Storm Prediction Center Mesoscale Discussion 2070

   Mesoscale Discussion 2070
   NWS Storm Prediction Center Norman OK
   0222 PM CDT Fri Aug 21 2026

   Areas affected...southwest Wisconsin...far eastern Iowa...and
   northern Illinois

   Concerning...Severe potential...Watch likely 

   Valid 211922Z - 212115Z

   Probability of Watch Issuance...80 percent

   SUMMARY...The threat for damaging wind gusts, large hail, and
   perhaps a brief tornado or two is expected to increase through the
   remainder of this afternoon. A severe thunderstorm watch will likely
   be required in the next 1-2 hours.

   DISCUSSION...Recent trends in visible satellite and radar data
   indicate incipient thunderstorm development occurring along a cold
   front pushing into southwest WI. Additional deepening cumulus is
   also noted within the pre-frontal warm sector from east-central into
   southeast IA. Another storm has recently intensified along the
   outflow boundary from earlier storms east of Rockford, IL. The 18Z
   DVN sounding is likely a good representation of the ambient
   environment with a moist profile through the lowest 3km AGL largely
   contributing to MLCAPE of around 2500 J/kg. Moreover, the sounding
   featured veering winds with height with 35-40 kt of deep-layer shear
   oriented largely perpendicular to the surface front.  

   Prevailing west to west-northwest low-level winds ahead of the front
   may allow for air mass recovery to occur over portions of
   south-central WI into north-central IL later this afternoon,
   effectively creating a wider warm sector for the ongoing WI storms
   to spread southeast. The environment described above appears
   supportive of organized storm modes, including supercells with an
   attendant risk for mainly large hail initially. While low-level
   shear is not expected to be overly strong, some potential exists for
   a brief tornado or two, especially with any supercells that can
   favorably interact with the outflow boundary.

   Latest CAM guidance suggests that an initially more discrete storm
   mode will gradually transition to a broken band by late afternoon or
   this evening, at which point the threat for damaging wind gusts
   would increase.

   ..Mead/Smith.. 08/21/2026

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

   ATTN...WFO...LOT...ILX...MKX...DVN...ARX...

   LAT...LON   41259092 42809081 43479025 43188956 42078849 41318806
               40808810 40308864 40178918 40188983 40359032 40729091
               41259092 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN