SPC AC 010559

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1159 PM CST Tue Nov 30 2021

   Valid 031200Z - 041200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk of severe thunderstorms appears negligible across the U.S.
   Friday through Friday night, but a low probability of thunderstorms
   may develop across the southern Great Plains.

   ...Discussion...
   One prominent branch of increasingly split westerlies, emanating
   from the mid-latitude Pacific, appears likely to remain broadly
   anticyclonic across the western Canadian/U.S. border into the
   northern U.S. Great Plains and Mississippi Valley through this
   period.  However, mid/upper flow across the Great Lakes region may
   trend at least broadly cyclonic, in response to a significant short
   wave perturbation digging southeast of the Canadian Prairies.  It
   appears that this will be accompanied by much more modest surface
   cyclogenesis than the preceding short wave impulse, but models
   suggest that a more prominent cold surface ridge will build
   southeast of the northern Rockies, through much of the northern into
   central Great Plains and upper Mississippi Valley by 12Z Saturday.

   At the same time, a series of short wave perturbations is forecast
   to continue to develop eastward across parts of the Southwest into
   the Gulf Coast states, within a weak branch of westerlies emanating
   from the subtropical eastern Pacific.  Across parts of the southern
   Great Plains, elevated moisture return of subtropical Pacific origin
   will be coupled with moistening from the Gulf of Mexico, on
   southerly low-level return flow.  Models continue to suggest that
   the Gulf moisture return may be mostly confined to a relatively
   shallow near-surface layer, beneath relatively warm and capping
   elevated mixed-layer air.  However, within weak surface troughing
   ahead of the southward advancing cold front, and perhaps within
   lower/mid-tropospheric warm advection to the northeast of a weak
   frontal wave by late Friday night, areas of destabilization and lift
   may become sufficient to support isolated to widely scattered weak
   thunderstorm activity.

   ..Kerr.. 12/01/2021

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