Storm Prediction Center Mesoscale Discussion 471

   Mesoscale Discussion 0471
   NWS Storm Prediction Center Norman OK
   0351 PM CDT Fri Apr 18 2025

   Areas affected...parts of cntrl and srn Lower Michigan

   Concerning...Severe potential...Watch possible 

   Valid 182051Z - 182245Z

   Probability of Watch Issuance...40 percent

   SUMMARY...The potential for thunderstorm initiation along and just
   south of a warm frontal zone across lower Michigan is being
   monitored for a possible severe weather watch issuance, as this may
   be accompanied by increasing risk for severe hail and wind by 6-8 PM
   EDT.

   DISCUSSION...A weak perturbation, within larger-scale anticyclonic
   flow on the northwestern periphery of prominent mid-level ridging,
   will continue to progress across and northeast of the middle
   Mississippi Valley through late afternoon.  Associated forcing for
   ascent appears to have aided a flare up of convection approaching
   the Greater Milwaukee vicinity, and latest Rapid Refresh suggests
   that this may contribute to erosion of inhibition associated with
   elevated mixed-layer air across southern Lower Michigan by the
   22-00Z time frame.  

   As this occurs, the moistening boundary-layer along and south of a
   warm frontal zone (downstream of a weak surface low migrating across
   southern Wisconsin/northern Illinois) may become characterized by
   CAPE in excess of 1000 J/kg within the next couple hours, in the
   presence of strong deep-layer shear.  Although calibrated HREF and
   NCEP SREF guidance indicates highest probabilities for thunderstorm
   development evolving above/to the north of the warm frontal zone,
   initiation of storms closer to and just south of the frontal zone
   will provide the highest potential for organizing and intensifying
   into a severe hail and wind threat.

   ..Kerr/Smith.. 04/18/2025

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

   ATTN...WFO...DTX...IWX...GRR...

   LAT...LON   43118598 43578274 42438293 41798653 42558615 43118598 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN