THIS AVALANCHE FORECAST EXPIRED ON December 16, 2020 @ 6:54 am
Avalanche Forecast published on December 15, 2020 @ 6:54 am
Issued by Steve Reynaud - Tahoe National Forest

Dangerous avalanche conditions continue with persistent slab and wind slab avalanche problems.  An unstable weak layer is buried in a large part of the usable terrain in our area.  CONSIDERABLE avalanche danger exists at all elevations.  Advanced route finding and decision making skills are required to avoid todays avalanche problems.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Persistent Slab
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The Dec. 11 persistent weak layer is now buried under 6 to 12'' of recent storm snow.  Many reports of loud whumpfing sounds and cracking came in yesterday across the entire forecast area.  This weak buried facet layer, that formed during our long dry spell from Nov 18 to Dec 11, is widespread below treeline and near treeline on W-NW-N-NE-E aspects. It has also been noted in isolated areas above treeline.  This persistent weak layer is showing unstable signs with the additional storm load, it may only need the added weight of a person to trigger an avalanche.  These avalanches could have wide propagation and be remotely triggered from below, above, to the side, or from any connected terrain. 

Advanced terrain management and route finding skills are required.  This persistent slab avalanche problem lives in the same terrain that also has the most snow coverage for recreation.  Utilize slopes that are well under 30 degrees in steepness and not connected to any steeper terrain.  Whumpfing sounds or cracking will be major signs of instability.  Consequences of an avalanche remain high with our shallow early season snowpack with many exposed obstacles to potentially hit.        

Avalanche Problem 2: Wind Slab
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Wind slabs developed during the recent storm in near and above treeline terrain from gale force SW winds.  Unstable wind slabs have been reported over the last 3 days with at least 1 natural avalanche occurring yesterday.  Human triggered wind slabs are expected to remain reactive today as well as cornice fall.  Where wind slab are deposited on top of the persistent weak layer, these avalanches could propagate wide, be remotely triggered, and create much larger avalanches.

Look for newly developed cornices and wind pillows towards the upper part of slopes and below ridges.  Any cracking or signs of denser snow over less dense snow in these areas will be an indication of unstable wind slab.  Cornice fall could be large triggers for avalanches today.  Managing multiple avalanche problems at all elevations will be required today.       

recent observations
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*  Unstable wind slabs have been reported over the last 3 days.  Yesterday, a natural cornice collapse and wind slab avalanche was reported from Silver Peak.

*  The Dec 11 persistent weak layer was formed by the faceting process during our extended dry period from Nov 18 through Dec 11 and is now buried 6 to 12'' below the snow surface.  This buried faceted weak layer is widespread below treeline, near treeline, and is some case above treeline on W-NW-N-NE-E aspects.  Widespread whumpfing, cracking, and unstable snowpack test results have been reported throughout the forecast region.

 

Weather and CURRENT CONDITIONS
weather summary

Calm weather is forecasted for today and most of Wednesday with seasonal temperatures and partly cloudy skies.  NE winds should remain light to moderate at the higher elevations before shifting to the SW as our next storm approaches Wednesday night.  A winter storm warning is in effect for Wednesday night through Thursday morning as a fast moving storm approaches our region.  

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 25 to 29 deg. F.
Max. temperature: 29 to 30 deg. F.
Average ridgetop wind direction: NE
Average ridgetop wind speed: 20 to 30 mph
Maximum ridgetop wind gust: 42 mph
New snowfall: 0 inches
Total snow depth: 22 to 29 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 37 to 42. deg. F. 21 to 27. deg. F. 39 to 44. deg. F.
Mid Slope Winds: North 10 to 15 mph in the morning becoming west. Gusts to 25 mph. West around 10 mph. Light winds becoming west 10 to 20 mph with gusts up to 30 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Partly cloudy. Snow levels 7000 feet. Chance of precipitation is 0%. Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 33 to 39. deg. F. 20 to 26. deg. F. 35 to 41. deg. F.
Ridge Top Winds: Northeast 15 to 30 mph becoming west in the afternoon. Gusts to 50 mph in the morning. West 15 to 25 mph with gusts up to 40 mph. Southwest 15 to 25 mph. Gusts up to 40 mph increasing to 60 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258