heating across this broad region has steepened low-level
   lapse rates.  As storms move into the region from the west, the
   lapse rate profiles will support the potential for strong downdrafts
   with the heavier water-loaded cores or small bow-shaped segments
   that may evolve.  Peak gusts ranging from 50-70 mph are possible
   with the strongest storms.  

   It is uncertain whether isolated storms will develop over eastern PA
   during the afternoon or whether the thunderstorm risk will be
   delayed until storms arrive from the west.  This uncertainty is due
   in part to large-scale subsidence likely suppressing activity on the
   northwest periphery of Tropical Storm Claudette.

   ..Smith/Hart.. 06/21/2021

   ...Please see www.spc.noaa.gov for graphic product...

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

   LAT...LON   41967569 41977758 39627938 38167972 37727908 37857820
               39317564 40657447 41497491 41967569