Dec 21, 2021 0700 UTC Day 2 Convective Outlook
Updated: Tue Dec 21 04:56:52 UTC 2021 (20211221 0700Z Day 2 shapefile | 20211221 0700Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20211221 0700 UTC Day 2 Outlook Graphic
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Tornado Graphic
20211221 0700 UTC Day 2 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 2 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20211221 0700 UTC Day 2 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 2 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Large Hail Graphic
20211221 0700 UTC Day 2 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 2 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
   SPC AC 210456

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1056 PM CST Mon Dec 20 2021

   Valid 221200Z - 231200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Isolated thunderstorms are possible near the Pacific Coast from
   northern California northward, mainly during the evening and
   overnight.

   ...Synopsis/Discussion...
   A transitional, progressive upper-air pattern will occur this
   period.  Heights will rise over most of the East following the
   offshore movement of:
   1.  A northern-stream trough -- now evident in moisture-channel
   imagery over the northern Rockies and forecast to exit New England
   between 23/00Z-23/06Z, and
   2.  A southern-stream trough -- now manifest as a compact cyclone
   over the Arklatex region -- and forecast to be just offshore of
   northern FL and the Carolinas by the start of the period.

   Low-level frontal passages related to these perturbations will
   render the air mass too dry and/or stable to support thunderstorms
   over the CONUS from the Intermountain West to the Atlantic Coast. 
   The only thunderstorm potential will be isolated near the Pacific
   Northwest coastline and over portions of northern CA.  As a synoptic
   cyclone now west of this area retrogrades and weakens, a shortwave
   trough now over southwestern AK will dig southeastward and
   strengthen.  The latter trough should move ashore between 23/06Z-
   23/12Z -- first over WA then progressively southward over OR and
   northwestern CA, given its positive tilt.

   Convection potentially deep enough for lightning will be
   predominantly in and behind a low-level frontal-lift zone related to
   and somewhat preceding the trough aloft.  MLCAPE/MUCAPE of 50-250
   J/kg is expected near the coast.  Forecast soundings also indicate
   that elevated convection in the precursory warm-advection plume,
   across north-central CA, may access weak buoyancy just below the -20
   deg C isotherm.  However, overall CAPE appears too weak to support a
   10% general thunder area.

   ..Edwards.. 12/21/2021

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   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z