Mesoscale Discussion 1264
   NWS Storm Prediction Center Norman OK
   0312 PM CDT Sat Jul 18 2020

   Areas affected...MN...NORTHWEST WI

   Concerning...Severe potential...Watch likely 

   Valid 182012Z - 182145Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorm development is expected by late
   afternoon or early evening. Very large hail, damaging winds, and
   perhaps a couple of tornadoes will be possible. Watch issuance is
   likely by 21Z.

   DISCUSSION...20Z surface analysis depicts a surface low over
   southwest MN, with a cold front trailing southwestward into the
   central Plains, a diffuse stationary front extending northeastward
   into the northern MN, and a retreating outflow boundary extending
   eastward toward the Twin Cities, then southeastward across western
   WI. Strong to extreme instability has developed from the vicinity of
   the surface low eastward along and south of the outflow boundary,
   with MLCAPE increasing into the 4000-5000 J/kg range per recent
   mesoanalyses. The magnitude of instability combined with effective
   shear of 35-45 kt is resulting in a very favorable severe
   thunderstorm environment from far eastern SD into southern/central
   MN. 

   Uncertainty remains regarding the timing and location of
   thunderstorm development, with increased midlevel cloud cover moving
   in from the southwest. Confidence is still high that deep convection
   will eventually initiate by early this evening somewhere across
   western/central MN, as a shortwave trough over the northern Plains
   approaches the region. Initial discrete convection would pose a
   threat of very large hail, given very favorable instability and
   deep-layer shear. A tornado or two also could not be ruled out with
   any cell that can favorably interact with the outflow boundary. With
   time, consolidating outflows will favor upscale growth, with
   corridors of damaging wind possible this evening as convection
   spreads eastward and eventually southeastward into tonight.

   ..Dean/Hart.. 07/18/2020

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

   ATTN...WFO...DLH...ARX...MPX...FGF...FSD...

   LAT...LON   45009595 45899540 46089514 46889397 47219302 47219151
               46979091 46689090 45909093 45099113 44449204 44099389
               43919527 44099635 45009595