Storm Prediction Center Mesoscale Discussion 801

   Mesoscale Discussion 0801
   NWS Storm Prediction Center Norman OK
   1123 AM CDT Wed May 20 2026

   Areas affected...portions of the Mid-Atlantic

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

   Valid 201623Z - 201800Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Widely scattered thunderstorms will pose a risk for
   damaging wind gusts and isolated large hail this afternoon and
   evening. A Severe Thunderstorm Watch will be needed soon.

   DISCUSSION...Latest surface observations depict a cold front
   extending from central New York southwestward through north-central
   and western Pennsylvania into southeast Ohio. Ahead of this cold
   front, temperatures are warming into the 90s across portions of the
   Mid-Atlantic, with surface dewpoints in the low/mid 60s F. Continued
   heating of this air mass is supporting 1000-1500 J/kg MLCAPE, with
   further destabilization anticipated through the afternoon hours.

   Recent satellite/radar imagery has shown increasing convective
   coverage ahead of the aforementioned cold front as remaining
   inhibition is eroded. With stronger mid/upper-level flow remaining
   displaced to the northwest, only modest effective shear is analyzed
   across the region (generally 20-30+ kts per latest mesoanalysis).
   This will be sufficient to support updraft organization with
   multicells, and perhaps marginal supercells, likely. Steep low-level
   lapse rates, well-mixed boundary layer profiles, and surface
   dewpoint depressions exceeding 20-25 F will promote the potential
   for damaging wind gusts, particularly with any more organized
   clusters that develop. Isolated instances of large hail may also
   accompany any more robust updrafts despite weak mid-level lapse
   rates (as sampled by the 12z PIT/IAD observed soundings). A Severe
   Thunderstorm Watch will be needed soon.

   ..Chalmers/Hart.. 05/20/2026

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

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

   LAT...LON   40687798 40987676 40987614 40907587 40747568 40397553
               39967560 39437589 39147621 38927665 38687793 38597862
               38587907 38767959 39117993 39388003 39737992 40107959
               40247926 40687798 

   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN