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 25, 2009:

February 25, 2009 at 7:58 am

Near and above treeline, avalanche danger is MODERATE on N-NE aspects, 35 degrees and steeper. Pockets of MODERATE danger also exist on adjacent aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on N-NE aspects, 35 degrees and steeper between 7,400' and 8,700'.

Forecast Discussion:

A weak weather system is passing through the forecast area this morning. Snowfall associated with this system is expected in the form of isolated showers, focused mainly along the Sierra Crest with minimal accumulation. Air temperatures in the upper 20s to low 30s this morning are expected to climb slightly into the upper 20s and mid 30s today. Ridgetop winds remain strong out of the southwest this morning, but are expected to decrease to moderate in speed this afternoon.

Yesterday, natural avalanche activity was reported from Donner Peak (Donner Summit area) on a NE aspect at approx 7,500' and on the far SE ridge of Tamarack Peak (Mount Rose area) on a NE aspect at approximately 9,200'. Both avalanches occurred during the predawn hours. No additional avalanche activity was reported to have occurred during the day. With clear skies and good visibility for the first time in days, numerous crowns from recent avalanches were visible in the backcountry on NW-N-NE-E aspects at all elevations.

Blowing snow was observed throughout the day in above treeline areas on the higher peaks. Observations made on Maggie's Peak (Desolation Wilderness Area) indicate that the snowpack below 7,500' that was effected by rain on Sunday and Monday has begun the process of refreezing and stabilizing. New snow above 7,500' has begun to stabilize as well. Stability tests performed on a 34 degree N aspect at 8,000' indicated that fracture propagation remains possible on the persistent weak layer of faceted snow crystals just above the January 22-23 rain crust.

Today, two main avalanche concerns exist. This first is continued deep slab instability associated with the crust / facet layer located 3 to 8 feet deep within the snowpack at the January 22-23 rain crust. Failure of this layer is most likely to occur near the Sierra Crest in complex terrain on steep N-NE aspects between 7,400' and 8,700'. Becoming caught in an avalanche that fails this deep within the snowpack will continue to have severe consequences.

The second avalanche concern is smaller slabs of wind loaded snow that formed from blowing snow yesterday and small amounts of new snow overnight. These slabs will be found near and above treeline on NW-N-NE-E aspects. Human triggered avalanches involving this weak layer within the upper portion of the snowpack may be large enough to bury a person, especially if a terrain trap is involved or if the initial avalanche is able to trigger additional failure deeper within the snowpack.


The bottom line:

Near and above treeline, avalanche danger is MODERATE on N-NE aspects, 35 degrees and steeper. Pockets of MODERATE danger also exist on adjacent aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE on N-NE aspects, 35 degrees and steeper between 7,400' and 8,700'.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature: 24 deg. F.
Max. temperature in the last 24 hours: 30 to 32 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 58 mph
Maximum wind gust in the last 24 hours: 86 mph
New snowfall in the last 24 hours: 0 to trace inches
Total snow depth: 121 inches

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

For 7000-8000 ft:
  Wednesday: Wednesday Night: Thursday:
Weather: Mostly cloudy skies with a slight chance of snow showers in the morning. Scattered snow showers in the afternoon. Cloudy skies with snow likely. Snow likely in the morning, then partly cloudy with a chance of snow showers in the afternoon.
Temperatures: 31 to 38 deg. F. 25 to 30 deg. F. 27 to 34 deg. F.
Wind direction: SW SW SW
Wind speed: 10 to 20 mph with gusts to 30 mph. 10 to 15 mph with gusts to 25 mph, increasing to 15 to 25 mph with gusts to 50 mph after midnight. 20 to 30 mph with gusts to 55 mph.
Expected snowfall: 0 to trace in. 2 to 6 in. 3 to 8 in.

For 8000-9000 ft:
  Wednesday: Wednesday Night: Thursday:
Weather: Mostly cloudy skies with a slight chance of snow showers in the morning. Scattered snow showers in the afternoon. Cloudy skies with snow likely. Snow likely in the morning, then partly cloudy with a chance of snow showers in the afternoon.
Temperatures: 25 to 30 deg. F. 20 to 25 deg. F. 24 to 30 deg. F.
Wind direction: SW SW SW
Wind speed: 25 to 35 mph with gusts to 60 mph, decreasing to 20 to 30 mph with gusts to 45 mph in the afternoon. 25 to 40 mph with gusts to 60 mph, increasing to 40 to 55 mph with gusts to 90 mph after midnight. 45 to 65 mph with gusts to 100 mph.
Expected snowfall: 0 to trace in. 2 to 6 in. 3 to 8 in.