SPC AC 010509

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1109 PM CST Tue Nov 30 2021

   Valid 021200Z - 031200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   A couple of weak thunderstorms are possible near the Rio Grande
   River and higher terrain of southwest Texas, but the risk of
   thunderstorms appears negligible elsewhere across the U.S. Thursday
   through Thursday night.

   ...Discussion...
   Although a significant digging short wave impulse may suppress
   mid-level ridging across parts of the Canadian Prairies, models
   indicate that a strong, broadly anticyclonic belt of flow will
   persist in mid to upper levels, from the eastern mid-latitude
   Pacific across much of the northern tier of the U.S. through this
   period.  The leading edge of this jet is forecast to dig southeast
   of the Mid Atlantic coast, into the base of an amplifying mid-level
   trough off the northern Atlantic Seaboard, which may be accompanied
   by substantive further deepening of a surface cyclone migrating
   across southern Quebec through the lower St. Lawrence Valley.  

   At the same time, a developing perturbation, emerging from
   persistent weak mid/upper troughing in the subtropical westerlies,
   is forecast to overspread parts of the southern Rockies, Rio Grande
   River and higher terrain of southwest Texas, and adjacent southern
   Great Plains.  As this occurs, surface ridging initially
   encompassing much of the Gulf Coast and Gulf of Mexico may slowly
   weaken.  However, low-level moisture return likely will remain
   generally modest, and confined to a shallow near-surface layer
   across the lower Rio Grande Valley into portions of the southern
   Great Plains. 

   Across the higher terrain of southwest Texas into parts of the
   Edwards Plateau and Texas South Plains, NAM forecast soundings
   suggest that moisture return emanating from the subtropical eastern
   Pacific may contribute to weak destabilization by late Thursday
   afternoon into Thursday night.  Northeast of the higher terrain, it
   appears that this will be mostly after dark, above elevated
   mixed-layer air, and it remains unclear whether forcing for ascent
   will be sufficient to contribute to an appreciable risk for
   thunderstorms.  However, orographic forcing may aid the development
   of a couple of weak thunderstorms across the mountains of southwest
   Texas by Thursday evening.

   ..Kerr.. 12/01/2021

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