SPC AC 201724

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1224 PM CDT Wed Oct 20 2021

   Valid 211200Z - 221200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE OHIO/TENNESSEE VALLEYS INTO THE CENTRAL/SOUTHERN
   APPALACHIANS...AND WEST TEXAS...

   ...SUMMARY...
   Showers and storms with isolated strong to damaging wind gusts will
   be possible Thursday across parts of the Ohio/Tennessee Valleys into
   the central/southern Appalachians. Isolated storms capable of
   marginally severe hail and strong gusts may also occur over a small
   portion of west Texas.

   ...Ohio/Tennessee Valleys into the Central/Southern Appalachians...
   An upper trough/low should move quickly eastward across the Great
   Lakes and Midwest through the day on Thursday. An attendant cold
   front will sweep eastward across these regions, much of the OH/TN
   Valleys, and into the southern/central Appalachians by Thursday
   evening. Limited low-level moisture, with surface dewpoints
   generally in the mid 50s to low 60s, is forecast to return northward
   ahead of the front. Modest diurnal heating, poor lapse rates, and
   cloud cover will likely limit how much boundary-layer instability
   can develop Thursday afternoon, particularly across the OH Valley
   and central Appalachians where low-level moisture will be less.

   Even so, low-topped showers and storms should develop by early
   Thursday afternoon along much of the length of the cold front. The
   weak forecast instability coupled with fairly strong
   west-southwesterly winds at low/mid levels should support some
   threat for isolated strong to damaging wind gusts as storms spread
   eastward through the day. Slightly greater instability may be
   realized from TN southward into AL/GA, but deep-layer shear should
   be weaker across this area than in the OH Valley. This isolated wind
   threat should quickly wane early Thursday evening as convection
   encounters the higher terrain of the Appalachians and a less
   favorable thermodynamic environment.

   ...West Texas...
   At least isolated storms should develop Thursday afternoon over the
   higher terrain of the Davis and surrounding mountains in west TX as
   a weak mid-level disturbance moves over this region. Although
   low/mid-level winds are forecast to remain fairly modest, there will
   be some veering of the flow with height, and steep low/mid-level
   lapse rates should also be present. Any storms that can form in this
   regime may pose an isolated hail and strong/gusty wind threat
   through early Thursday evening.

   ...Southern Oklahoma...
   Most 12Z guidance indicates the potential for convection across
   southern OK will be rather limited Thursday night into early Friday
   morning. While a storm or two may still develop, weak instability,
   marginal deep-layer shear, and meager large-scale ascent all suggest
   the threat for anything more than small hail should remain low.

   ..Gleason.. 10/20/2021

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