This evening’s and tonight’s severe weather threats approaching from both the north and west. Ongoing Tornado Watch #424 in effect for much of Wisconsin



Mesoscale Discussion 1487
   NWS Storm Prediction Center Norman OK
   0356 PM CDT Wed Aug 11 2021

   Areas affected...Portions of eastern IA...far northeastern MO...and
   northwestern IL

   Concerning...Severe potential...Watch possible 

   Valid 112056Z - 112330Z

   Probability of Watch Issuance...40 percent

   SUMMARY...If storms develop and can be sustained, then the threat
   for large hail and damaging winds would increase. Convective trends
   will be closely monitored, with watch issuance possible.

   DISCUSSION...Recent attempts at convective initiation have been
   noted across eastern IA along/east of a surface cold front. This
   region is on the southern extent of an upper trough over central
   Canada and the Upper Midwest, with minimal mid-level height falls
   noted. Still, latest mesoanalysis suggests that airmass just ahead
   of the front is extremely unstable and uncapped, with MLCAPE of
   3500-4500 J/kg present. Latest VWP from KDVN shows winds veering
   with height through mid levels and strengthening to around 45-50 kt
   above 3 km. Related 35-40 kt of deep-layer shear would be supportive
   of supercells. The presence of steep mid-level lapse rates and a
   very favorable thermodynamic environment suggests a threat for large
   hail with any supercell that can form and be sustained. Damaging
   downdraft winds would also be a concern. The main question is
   whether any robust storms will be able to form given the weak
   large-scale ascent aloft. This region will be closely monitored for
   signs of increasing convective coverage/intensity, with watch
   issuance possible.

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