SPC AC 160555

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1255 AM CDT Sun Sep 16 2018

   Valid 171200Z - 181200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE UPPER MIDWEST/UPPER MISSISSIPPI VALLEY AREA...

   ...SUMMARY...
   A few severe storms may occur across parts of the upper
   Midwest/upper Mississippi Valley area Monday.

   ...Synopsis...
   A rather stagnant upper flow pattern is progged over much of the
   U.S. this period, as a trough remains just off the West Coast and
   ridging persists over the southwestern and south-central states. 
   Meanwhile in the east, Florence is progged to move across the upper
   Ohio Valley and central Appalachians as a tropical depression, per
   the latest NHC track forecasts.  

   Aside from Florence, the most prominent surface feature will be a
   cold front, progged to cross eastern Canada and the Great Lakes
   region.  Trailing portions of this front will likely become
   increasingly oriented west-to-east, lingering in a quasi-stationary
   manner across the central Plains and upper Midwest through the
   period.

   ...Southeast South Dakota/southern Minnesota/northern Iowa area...
   As the trailing portion of a cold front lingers across the upper
   Midwest, showers and scattered thunderstorms are expected across
   portions of the area.  While a weakly capped boundary layer should
   largely hinder surface-based storms, elevated convection --
   especially after dark in conjunction with low-level jet development
   -- is expected just north of the boundary.  With fairly steep lapse
   rates aloft expected, and with the southern fringe of stronger
   mid-level southwesterlies near and just north of the surface front,
   a few stronger/locally severe storms may evolve.  Should a
   surface-based storm or two develop in the warm sector by late
   afternoon, locally damaging winds would be possible.  Otherwise,
   hail appears to be the primary risk across this area with a few of
   the stronger/elevated storms.

   ...The Upper Ohio Valley and central Appalachians...
   Florence will continue a gradual weakening trend with time as it
   becomes increasingly absorbed within mid-latitude west-northwesterly
   flow.  While shear within the lowest couple of km will likely remain
   sufficient for low-level rotation, especially early in the period,
   widespread precipitation/cloud cover should once again limit
   potential for heating/destabilization across the region.  Therefore,
   with potential for stronger/cellular updrafts expected to remain
   low, any tornado potential across the area likewise appears limited,
   so as to preclude inclusion of a risk area at this time.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:     <5%     - None
   Hail:      5%     - Marginal

   ..Goss.. 09/16/2018

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