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 November 25, 2010:


November 25, 2010 at 6:36 am

Isolated pockets of MODERATE avalanche danger remain on the most heavily wind-loaded N-NE-E-SE aspects and on newly wind-loaded NW-W-SW-S-SE aspects near and above treeline on slopes steeper than 35 degrees. Below treeline the avalanche danger is LOW.


Forecast Discussion:


The high pressure ridge over the forecast area should bring warmer temperatures, mostly clear skies, and north to east winds to the mountains today. This ridge should begin moving eastward as a low pressure pushes toward the region. By tonight a few thin clouds should start to develop, and the winds should shift to the south and west ahead of this low. The clouds and southwest winds should increase tomorrow afternoon and evening as the low moves closer.

Observations:

Calm, sunny, mild weather yesterday allowed the snowpack to continue settling. Evidence of a few recent avalanches remained on wind-loaded, N-NE-E aspects above treeline between Red Lake Peak and Stevens Peak. These slides most likely occurred naturally during the storm on Tuesday. One small, isolated wind slab did release in response to a skier's weight on Red Lake Peak during the day yesterday. This slide was about 25 ft wide and 1 ft deep (photos and more info). In most other areas on Red Lake Peak and on Tamarack Peak in the Mt. Rose area observations showed a mostly stable snowpack. Hand pits and layer bonding tests indicated that layers in the snowpack continue to form bonds within themselves and with other layers. On Tamarack Peak some minor cracking did occur on a small wind-loaded, E facing, 33 degree test slope near treeline. Ski cuts on other similar test slopes did not display any signs of instability. By late afternoon a noticeable sun crust had formed on southerly aspects up to 8500' in the Mt. Rose area and in the Carson Pass area.

Avalanche Concerns:

Some wind slabs that formed during Tuesday's storm could still fail in response to the added weight of a person.  These fragile wind slabs have become more and more isolated as the snowpack continues to settle and bond. The best places for these isolated pockets of instability will be on the most wind-loaded N-NE-E aspects and cross-loaded SE aspects near and above treeline on slopes steeper than 35 degrees. Steep, wind-loaded, complex terrain such as hanging snowfields or couloirs may also hold some of these fragile wind slabs. Expect any cornices formed during the storm to remain sensitive to human-triggering. The east and northeast winds did increase yesterday evening. The forecast calls for them to continue today. They should have started to transport enough snow from the N-NE-E aspects onto the SE-S-SW-W aspects to form new, small wind slabs. These new wind slabs could also be sensitive to human-triggering today.


The bottom line:

Isolated pockets of MODERATE avalanche danger remain on the most heavily wind-loaded N-NE-E-SE aspects and on newly wind-loaded NW-W-SW-S-SE aspects near and above treeline on slopes steeper than 35 degrees. Below treeline the avalanche danger is LOW.


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 10 deg. F.
Max. temperature in the last 24 hours: 15 deg. F.
Average wind direction during the last 24 hours: Calm till yesterday evening becoming ENE overnight
Average wind speed during the last 24 hours: Calm till yesterday evening increasing to 30-35 mph
Maximum wind gust in the last 24 hours: 48 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 44-54 inches

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

For 7000-8000 ft:

  Thursday: Thursday Night: Friday:
Weather: Sunny this morning becoming partly cloudy this afternoon. Partly cloudy Partly cloudy
Temperatures: 28-35 deg. F. 14-20 deg. F. 33-40 deg. F.
Wind direction: East Variable Southwest
Wind speed: 10 mph Light 10 mph
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Thursday: Thursday Night: Friday:
Weather: Sunny this morning becoming partly cloudy this afternoon. Partly cloudy Partly cloudy
Temperatures: 33-39 deg. F. 18-25 deg. F. 32-39 deg. F.
Wind direction: East Southeast to Southwest Southwest
Wind speed: 15-25 mph with gusts to 45 mph 15-20 mph with gusts to 40 mph decreasing to 10-15 mph with gusts to 30 mph after midnight 15-25 mph with gusts to 40 mph
Expected snowfall: O in. O in. O in.