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 January 25, 2012:


January 25, 2012 at 8:00 am

Near and above treeline, pockets of MODERATE avalanche danger remain on wind-loaded NW-N-NE-E aspects steeper than 35 degrees. LOW avalanche danger exists on all other aspects and elevations. Continue to evaluate slopes carefully and travel with caution in the backcountry.


Forecast Discussion:


Warm spring-like weather should return due to a high pressure ridge over the forecast area. Daytime highs above 7000 ft could reach into the upper 40's and low 50's both today and tomorrow. Moisture left over from the recent storms and from systems passing north of the region should keep some cloud cover in the skies over the Tahoe area today and tomorrow. The winds have remained light to moderate and shifted towards the west and northwest along the Sierra Crest. They should continue from the west and northwest through tomorrow and should increase tonight before starting to decrease again tomorrow. Remote sensors indicate stronger more northerly winds in the high country on the east side of the lake.

Observations:

Yesterday, observers reported more small natural avalanches on wind-loaded N-NE facing terrain in the Mt Rose area that occurred during Monday night or early Tuesday morning. Along the Sierra Crest observations on Mt. Judah (photos and more info), Becker Peak (snowpit and photos), and Round Top Peak (snowpit and photos) all showed a mostly stable snowpack. Ski cuts on steep, wind-loaded test slopes in all three of these areas did not show any signs of instability. On Becker Peak and on Mt. Judah, dropping oven-sized cornice blocks onto steep test slopes also produced no results. Snowpit tests on Round Top and on Becker Peak showed that the snowpack has almost assimilated the layers of lighter snow that formed during the storm. In these areas a much more right-side-up snowpack structure (lighter snow on top of heavier snow) now exists. By mid afternoon significant warming had caused the surface snow on the southerly aspects in all three of these areas to become wet and heavy. Some small wet surface instabilities even occurred in the Mt. Judah area below 7500 ft. On most of the northerly aspects the surface snow remained cold and dry in these areas. Reports from the Mt. Rose backcountry indicated that wet snow even existed on some northerly aspects in that area. This morning remote sensors across the forecast area showed about 5 inches of settlement has occurred during the last 24 hours.

Avalanche Concern #1 Wind slabs

As the recent snow continues to consolidate and settle, the bonds holding the snowpack together should continue to strengthen making avalanches more difficult to trigger. However, some of the wind slabs that formed during the storm may remain sensitive near and above treeline on wind-loaded NW-N-NE-E aspects today. Human triggered avalanches remain possible on these slopes.  Avalanches involving these winds slabs could entrain a significant amount of snow and pose a serious threat to anyone in their path. Some smaller new wind slabs may form on the E-SE-S-SW-W aspects as the winds shift to the northwest and northeast today and tomorrow.

Avalanche Concern #2 Wet Snow Instabilities

Some wet snow instabilities may also form today on the sun exposed southerly aspects due to warming temperatures and more sun exposure. Due to some warming since yesterday, some continued cloud cover, and the relatively low sun angles these types of instabilities should remain limited to things like pinwheels, loose surface sluffs, and other small surface instabilities. Steep open areas that face the southern half of the compass hold the best potential for this type of instability today.


The bottom line:

Near and above treeline, pockets of MODERATE avalanche danger remain on wind-loaded NW-N-NE-E aspects steeper than 35 degrees. LOW avalanche danger exists on all other aspects and elevations. Continue to evaluate slopes carefully and travel with caution 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: 32-38 deg. F.
Max. temperature in the last 24 hours: 32-38 deg. F.
Average wind direction during the last 24 hours: Along the Sierra Crest: Northwest shifting to the northeast | In the Mt Rose area: North
Average wind speed during the last 24 hours: Along the Sierra Crest: 15 mph | In the Mt Rose area: 20 mph
Maximum wind gust in the last 24 hours: Along the Sierra Crest: 32 mph | In the Mt Rose area: 60 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 25-44 inches

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

For 7000-8000 ft:

  Wednesday: Wednesday Night: Thursday:
Weather: Partly cloudy Partly cloudy Partly cloudy
Temperatures: 43-50 deg. F. 27-34 deg. F. 48-54 deg. F.
Wind direction: West West West
Wind speed: 15-20 mph with gusts to 30 mph 20-30 mph with gusts to 40 mph 20-30 mph with gusts to 45 mph decreasing to 35 mph in the afternoon
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Wednesday: Wednesday Night: Thursday:
Weather: Partly cloudy Partly cloudy Partly cloudy
Temperatures: 43-49 deg. F. 26-33 deg. F. 43-51 deg. F.
Wind direction: West West West shifting to the northwest
Wind speed: 15-25 mph with gusts to 40 mph decreasing to 30 mph in the afternoon 25-30 mph with gusts to 45 mph increasing to 35-40 mph with gusts to 60 mph after midnight 35-40 mph with gusts to 60 mph decreasing to 25-30 mph with gusts to 50 mph in the afternoon
Expected snowfall: O in. O in. O in.