Storm Prediction Center Mesoscale Discussion 1620

   Mesoscale Discussion 1620
   NWS Storm Prediction Center Norman OK
   0343 PM CDT Wed Jul 09 2025

   Areas affected...Portions of
   Maryland...Delaware...Pennsylvania...and New Jersey

   Concerning...Severe Thunderstorm Watch 497...

   Valid 092043Z - 092245Z

   The severe weather threat for Severe Thunderstorm Watch 497
   continues.

   SUMMARY...Convective trends are being monitored for the need for
   downstream watch issuance across parts of Maryland, Delaware,
   Pennsylvania, and New Jersey as storms spread east through early
   evening.

   DISCUSSION...Regional radar mosaics continue to show a slow, but
   steady, increase in convective coverage across southern PA and parts
   of northern MD as lift associated with a mid-level impulse continues
   to migrate east and overspreads a moderately buoyant air mass.
   Regional VWPs continue to sample 30-40 knot mid-level flow
   associated with the upper feature, but the nebulous forcing for
   ascent and modest mid-level lapse rates appear to be modulating
   convective intensity and longevity of more discrete cells across
   PA/MD. While the convective parameter space is supportive of
   organized/severe convection, it remains unclear how intense
   convection will become over the next few hours. 

   Further south into eastern MD and DE, confidence is higher in a
   severe wind threat later this evening. A squall line is slowly
   organizing across central VA and is expected to continue
   intensifying over the next few hours (see recently issued MCD #1619
   for additional details). Recent surface observations and MLCAPE
   analyses show a plume of rich low-level moisture/buoyancy extending
   into southern DE/southeast MD, which should maintain the convective
   line as it spreads east into the evening hours. Slow storm motions
   cast some uncertainty on exactly when a downstream watch will be
   needed, but recent high-res guidance suggest a damaging wind threat
   will begin to materialize between 23-01 UTC.

   ..Moore.. 07/09/2025

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

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

   LAT...LON   39057445 38737476 38387493 38137505 37887521 37787541
               37867579 38117608 38547620 39057635 39297654 39487691
               39717717 39927727 40127722 40397661 40527587 40457514
               40247461 40057432 39787409 39477417 39057445 

   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN