Mesoscale discussion – update on Severe Thunderstorm Watch

Mesoscale Discussion 1550
   NWS Storm Prediction Center Norman OK
   0458 PM CDT Sat Jul 20 2019

   Areas affected...Northern Illinois

   Concerning...Severe Thunderstorm Watch 532...

   Valid 202158Z - 202300Z

   The severe weather threat for Severe Thunderstorm Watch 532

   SUMMARY...The greatest severe weather threat remains along the
   Illinois lake shore in WW 532.

   DISCUSSION...The severe threat has likely waned in the near term in
   western portions of severe thunderstorm watch 532. The primary
   severe threat is now along the Lake Michigan shoreline in Illinois
   where there are ongoing storms and additional development is
   expected. Storms continue to develop over the convectively enhanced
   cold pool in the southern Great Lakes. Given the extreme instability
   (4000+ MUCAPE and steep lapse rate environment (7.5 to 8 C/km),
   these storms will continue to pose a threat for both large hail and
   damaging winds despite only marginal shear (~25 kts). Expect new
   development to continue on the southern and western flank as the
   outflow boundaries continue to sag south. This will lead to storms
   likely impacting downtown Chicago within the hour. Eventually, the
   outflow boundary will likely move far enough south into a more
   capped environment which should limit additional development south
   of Cook county.
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