Mesoscale Discussion 1713
   NWS Storm Prediction Center Norman OK
   0531 PM CDT Fri Sep 25 2020

   Areas affected...Western Upper Michigan/Wisconsin border vicinity

   Concerning...Severe potential...Watch possible 

   Valid 252231Z - 260030Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Increasing thunderstorm development, including the
   evolution of one or two supercells, appears possible near or just
   west of the Ironwood MI area by 6-7 PM CDT.  This may include
   potential for a tornado or two, in addition to large hail, if
   stronger storm development is maintained along or just south of the
   surface frontal zone.  Some uncertainty lingers, but trends are
   being monitored for the possibility of a severe weather watch.

   DISCUSSION...Latest model output remains suggestive that large-scale
   forcing for ascent, associated with lower/mid tropospheric warm
   advection, may contribute to increasing thunderstorm development in
   the vicinity of a stalled frontal zone near the southern Lake
   Superior shore during the next few hours.  It appears that this may
   be aided by a focused area of strengthening divergence aloft, ahead
   of an approaching low amplitude short wave trough, perhaps
   associated with a coupling of 50-60 kt westerly 500 mb speed maxima.

   Coinciding with the northeastward migration of a surface low across
   the Hayward WI area. toward the Ironwood MI vicinity, a
   southwesterly 850 mb jet is forecast to strengthen from 30-40 kt.
   contributing to sizable clockwise-curved low-level hodographs within
   the warm sector of the low.  Beneath the nose of an
   east-northeastward advecting plume of warm, elevated mixed-layer
   air, and relatively cool mid/upper-levels, modest boundary-layer dew
   points in the lower 60s appear to be contributing to mixed-layer
   CAPE on the order of 1000-1500 J/kg.

   Near the vicinity of the surface frontal zone, the environment may
   become conducive to the evolution of one or two supercells, capable
   of producing large hail and posing potential to produce a tornado,
   before activity possibly consolidates into an organizing cluster
   later this evening.

   ..Kerr/Hart.. 09/25/2020

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

   ATTN...WFO...MQT...GRB...DLH...

   LAT...LON   46539171 47388828 46228887 45889056 45849159 46539171