Mesoscale Discussion 0424
   NWS Storm Prediction Center Norman OK
   1123 AM CDT Tue Apr 21 2020

   Areas affected...northeast
   Virginia...Maryland...Deleware...southeast Pennsylvania and New
   Jersey

   Concerning...Severe potential...Watch possible 

   Valid 211623Z - 211830Z

   Probability of Watch Issuance...40 percent

   SUMMARY...The threat for isolated damaging wind may undergo some
   increase by early to mid afternoon over the Middle Atlantic region.
   Trends will continue to be monitored for a possible WW.

   DISCUSSION...A band of low-topped convection currently extends from
   eastern PA southwest into West Virginia moving east at around 45 kt.
   Activity is developing along a cold front and in association with
   deeper ascent attending a progressive shortwave trough. The
   downstream warm sector is only weakly unstable due to widespread
   pre-frontal rain and clouds. A relatively narrow corridor of partial
   clearing is occurring just ahead of the cold front, though tendency
   has been for dewpoints to mix down into the 30s F, due to a
   relatively shallow moist layer evident on the 12Z Dulles ROAB. The
   Wallops RAOB indicated a somewhat deeper near-surface moist layer
   with surface dewpoints in the upper 40s. As temperatures rise into
   the low-mid 60s F and where low-mid 40s near-surface dewpoints can
   be maintained, sufficient instability (300-500 J/kg MLCAPE) might
   develop to support updrafts capable of isolated damaging wind gusts.
   This will be promoted by inverted-V boundary layers and potential
   for southwesterly winds of 40-45 kt in the 1-2 km layer to be
   transported to the surface within some of the convective cores.

   ..Dial/Hart.. 04/21/2020

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

   ATTN...WFO...OKX...PHI...AKQ...CTP...LWX...

   LAT...LON   39987621 40707561 40917479 40647402 39877417 39277468
               38227616 38057738 38967741 39987621