SPC AC 171954

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0254 PM CDT Fri Jul 17 2020

   Valid 172000Z - 181200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   NORTH DAKOTA THROUGH NORTHERN MINNESOTA INTO NORTHWEST WISCONSIN...

   ...SUMMARY...
   A significant severe weather event is expected this afternoon
   through tonight over parts of North Dakota, northern Minnesota, and
   northwest Wisconsin. Widespread damaging wind is the primary threat,
   though large hail and a few tornadoes are also possible.

   ...Northern Plains through Upper Mississippi Valley...

   Previous outlook appears on track, and only change has been to
   expand the moderate risk a bit farther north to reflect current
   trends. Initial thunderstorm development is underway over northern
   ND. This activity should evolve into an organized MCS with bowing
   segments and embedded mesovortices capable of widespread damaging
   wind as it advances through an environment characterized by strong
   northward destabilization and 35-45 kt effective bulk shear.

   ..Dial.. 07/17/2020

   .PREV DISCUSSION... /ISSUED 1121 AM CDT Fri Jul 17 2020/

   ...ND to WI/Upper MI...
   Morning water vapor loop shows fast westerly flow across the
   northern tier of states, with an embedded low-amplitude shortwave
   trough over eastern MT.  Southerly low-level winds are present
   across the Dakotas, with local VADs showing 20-30 knots at 1-2km. 
   These winds are helping to transport 70s surface dewpoints
   northward, yielding an axis of MLCAPE exceeding 4000 J/kg later
   today from central ND into western MN.  Thunderstorms are expected
   to form early this afternoon as forcing overspreads the returning
   moisture, with a few supercells capable of large hail, damaging
   winds, or perhaps a tornado over western/central ND.  All guidance
   lends confidence that these storms will congeal into one or more
   bowing structures by this evening over eastern ND.  Storms will
   track rapidly eastward at 40-50 knots across parts of MN and into
   northern WI and upper MI overnight.  

   Given the very favorable thermodynamic profiles in place, the strong
   westerly flow aloft, and the consistent model guidance, it appears
   possible that a derecho will occur this evening and tonight from ND
   to WI - with the threat of a corridor of widespread and significant
   damaging winds.  Have expanded the MDT/ENH risks eastward into parts
   of WI/Upper MI where the bowing complex appears most likely to track
   late tonight.  Have also expanded the ENH southward into more of
   central MN due to uncertainty of how far south the MCS might
   develop.

   ...VA/NC...
   Warm/humid surface conditions are present today over parts of VA/NC,
   with moderate CAPE values and a weak front moving into the area. 
   Scattered afternoon thunderstorms are expected to develop
   along/ahead of the front from central VA into northern NC, with
   activity sagging southward through the afternoon and early evening. 
   Winds aloft are weak, limiting convective organization.  However,
   disorganized multicell and pulse convection may pose a risk of
   gusty/damaging winds in the strongest downdrafts.

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