SPC AC 201621

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1121 AM CDT Mon Jul 20 2020

   Valid 201630Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN
   AND CENTRAL PLAINS...AND OVER THE MIDDLE MISSISSIPPI AND LOWER OHIO
   VALLEYS...

   ...SUMMARY...
   Scattered strong to severe storms capable of large hail and damaging
   winds are expected over parts of the northern and central Plains,
   and the Mid Mississippi and Lower Ohio Valleys.

   ...Northern and Central Plains...
   Morning water vapor shows relatively fast westerly flow aloft
   extending from the northern Rockies and Plains into the Great Lakes
   region.  A more prominent shortwave trough is embedded in the faster
   flow over MT, and is forecast to move into the Dakotas later today. 
   Ample low level moisture is present across the high Plains with
   dewpoints in the 50s and 60s - yielding afternoon MLCAPE values of
   1500-2500 J/kg from western ND to NE.  Remnant convection this
   morning over western SD will drift southeastward and potentially
   intensify with daytime heating, while new activity forms ahead of
   the upper trough and affects the western Dakotas this evening. 
   Forecast soundings appear favorable for large hail and damaging
   winds across this broad area.  Multiple lines and clusters of storms
   should track southeastward through the evening and overnight,
   affecting much of NE and northern KS.  The extent of severe threat
   overnight is less certain, but will maintain the existing SLGT risk
   in case mesoscale organization results in a corridor of overnight
   damaging winds.

   ...Mid MS and Lower OH Valleys...
   Latest surface analysis shows a weak surface boundary extending from
   southwest MO into southern IL and western KY.  A very moist and
   unstable air mass is present to the south of the boundary, with
   dewpoints in the low/mid 70s and strong heating yielding MLCAPE
   values of 2500+ J/kg.  This region is on the southern fringe of
   stronger westerlies, with 500mb winds only in the 20-30 knot range. 
   However, an MCV and associated outflow boundary over western MO will
   move eastward and through parts of this region later today around
   peak heating.  Storms may intensify along this boundary.  Other more
   scattered storms are expected farther east, with multiple CAM
   solutions suggesting the potential for multicell clusters capable of
   gusty/damaging winds.  Given the focused risk of storms and the
   marginal-but-sufficient parameters, have opted to include a SLGT
   risk for the region.

   ..Hart/Moore.. 07/20/2020

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