SPC AC 290728

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Sat Aug 29 2020

   Valid 311200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
   SOUTHERN PLAINS INTO THE ARKANSAS AND LOWER MISSISSIPPI VALLEYS...

   ...SUMMARY...
   Thunderstorms associated with large hail and wind damage will be
   possible across parts of the southern Plains on Monday. Wind damage
   will also be possible in parts of the Arkansas and lower Mississippi
   Valleys.

   ...Southern Plains/Arkansas and Lower Mississippi Valleys...
   Mid-level flow will become southwesterly across the southern Plains
   on Monday as an upper-level trough moves through the Intermountain
   West. At the surface, a cold front will advance quickly
   southeastward into the Texas Panhandle, western Oklahoma and
   southern Kansas on Monday, and then stall. Surface dewpoints in the
   upper 60s to lower 70s F to the southeast of the front, will result
   in moderate instability by afternoon. Thunderstorms are expected to
   develop along the front around midday with convective coverage
   increasing through the afternoon. In addition to the moderate
   instability, NAM forecast soundings in Oklahoma show 0-6 km shear of
   40 to 50 kt. This would support supercell development early in the
   event when cell coverage will be less, allowing for storms to be
   more discrete. Wind damage will also be possible with supercells.
   The wind-damage and hail threat is expected to continue through the
   evening as MCS development takes place across the southern Plains.
   There is some model spread among the solutions which introduces
   uncertainty. Differences exist in the timing of the front and amount
   of instability. At this time, it appears that the potential for a
   severe threat will be greatest in parts of the southern Plains.

   Further to the east into the Arkansas and lower Mississippi River
   Valleys, moderate instability is forecast to be in place by
   afternoon. Thunderstorms will be possible along an east-to-west
   gradient of instability from eastern Oklahoma into northern
   Mississippi. Model forecasts show 0-6 km shear of 30 to 35 kt with
   steep low-level lapse rates. This environment would support a
   wind-damage threat during the mid to late afternoon. As the southern
   Plains MCS moves into the region from the west during the late
   evening and overnight period, isolated damaging wind gusts will also
   be possible.

   ...Mid-Atlantic...
   A shortwave trough is forecast to move across the southern
   Appalachians on Monday. At the surface, a moist airmass will be in
   place from the Carolinas northward into the Mid-Atlantic. As
   moderate instability develops during the afternoon, thunderstorm
   development will be likely as large-scale ascent moves into the
   region ahead of the shortwave trough. Forecast soundings across the
   Mid-Atlantic Monday afternoon show 0-6 km shear of 30 to 35 kt along
   with steep low-level lapse rates. This should be favorable for
   marginally severe wind gusts with the stronger multicells.

   ..Broyles.. 08/29/2020

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