SPC AC 261212

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0612 AM CST Sun Dec 26 2021

   Valid 261300Z - 271200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Non-severe thunderstorms are possible over parts of the Pacific
   Coast States, eastern Great Basin to central Rockies, and parts of
   the Midwest.

   ...Synopsis/Discussion...
   Large-scale mid/upper-level troughing will continue over western
   North America, anchored by a complex/elongated cyclone with centers
   over the WA Olympic Peninsula and southern Northwest Territories. 
   Associated cold air aloft will persist over coastal areas from
   northwestern CA northward, combining with the underlying moist
   marine layer to support isolated, episodic thunder potential.

   In the associated cyclonic-flow field, a series of closely spaced
   shortwave troughs and vorticity maxima are apparent in moisture-
   channel imagery from the Sierra Nevada to CO.  These perturbations
   will become somewhat more phased as they pivot northeastward toward
   the northern Great Plains and Upper Midwest, reaching portions of
   ND/MN by 12Z tomorrow.  Accompanying shots of cold air aloft and
   related steepening of lapse rates -- atop marginally favorable
   low/middle-level moisture -- will support isolated thunder potential
   during the day, shifting eastward across the eastern Great Basin to
   central Rockies.

   At the surface, 11Z analysis showed a cold front over the southern
   Mid-Atlantic region, becoming quasistationary westward over northern
   KY, southern IL, northern parts of MO/KS, and northeastern CO, into
   a regime of lee troughing over eastern WY.  By 00Z, an elongated
   cyclone should develop along the frontal zone from the Black Hills
   region to southwestern NE/northwestern KS, with the front
   strengthening somewhat in its KS/MO/IL segment.  The boundary will
   move slowly northward as a warm front tonight, reaching southern IA,
   western IL and southern IN.  To its north, elevated warm advection
   and moisture transport/advection will strengthen through the
   afternoon and especially evening.  This will occur as a cyclonically
   curved, 55-65-kt, southerly to southwesterly LLJ shifts eastward
   over the region.  200-500 J/kg MUCAPE may develop, rooted between
   700-800 mb, over the relatively stable frontal/boundary layer.  Lift
   to LFC on the elevated warm-frontal slope will support potential for
   widely scattered thunderstorms nocturnally.  Subsevere hail may
   occur briefly, but larger-hail potential appears too weak and
   conditional to warrant an outlook area.

   ..Edwards/Gleason.. 12/26/2021

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