Mesoscale Discussion 1578
   NWS Storm Prediction Center Norman OK
   1140 PM CDT Tue Aug 25 2020

   Areas affected...Parts of northeastern Minnesota...northern
   Wisconsin and the western Upper Peninsula of Michigan

   Concerning...Severe potential...Watch unlikely 

   Valid 260440Z - 260715Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Intensifying thunderstorm development is possible
   overnight, particularly near the western Wisconsin/Upper Michigan
   border area by 2-3 AM CDT.  This may include a couple hour period
   where storms may become capable of producing severe hail.  It is not
   anticipated that a severe weather watch will be needed, but trends
   will be monitored.

   DISCUSSION...Nocturnal southwesterly low-level jet strengthening
   (30-40 kt at 850 mb) has occurred across the mid Missouri Valley
   toward the western Lake Superior vicinity.  A gradual veering of
   this jet to a greater west-southwesterly component is likely across
   the Upper Midwest through 06-08z, while short wave perturbations
   also begin to flatten mid-level ridging near the central
   Canadian/U.S. border area.

   Isentropic ascent near and north/east of the nose of the low-level
   jet is already contributing to the initiation of thunderstorm
   activity (west-southwest of Hibbing MN as of 0430Z).  Activity may
   still be suppressed by inhibition associated with a plume of warm
   elevated mixed-layer air, and this may remain the case another
   couple of hours.  However, models suggest a more substantive
   intensification of thunderstorm activity is possible closer to
   07-08Z, as this forcing spreads east-southeastward toward the
   Wisconsin/Upper Michigan state border vicinity.  This appears to be
   closer to the northeastern edge of the strong capping, and may
   coincide with a rapid increase in low-level moisture associated with
   the 850 mb jet.

   CAPE for moistening parcels rooted above a stable boundary-layer may
   increase in excess of 2000 J/kg, in the presence of sufficient shear
   for mid-level updraft rotation, beneath moderate to strong
   northwesterly mid/upper flow.  Severe hail may be the primary severe
   hazard in initial stronger development, before activity increases in
   coverage/grows upscale.  The boundary layer may remain too cool to
   support an appreciable risk for strong surface gusts associated with
   downbursts.  However, trends will continue to be monitored for the
   possibility of convective organization which could support
   increasing risk for strong surface gusts overnight.

   ..Kerr/Grams.. 08/26/2020

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

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

   LAT...LON   48039281 46598835 45948697 45158765 46049069 46949303
               48039281