SPC AC 191650

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1050 AM CST Sun Dec 19 2021

   Valid 201200Z - 211200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk of severe thunderstorms appears negligible across the U.S.
   Monday through Monday night.

   ...Synopsis...
   Mid/upper flow across the Pacific has become highly amplified, and
   models suggest that embedded blocking ridging will become
   increasingly prominent in the mid-latitudes near 160-170 W
   longitude.  To the east of this ridge, a broad low, with a deep
   embedded center, is forecast to evolve offshore of the Pacific
   coast, with downstream ridging building along an axis from the
   subtropical eastern Pacific through much of the Colorado Valley/Four
   Corners states vicinity.

   As this occurs, models indicate that relatively amplified mid/upper
   troughing farther downstream will gradually dig east-southeast of
   the southern Great Plains/lower Rio Grande Valley vicinity, through
   much of the western Gulf Coast and Gulf of Mexico Monday through
   Monday night.  Well south of a more zonal and progressive belt of
   westerlies curving in broadly cyclonic fashion across the Canadian
   Rockies through the Canadian Maritimes and New England, there
   remains substantive spread concerning this perturbation and
   potential related wave development along a stalling surface frontal
   zone across the Gulf of Mexico.  However, in the wake of this recent
   frontal intrusion, generally dry and/or stable conditions appear
   likely to prevail across much of the nation, with little risk for
   thunderstorm activity.

   ...Florida...
   An influx of drier boundary-layer air across much of northern
   Florida and the interior peninsula, beneath lingering relatively
   warm and weakly capping layers aloft seems likely to minimize the
   risk for thunderstorm development through much of the period.

   Even the various model output depicting a more progressive mid-level
   wave, with stronger surface cyclogenesis approaching the Florida
   Peninsula late Monday night, suggest that an appreciable risk for
   thunderstorms may not develop into Gulf coastal areas until close to
   12Z Tuesday.  Given the strengthening of the lower/mid tropospheric
   wind fields in these solutions, however, destabilization could
   become sufficient to support supercells and an associated risk for
   severe weather.  Trends will need to be monitored, but, at this
   time, severe weather probabilities still appear negligible through
   this period.

   Otherwise, aside from the warm sector of the developing surface low
   over the eastern Gulf of Mexico, models suggest that forcing for
   ascent in a downstream warm advection regime east of northern
   Florida coastal areas will provide the primary focus for
   thunderstorm development--mostly Monday night.

   ..Kerr.. 12/19/2021

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