Severe thunderstorms are rapidly developing in Iowa. A severe thunderstorm watch may soon be issued for areas of southern Wisconsin and northern Illinois, that could include portions of the the Chicago Metro area

Mesoscale Discussion 1465
   NWS Storm Prediction Center Norman OK
   0310 PM CDT Tue Aug 10 2021

   Areas affected...Portions of southern and eastern Wisconsin

   Concerning...Severe potential...Watch likely 

   Valid 102010Z - 102215Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Watch likely by 21Z.

   DISCUSSION...A boundary has become more diffuse as if lifts north
   across southern Wisconsin over the past hour with occasional
   convective attempts. If storms go up along this boundary, a watch
   may be needed soon as extreme instability (MLCAPE around 4500 J/kg)
   should support explosive storm development. Averaged effective shear
   between KGRB and KDVN 19Z RAOBs shows around 25 knots. This would be
   sufficient for multicell storm modes with a threat for both large
   hail and damaging winds. 

   However, even if storms do not develop along this boundary, a watch
   is likely eventually as storms move in from the west. Storms across
   eastern Iowa have started to organize and it appears they may be
   clustering in northeast Iowa. This may be the beginning of upscale
   growth into an MCS which would likely track across southern
   Wisconsin. A watch is likely by 21Z.

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