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 March 5, 2009:


March 5, 2009 at 7:53 am

Near and above treeline, avalanche danger is MODERATE on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW.


Forecast Discussion:


A mix of sun and afternoon snow showers is expected today as moisture lingers over the forecast area. The storm system that affected the forecast area over the past few days left behind a total of 3 to 6 feet of new snow. Air temperatures this morning are in the teens at nearly all locations. Air temperatures are expected to rise into the 20s and low 30s today. Ridgetop winds remain moderate in speed from the southwest.

Yesterday, observations made on Jake's Peak (West Shore Tahoe area) indicated that a significant period of snowpack instability had occurred during the early morning hours. Evidence of widespread natural avalanche activity was visible below treeline between 7,000' and 9,000' on N-NE aspects steeper than 35 degrees. The instability occurred on a very subtle density change within the new snow with slab failure 8 inches deep in the snowpack. A couple inches of new snow covered the crowns and debris (photo 1, photo 2). This instability was later human triggered by the first group setting a skin track up the peak, with significant cracking and very small slab avalanches observed (photo 1, photo 2). This instability had stabilized by the afternoon hours. At the top of the peak in a near treeline area, a 2 foot crown and avalanche debris were visible from overnight natural avalanche activity at 9,380 on a wind loaded NE aspect, 37 degree slope. Light to moderate blowing snow was observed over ridgetops throughout the day, contributing to continued slab formation in wind loaded areas.

Snowpit data and stability tests taken on Jake's Peak at 7,600' on a NE aspect, 25 degree slope indicated that the entire height of the storm snow was rapidly bonding. Some minor faceting was observed above the March 1-2 rain crust at the base of the storm snow, but a significant weak layer had not yet formed. Snotel data from around the forecast area indicates that around 6 inches of settlement has occurred over the past 24 hours.

Today, human triggered avalanches remain possible near and above treeline in recently wind loaded areas, mainly on steep NW-N-NE-E-SE aspects. Continued SW winds and drifting snow have kept loading in these areas active. Instabilities that were observed yesterday in below treeline areas are expected to have stabilized. The newly formed rain crust that exists up to around 8,000' is the focus area of concern for developing instability over the next few days. We plan to watch this layer closely for developing faceted crystals and possible weak layer formation that could create another round of deep slab instability in the coming days. Some minor warming instability may occur today, especially in sun exposed areas below 7,500'. Roller balls created by snow falling from rocks and trees is the expected extent of warming instability for today.


The bottom line:

Near and above treeline, avalanche danger is MODERATE on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 13 deg. F.
Max. temperature in the last 24 hours: 23 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 30 mph
Maximum wind gust in the last 24 hours: 50 mph
New snowfall in the last 24 hours: 2 to 4 inches
Total snow depth: 164 inches

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

For 7000-8000 ft:

  Thursday: Thursday Night: Friday:
Weather: Partly cloudy skies in the morning, becoming mostly cloudy with isolated snow showers in the afternoon. Cloudy skies with scattered snow showers. Mostly cloudy skies with scattered snow showers.
Temperatures: 29 to 35 deg. F. 8 to 15 deg. F. 27 to 33 deg. F.
Wind direction: SW W NW
Wind speed: Around 10 mph. 15 to 25 mph with gusts to 35 mph. 10 to 20 mph with gusts to 35 mph.
Expected snowfall: 0 to trace in. Trace to 1 in. Trace in.

For 8000-9000 ft:

  Thursday: Thursday Night: Friday:
Weather: Partly cloudy skies in the morning, becoming mostly cloudy with isolated snow showers in the afternoon. Cloudy skies with scattered snow showers. Mostly cloudy skies with scattered snow showers.
Temperatures: 20 to 28 deg. F. 4 to 11 deg. F. 22 to 28 deg. F.
Wind direction: SW W NW
Wind speed: Around 10 mph. 20 to 30 mph with gusts to 65 mph. 20 to 30 mph with gusts to 55 mph.
Expected snowfall: 0 to trace in. Trace to 1 in. Trace in.