Storm Prediction Center Mesoscale Discussion 1690

   Mesoscale Discussion 1690
   NWS Storm Prediction Center Norman OK
   1223 PM CDT Tue Jul 21 2026

   Areas affected...portions of the Mid-Atlantic into the Northeast

   Concerning...Severe potential...Watch likely 

   Valid 211723Z - 211930Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Increasing storm coverage is expected through the
   afternoon and will necessitate a watch.

   DISCUSSION...Recent composite radar indicates increasing shower and
   thunderstorm coverage across eastern Pennsylvania on the leading
   edge of mid 70s dewpoints as they advect northward. Most of this
   activity is moving away from the greater moisture/instability, but
   continued northward destabilization is anticipated. In addition,
   broken cloud cover across southeast Pennsylvania and New Jersey will
   result in greater instability within this zone. The leading edge of
   a 50 knot mid-level jet (centered around 5-6km) has been sampled by
   the CCX VWP within the last half an hour. As this overspreads the
   warm sector, shear will be in place for storm organization,
   including supercells. Damaging winds will be the primary threat, but
   some large hail and a few tornadoes will also be possible. 

   The greatest threat will be across southeast Pennsylvania and New
   Jersey, where the greater instability is in place. However, as the
   warm front lifts northeastward, the threat could extend into
   southeast New York and Connecticut this afternoon.

   ..Bentley/Mosier.. 07/21/2026

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

   ATTN...WFO...BOX...OKX...ALY...PHI...BGM...CTP...LWX...

   LAT...LON   39187437 38877495 39457648 39867689 41097690 42277653
               42657593 42727456 42487358 42037309 41257279 40597287
               40417378 39187437 

   MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN