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 February 23, 2012:


February 23, 2012 at 8:00 am

The avalanche danger remains LOW for all elevations and aspects. LOW danger does not mean no danger. Continue to use normal caution when traveling in the backcountry.


Forecast Discussion:


North and east winds should bring some cooler air into the region today taht should limit daytime highs to the mid to upper 30's. The surface pressure gradient causing these winds should decrease tonight. By tomorrow the winds should shift back to the south and west. As the northerly winds cease bringing cool air into the region, temperatures should climb once again. Tomorrow's daytime highs should reach into the upper 40's and low 50's. The high pressure ridge over CA should keep skies clear through Friday.

Recent Observations:

Yesterday a wide variety of snow surface conditions existed on Tamarack Peak (photos, more info). A breakable crust has formed on the northerly aspects up to at least 9200 ft. On some slopes this crust exists at higher elevations. On the more exposed N-NE-E facing slopes, firm wind scoured surfaces prevailed. On a few of the shaded and sheltered NW-N-NE slopes above 9200 ft, softer conditions remained. Even in these areas the surface snow remained slightly more dense than the snow below it creating a "punchy" feel. People also reported breakable crusts on Rubicon and Maggie's yesterday. In the Tamarack Peak area on the more sun-exposed southerly aspects, melt-freeze conditions predominated. The warm temperatures and sunshine did manage to cause enough melting for a few inches of wet snow to form on these aspects by the afternoon. Below the surface the crust/facet combination still exists at the base of the recent snow on the NW-N-NE aspects on Tamarack Peak. Hand pits and slopes cuts on test slopes showed no signs of instability associated with this layer in this area yesterday. Extended column tests also indicated that fractures in this layer are harder to initiate, and they are also unlikely to travel though this layer. These observations match well with data collected across the forecast area over the last few days.

Today's Avalanche Concerns: Persistent Slabs

Observations over the last several days have indicated that the persistent weak layer made up of faceted snow and crusts at the base of the recent new snow has gone dormant. As this layer has adjusted to the weight of the recent snow above it, triggering avalanches has become more unlikely on near or below treeline NW-N-NE aspects. Unlikely does not mean impossible, and persistent weak layers like this one warrant extra caution. This weak layer has not gone away. It could re-awaken when more snow arrives. Continue to use caution and exercise good travel habits in order to minimize risk.

Few if any wet snow instabilities should form today due to daytime highs forecasted in the mid to upper 30's and north through easterly winds keeping the snow surface cool. Some roller balls or pinwheels may form near exposed rocks and trees on steep sun-exposed SE-S-SW facing slopes. If temperatures climb higher than forecasted today, wet snow instabilities may become more widespread and larger.


The bottom line:

The avalanche danger remains LOW for all elevations and aspects. LOW danger does not mean no danger. Continue to use normal caution when traveling in the backcountry.


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 28-33 deg. F.
Max. temperature in the last 24 hours: 46-52 deg. F.
Average wind direction during the last 24 hours: Southwest to northeast
Average wind speed during the last 24 hours: 10-20 mph
Maximum wind gust in the last 24 hours: Along the Sierra Crest: 34 mph | In the Mt Rose area: 49 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 23-33 inches

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

For 7000-8000 ft:

  Thursday: Thursday Night: Friday:
Weather: Sunny Clear Sunny
Temperatures: 35-42 deg. F. 19-26 deg. F. 43-50 deg. F.
Wind direction: Northeast East Southeast shifting to southwest in the afternoon
Wind speed: 10-15 mph with gusts to 25 mph 10-15 mph 10-15 mph with gusts to 25 mph increasing to 20-25 mph with gusts to 40 mph in the afternoon
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Thursday: Thursday Night: Friday:
Weather: Sunny Clear Sunny
Temperatures: 31-38 deg. F. 21-28 deg. F. 44-50 deg. F.
Wind direction: Northeast East Southwest
Wind speed: 20-30 mph with gusts to 50 mph decreasing to 40 mph in the afternoon 20-25 mph with gusts to 35 mph decreasing to 10-15 mph with gusts to 25 mph after midnight 20-30 mph with gusts to 35 mph increasing to 30-35 mph with gusts to 55 mph in the afternoon
Expected snowfall: O in. O in. O in.