Dec 25, 2021 1300 UTC Day 1 Convective Outlook
Updated: Sat Dec 25 12:35:02 UTC 2021 (20211225 1300Z Day 1 shapefile | 20211225 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20211225 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Tornado Graphic
20211225 1300 UTC Day 1 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 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20211225 1300 UTC Day 1 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 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Large Hail Graphic
20211225 1300 UTC Day 1 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 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
   SPC AC 251235

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0635 AM CST Sat Dec 25 2021

   Valid 251300Z - 261200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Isolated thunderstorms will be possible along the Pacific Coast and
   in portions of the Ohio Valley today.

   ...Synopsis/Discussion...
   Mean large-scale troughing will persist over the West Coast and
   vicinity, as a series of nearly phased shortwave troughs moves
   ashore from CA-WA tonight.  Associated cold air aloft, atop the
   Pacific marine layer, will foster suitably steep low/middle-level
   lapse rates and weak but sufficient buoyancy for isolated/episodic
   thunder near the coast.  Warm/moist advection into parts of the CA
   Central Valley into the western Sierra this afternoon into early
   evening will support isolated thunder potential in an extensive,
   southeastward-shifting, southwest/northeast-oriented precip band,
   with 50-150 J/kg MLCAPE and up to 250 J/kg MUCAPE possible, despite
   cool surface temperatures.

   A downstream shortwave trough was evident in moisture-channel
   imagery over the IL/IN area and lower Ohio Valley with a lobe
   eastward over Lake Erie. This perturbation is expected to move 
   eastward through the day, the offshore from the Mid-Atlantic and New
   England between 06-12Z.  Ahead of this perturbation, streaky/
   episodic lightning has been detected in the western parts of an
   extensive precip plume that extends into a winter-weather regime in
   NY/New England.  This activity is supported by a broad regime of
   elevated, low-level UVV/warm advection, moisture transport and weak
   destabilization.  Despite smallness of both CAPE and CAPE density,
   extension of the upper part of 50-200 J/kg MUCAPE into icing layers
   suitable for lightning generation will support sporadic thunder this
   morning toward the mid/upper Ohio Valley.  Given 50-60-kt LLJ winds
   just above the surface the next few hours, isolated strong gusts may
   occur where downdrafts can transport enough momentum to the surface.

   ..Edwards.. 12/25/2021

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