Storm Prediction Center Dec 13, 2021 1630 UTC Day 1 Convective Outlook

Dec 13, 2021 1630 UTC Day 1 Convective Outlook

Updated: Mon Dec 13 16:20:50 UTC 2021 (

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Probabilistic to Categorical Outlook Conversion Table

Categorical Graphic

Day 1 Risk	Area (sq. mi.)	Area Pop.	Some Larger Population Centers in Risk Area
No Risk Areas Forecast

Probabilistic Tornado Graphic

20211213 1630 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

20211213 1630 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

20211213 1630 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 131620

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1020 AM CST Mon Dec 13 2021

   Valid 131630Z - 141200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   A few thunderstorms will be possible across the eastern Florida
   Peninsula, and over parts of the West Coast and northern California.

   ...Northern CA...
   Upper pattern will amplify today across the western CONUS as heights
   rise from the central High Plains into British Columbia ahead of a
   strong shortwave trough approaching the northern/central CA coast.
   Surface low associated with this shortwave trough is currently
   centered just off the central/southern OR coast. This low is
   expected to deepen throughout the day while gradually moving
   north-northeastward. A strongly forced frontal band associated with
   this system is forecast to move southeastward throughout the day,
   moving first through southwest/south-central OR and adjacent far
   northern CA later this morning before then moving through more of
   northern CA and the Bay Area later this afternoon/evening. 

   Buoyancy will be modest and relatively shallow, keeping updraft
   depth limited and likely precluding anything but isolated lightning
   flashes. Even with the limited buoyancy and updraft depth, strong
   low-level flow accompanying the frontal band could contribute to
   storm-scale cyclonic shear/rotation. This is particularly true
   across portions of Sacramento Valley east of the Bay Area, where
   channeled low-level flow will be more southerly, contributing to
   strong low-level vertical shear. Even so, given the weak buoyancy
   and limited low-level moisture, the overall threat appears too
   low/conditional to outlook any areas.

   ...Elsewhere...
   Dry and stable conditions are anticipated elsewhere across the
   majority of the central and eastern CONUS. The only exception is
   over the east-central FL coast, where a few westward moving
   thunderstorms may reach the coast.

   ..Mosier/Wendt.. 12/13/2021

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