ZCZC SPCSWOMCD ALL ACUS11 KWNS 211751 SPC MCD 211751 NJZ000-NYZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-211945- 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 NNNN