SPC AC 061249

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Thu Aug 06 2020

   Valid 061300Z - 071200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS MT TO THE
   SOUTHERN GREAT PLAINS AND THE SOUTHEAST...

   ...SUMMARY...
   A broad area of mainly isolated severe storms is expected this
   afternoon and evening from Montana to the southern Great Plains.
   Localized damaging winds should also occur across parts of the
   Southeast.

   ...Synopsis...
   A mid-level anticyclone will remain centered over the TX
   Trans-Pecos, while a shortwave trough impinges on the Canadian
   Rockies and northwest MT by early Friday. In between these features,
   several MCVs will predominately drift east across parts of the
   central/southern Rockies and Great Plains.

   ...Eastern WY, western SD, and the NE Panhandle...
   A subtle mid-level impulse evident in water vapor imagery over
   western WY should instigate isolated to scattered thunderstorms 
   over the Big Horns and along a lee trough across eastern WY this
   afternoon. While modest mid and upper-level winds will be a limiting
   factor, a veering wind profile with height in the low levels should
   contribute to 25-30 kt effective shear. This should yield a
   predominant cluster mode with activity spreading east into parts of
   western SD and the NE Panhandle this evening. With a plume of
   moderate buoyancy east of WY, a relative increase in severe wind
   potential may become realized. But with uncertainty in the
   latitudinal extent of the threat, will defer to later outlooks for a
   possible cat 2/SLGT risk upgrade.

   ...OK and southern KS...
   Convection is ongoing across southwest KS into far northwest OK in a
   zone of weak low-level warm advection that is forecast to slowly
   subside this morning. Residual cloud cover will likely yield
   pronounced differential heating across a developing warm front as
   surface temperatures become hot in western OK (well into the 90s). A
   subtle mid-level speed max within confluent westerly flow should lie
   along the KS/OK border area this afternoon. 

   Renewed convective development is possible this afternoon within the
   remnants of this morning's convection near/northeast of the surface
   warm front, a scenario simulated by the 00Z NSSL-ARW, 11Z
   HRRR-operational, and 10Z HRRR-parallel. Given a mean-mixing ratio
   around 15 g/kg per the 12Z OUN sounding, large buoyancy would foster
   a risk for at least isolated severe wind and hail.

   ...MT...
   Stronger mid-level flow attendant to the shortwave trough will
   largely lag behind an eastward-moving cold front. In addition, with
   surface dew points in the 40s across much of the state at present,
   buoyancy should remain weak despite robust daytime heating. A deep,
   well-mixed thermodynamic profile should support isolated severe wind
   gusts within isolated to scattered high-based convection. 

   ...Southeast...
   20-30 kt 500-mb southwesterlies will persist downstream of a
   low-amplitude mid-level trough over the TN Valley. While one cluster
   of strong storms has recently departed the NJ/DE coast, several more
   clusters will develop this afternoon from the central and southern
   Appalachians to the coastal plain. With thunderstorm coverage
   becoming scattered to widespread, isolated damaging winds are
   expected over much of the region.

   ..Grams/Jewell.. 08/06/2020

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