Marginal risk of severe thunderstorms across the Chicago area tonight

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0239 PM CDT Sat Sep 14 2019

   Valid 142000Z - 151200Z

  ...Upper Midwest to the central Great Plains...
   Elevated thunderstorms are ongoing in western IA on the leading edge
   of a low-level warm theta-e advection plume. This plume and
   attendant zone of ascent will spread east-northeast across the Upper
   MS Valley into tonight in advance of a low-amplitude shortwave
   trough near the ND/MB border that will move east-southeast into Lake
   Superior. This elevated convection will pose a threat for isolated
   large hail, mainly this evening into tonight with a probable decay
   cycle this afternoon. A risk for locally damaging winds may also
   develop tonight towards the IA/IL/WI border region if a cluster can
   become semi-organized. 

   In the wake of the warm advection regime, storm initiation will
   depend on weak low-level ascent along a surface trough that extends
   southwestward across NE/KS. Stronger surface heating and deeper
   mixing is expected along the trough in KS, with lesser mixing depths
   and a greater probability of maintaining MLCIN through the afternoon
   in the warm sector farther northeast. Thus, surface-based
   thunderstorm development should be sparse and may struggle to be
   sustained during the late afternoon/early evening. If surface-based
   storms can form as far northeast as southern MN this afternoon,
   vertical shear profiles will be sufficient for supercells. Weaker
   vertical shear is expected with southwestward extent into southwest
   KS, where high-based storms would pose a threat for isolated severe
   wind and hail. 

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