Storm Prediction Center Mesoscale Discussion 1258

   Mesoscale Discussion 1258
   NWS Storm Prediction Center Norman OK
   0805 PM CDT Wed Jun 11 2025

   Areas affected...portions of eastern Iowa into extreme southwest
   Wisconsin and far northwestern Illinois

   Concerning...Severe Thunderstorm Watch 408...

   Valid 120105Z - 120230Z

   The severe weather threat for Severe Thunderstorm Watch 408
   continues.

   SUMMARY...Severe winds may continue with an ongoing cluster of
   thunderstorms for at least a couple more hours, east of Severe
   Thunderstorm Watch 408. It is unclear how much longer/far downstream
   the threat will persist.

   DISCUSSION...A cluster of thunderstorms continues to produce mainly
   severe gusts while propagating along a baroclinic boundary. Along
   this boundary, 8+ C/km low-level lapse rates and 30 kts of effective
   bulk shear remain, with the DVN 00Z observed sounding showing a
   deep, dry boundary layer in place (extending up to 700 mb). Such
   conditions favor the continuance of an organized severe gust threat,
   with the primary negating factor likely being nocturnal cooling. It
   is unclear how quickly nocturnal stabilization of the boundary layer
   will begin limiting severe gust potential, but at least a couple of
   severe gusts may occur as far east as far northwestern IL.

   ..Squitieri.. 06/12/2025

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

   ATTN...WFO...LOT...MKX...DVN...ARX...DMX...

   LAT...LON   42109278 42559240 42829200 42939141 42458947 42238911
               41988903 41678931 41548979 41569052 41729155 41879226
               41959245 42109278 

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