SPC AC 182004

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0304 PM CDT Sat Jul 18 2020

   Valid 182000Z - 191200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
   MINNESOTA INTO WESTERN WISCONSIN...

   ...SUMMARY...
   Damaging thunderstorm gusts, large hail and isolated tornadoes are
   possible this afternoon and tonight across portions of the Upper
   Midwest and Upper Great Lakes.

   ...Upper Midwest and Upper Great Lakes regions...

   Only modest adjustments have been made to previous outlook which
   appears on track.

   A cold front extends from northwest MN to a surface low in west
   central MN, then into southeast SD and northeast NE. What is left of
   a weakening outflow boundary has advanced northward and extends
   across south central MN. The atmosphere continues to destabilize in
   this region with MLCAPE from 3000-4500 J/kg, primarily along and
   south of the outflow boundary. Thunderstorms should develop this
   afternoon along cold front and especially in proximity to the cold
   front/outflow boundary intersection over central MN. Activity will
   subsequently spread east into the Great Lakes region during the
   evening. Effective bulk shear from 40-45 kt will support some
   supercells, before activity evolves into lines and clusters as it
   develops eastward. Large hail and a couple of tornadoes will be
   possible initially, with threat transitioning to primarily damaging
   wind this evening.

   ..Dial.. 07/18/2020

   .PREV DISCUSSION... /ISSUED 1122 AM CDT Sat Jul 18 2020/

   ...Upper Midwest...
   Latest surface analysis shows a cold front extending from northern
   MN southward into western SD.  A weak low along the front will be
   over southwest MN later this afternoon, enhancing convergence and
   leading to scattered thunderstorm development.  Visible satellite
   imagery shows clear skies in this region, with southerly low-level
   winds helping to return 70s dewpoints to the area.  Forecast
   soundings across southern/central MN into western WI show a very
   unstable air mass later today with MLCAPE values of 5000+ J/kg.

   Rapid thunderstorm development is expected in the 20-23z period,
   with sufficient deep-layer vertical shear to support a few
   supercells capable of very large hail.  Low-level flow/shear is not
   particularly strong, but the degree of instability and proximity to
   surface boundaries could result in a tornado or two as well. 
   Activity is likely to congeal into an MCS as it tracks eastward into
   western WI this evening.

   An ENG risk area has been added to the region with highest
   confidence of storm coverage/severity.  However, various model
   solutions suggest some potential that the area of concern could grow
   southeastward this evening into more of southeast MN and central WI.
   This will be re-evaluated in later outlook updates.

   ...Carolinas...
   Similar to yesterday scattered and relatively disorganized
   thunderstorms are expected to form over parts of NC, with slow
   development southeastward into SC.  The strongest cells may
   occasionally produce gusty winds.

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