SPC AC 200530

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 AM CDT Wed Oct 20 2021

   Valid 201200Z - 211200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
   IOWA AND SOUTHERN MINNESOTA...

   ...SUMMARY...
   Thunderstorms with isolated large hail are possible today across
   northern Iowa and southern Minnesota, primarily during the morning
   and early afternoon.

   ...Portions of the Midwest/Mid MS Valley into the Great Lakes...
   A mid/upper-level low is forecast to move from near the Sandhills
   region of Nebraska this morning eastward toward southern Lake
   Michigan by early Thursday. A surface low is forecast to gradually
   deepen as it moves from eastern NE into parts of lower MI, as an
   attendant cold front moves through portions of the Midwest, mid MS
   Valley, and Great Lakes. 

   Elevated convection will likely be ongoing at the start of the
   period across northeast NE/southeast SD/northwest IA, within an
   environment characterized by relatively steep midlevel lapse rates
   and cool temperatures aloft, MUCAPE of 500-1000 J/kg, and effective
   shear of 30-40 kt. This environment will support an isolated large
   hail threat, as convection spreads eastward through the day in
   conjunction with the mid/upper-level low. 

   Further south toward the mid MS Valley, substantial MLCINH will
   likely inhibit surface-based storms along and ahead of the cold
   front, though moistening near the 850 mb level may support some
   slightly elevated convection. While small hail or locally gusty
   winds cannot be ruled out with convection along the front, the
   threat for severe hail/wind appears too limited for probabilities in
   this area. 

   Elevated convection will likely spread into lower MI late tonight
   into early Thursday morning. MUCAPE of up to 500 J/kg may support a
   few stronger storms, though any severe threat appears rather limited
   at this time.  

   ...North-central Gulf Coast...
   Relatively rich low-level moisture will stream northward into
   portions of LA and southern MS/southwest AL during the day today,
   along the western periphery of a surface ridge over the Southeast
   CONUS. As this occurs, moderate buoyancy will support scattered
   thunderstorms near the coast this morning, with convection expected
   to spread further inland with time by afternoon. While weakly
   veering wind profiles may favor some organization with the strongest
   storms, poor midlevel lapse rates and generally modest low/midlevel
   flow may tend to limit the severe risk in this area, though small
   hail and gusty winds cannot be ruled out.

   ..Dean/Wendt.. 10/20/2021

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