Storm Prediction Center Mesoscale Discussion 242

   Mesoscale Discussion 0242
   NWS Storm Prediction Center Norman OK
   0933 AM CDT Wed Mar 19 2025

   Areas affected...parts of northeastern Iowa...northern
   Illinois...southern Wisconsin

   Concerning...Severe potential...Watch unlikely 

   Valid 191433Z - 191630Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Thunderstorms approaching the Greater Milwaukee and
   Chicago metropolitan areas may continue to pose a risk for small to
   marginally severe hail before weakening by midday into early
   afternoon.

   DISCUSSION...Observational data indicate some recent intensification
   of thunderstorm activity in an arcing northeastward advancing band
   spreading into/across parts of southern Wisconsin and northern
   Illinois.  Based on forecast soundings, this convection is rooted
   within elevated moisture return and destabilization based near the
   700 mb level, beneath an initial surge of cooling further aloft.  

   Most unstable CAPE may be as high as 750+ J/kg along this corridor,
   with shear within the elevated convective layer strong, which may
   continue to support sub-severe to marginally severe hail in stronger
   cells another few hours.  Into midday day, as activity spreads
   towards/into the Greater Milwaukee and Chicago vicinities, the
   latest Rapid Refresh suggests that this convection will probably
   tend to weaken as storm inflow trends less unstable.

   ..Kerr/Leitman.. 03/19/2025

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

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

   LAT...LON   42819067 43178997 42848824 41578784 40938846 41208911
               41958954 42819067