SPC AC 010543

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1243 AM CDT Tue Sep 01 2020

   Valid 011200Z - 021200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
   OF THE SOUTHERN PLAINS INTO THE TENNESSEE AND OHIO VALLEY REGIONS...

   ...SUMMARY...
   A few strong to severe storms capable of damaging wind gusts and
   hail will be possible over a portion of the southern Plains Tuesday.
   Other storms with a few locally strong to severe gusts will be
   possible over a portion of the Tennessee and Ohio Valleys.

   ...Synopsis...
   Shortwave trough currently moving through the Great Basin is
   expected to continue southeastward through the Four Corners and into
   the southern High Plains. As it does, it will become increasingly
   displaced from the stronger mid-level flow arcing cyclonically from
   British Columbia through the Great Lakes and into Quebec. Elsewhere,
   a modest, convectively augmented shortwave trough is expected to
   move northeastward through the OH Valley. 

   At the surface, a cold front currently extends from central IL
   southwestward through central MO and central OK into in TX Low
   Rolling Plains. Northern portions of this front may see modest
   eastward/southeastward progress today but much of the front is
   expected to remain largely in place.  

   ...Southern Plains...
   Numerous showers and thunderstorms are currently ongoing across
   central and eastern OK, just ahead of the cold front mentioned in
   the synopsis. This trends will continue into morning, with some
   modest southeastward shift in the location of the storms thereafter
   as the cold pools amalgamate. A strong downburst or two is possible
   within this cluster but the prevailing expectation is for the storms
   to remain outflow dominant. 

   Farther west, the approaching shortwave trough is expected to
   provide the lift needed for afternoon and evening thunderstorms
   across the TX Panhandle. However, destabilization will depend on the
   location and coverage of any preceding storms this morning. Even if
   the air mass is able to sufficiently destabilize, vertical shear
   will be relatively modest and overall severe coverage will likely
   remain isolated.  

   ...Mid-South into the Middle OH Valley...
   As mentioned in the synopsis, a shortwave trough is expected to move
   northeastward through the OH Valley today. This shortwave will be
   accompanied by increased southwesterly flow aloft, contributing to a
   corridor of stronger vertical shear from eastern AR into OH. Despite
   ample low-level moisture, instability along this corridor will be
   tempered by weak mid-level lapse rates. Even so, a few stronger,
   more organized updrafts capable of damaging downbursts are possible.
   A brief tornado or two is also possible.

   ...Northern MN...
   Shallow thunderstorms are anticipated ahead of a cold front expected
   to move quickly across the region this evening. Low-level moisture
   will be limited, but mid-level temperatures will be cold enough for
   modest instability. Vertical shear will also be strong. As a result,
   a few instances of sub-severe hail are possible with the strongest
   storms.

   ..Mosier/Lyons.. 09/01/2020

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