This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory 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 advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.


This Avalanche Advisory was published on December 9, 2012:


December 9, 2012 at 7:46 am

Avalanche danger remains LOW for all elevations and aspects. Normal caution is advised. A long, unarrested, sliding fall down icy slopes leading to impact with trees or rocks is likely the greatest hazard in the backcountry today.


Forecast Discussion:


The weather system that passed to the north and east of the forecast area increased thin high cloud cover and ridgetop winds over the past 24 hours. As the system moves on, cloud cover will decrease today and winds will decrease tonight. Ridgetop winds for today will remain out of the northeast at moderate speed. Expect ridgetop gusts in the 40 to 65 mph range today. An air temperature inversion is once again in place this morning with air temperatures on the mountain valley floors in the mid 20s and air temperatures above 7,000' in the upper 20s to low 30s. Maximum daytime air temperatures are forecast to warm into the mid 30s to low 40s today for most elevations. A slight warming trend with clear skies and light to moderate northeast winds is forecast for Monday.

Recent Observations:

Observations made yesterday on Becker Peak (Echo Summit area) and on Castle Peak (Donner Summit area) revealed the continued theme of firm crusts on all aspects with some softening on southerly aspects during the mid day and early afternoon hours. The melting snow surface on southerly aspects produced 1 to 3 inches of corn snow with continued supportable snow surface conditions through the afternoon hours. This matched well with other recent observations from around the forecast area over the past three days. Supportable rain crust exists on all aspects below 9,200' and extends to above 10,000' in some areas. The rain wetted layers that existed deeper in the snowpack have now refrozen. Near crust faceting is occurring between the top two rain crusts in the snowpack. The degree to which this has occurred is highly variable around the forecast area with more development observed in the Mount Rose and Echo Summit areas and less development in the Donner Summit area (photos, pit profiles, more info).

Avalanche Concerns:

A frozen icy snowpack that has displayed a widespread lack of instability, combined with minimal solar radiation at this time of year will keep avalanche activity unlikely today. A short window of snow surface melting is expected today on southerly aspects, but not enough to cause any concerns for wet loose or wet slab avalanches. Little to no snow is available for wind transport, so new wind slab formation is unlikely today despite NE winds that are otherwise strong enough to move snow. The faceting that is occurring between the top two rain crusts in the snowpack is not an instability concern for today, but something to keep an eye on as future loading occurs.


The bottom line:

Avalanche danger remains LOW for all elevations and aspects. Normal caution is advised. A long, unarrested, sliding fall down icy slopes leading to impact with trees or rocks is likely the greatest hazard in the backcountry today.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest


Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature: 27 to 32 deg. F.
Max. temperature in the last 24 hours: 37 to 44 deg. F.
Average wind direction during the last 24 hours: NE
Average wind speed during the last 24 hours: 11 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 35 to 47 inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:

  Sunday: Sunday Night: Monday:
Weather: Partly cloudy skies, becoming sunny. Clear skies. Sunny skies.
Temperatures: 39 to 43 deg. F. 29 to 35 deg. F. 40 to 45 deg. F.
Wind direction: NE NE shifting to E after midnight. NE
Wind speed: 20 to 30 mph with gusts to 40 mph. 20 to 25 mph with gusts to 40 mph, shifting and decreasing to 10 to 15 mph with gusts to 25 mph after midnight. 10 to 15 mph with gusts to 25 mph.
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Sunday: Sunday Night: Monday:
Weather: Partly cloudy skies, becoming sunny. Clear skies. Sunny skies.
Temperatures: 35 to 40 deg. F. 29 to 34 deg. F. 36 to 42 deg. F.
Wind direction: NE NE NE
Wind speed: 35 to 45 mph with gusts to 65 mph. 35 to 40 mph with gusts to 60 mph, decreasing to 20 to 25 mph with gusts to 40 mph after midnight. 15 to 25 mph with gusts to 40 mph.
Expected snowfall: O in. O in. O in.

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