SPC AC 020542

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1242 AM CDT Tue Jun 02 2020

   Valid 021200Z - 031200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN
   MINNESOTA TO SOUTHERN WISCONSIN...

   ...SUMMARY...
   Severe thunderstorms are expected later today from the middle
   Missouri and upper Mississippi Valleys into the Great Lakes.
   Damaging wind gusts, large hail and a couple of tornadoes are
   possible, with the greatest threat expected from southern
   Minnesota/northern Iowa into central Wisconsin.

   ...Middle MO Valley to Upper Great Lakes...

   Early-morning water-vapor imagery depicts a strong short-wave trough
   along the AB/SK border, extending into western MT. Southern extent
   of this feature is forecast to move across the Dakotas later today
   which will flatten the northern Plains ridge, then advance into the
   upper Great Lakes tonight. In response, synoptic front is forecast
   to move across northwestern WI - into southern MN - southeastern SD
   by 18z, then drape itself from central WI - MN/IA border - central
   NE by early evening. Latest model guidance strongly suggests
   surface-based parcels will remain capped through 22z but convection
   could begin to develop along the cool side of the front a few hours
   earlier where short-wave forcing is more notable. Latest CAMs
   suggest isolated elevated thunderstorms could initiate over eastern
   SD by early afternoon, then spread/develop east along/near the
   frontal zone into southern MN. A corridor of strong instability is
   expected across this region into central WI and there is increasing
   confidence that early-afternoon convection will eventually take
   advantage of this downstream buoyancy and ingest moist/unstable
   boundary-layer inflow. If so, robust convective updrafts are likely
   with adequate shear for organized multi-cell clusters and perhaps a
   few supercells. Forecast soundings suggest very large hail could
   occur, but most likely with supercell structures. Otherwise, if an
   MCS evolves ahead of the front, there is some concern for damaging
   winds given the instability. This activity should propagate across
   southern WI into lower MI after sunset, possibly spreading into
   northern OH during the pre-dawn hours.

   ...Eastern WY...

   Surface front is forecast to settle south across the High Plains of
   eastern WY with northeasterly upslope flow expected to develop by
   late afternoon. Boundary-layer heating and orographic forcing
   suggest isolated supercells may develop along the southern fringe of
   modest westerly mid-level flow. This activity should spread
   southeast toward the NE Panhandle during the evening.

   ..Darrow/Lyons.. 06/02/2020

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