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 7, 2009:


March 7, 2009 at 7:51 am

Near and above treeline on open, wind-loaded slopes 35 degrees and steeper, pockets of MODERATE avalanche danger exist on SE-S-SW-W-NW aspects. Below treeline, avalanche danger is LOW.


Forecast Discussion:


Sunny skies and warmer temperatures should prevail over the forecast area today due to a small high-pressure ridge. The winds shifted to the north and east last night around 8pm. These winds have averaged between 35-45 mph. They should decrease slightly today but continue from the north and east until a cold front starts to push this ridge away tomorrow afternoon. This cold front should bring clouds, strong southwest winds, colder temperatures, and a slight chance of snow starting late tomorrow.

Yesterday, observations on Sawtooth Ridge west of Northstar and on Mt. Rose showed cold, soft snow on the N-NE aspects. A dusting of new snow on top of melt / freeze crusts existed on the E-SE-S-SW-W aspects up to 8800'. These crusts were breakable in some areas and supportable in others. A mix of wind-affected, hard snow surfaces and patches of soft snow existed on the NW aspects. Snowpit tests as well as hasty tests like hand pits, ski cuts, weighting test slopes, and cornice tests all indicated a stable snowpack in most areas. Some small cracking and cornice failure occurred due to a skier's weight near the ridgelines above 9000' on Mt. Rose due to recent wind loading.

The first avalanche concern today will be new wind slabs formed by the strong north and east winds. Near and above treeline, these winds will move the light, soft snow from the open, exposed N-NE-E aspects onto the S-SW-W aspects. Some wind slabs could also form on cross-loaded slopes on SE and NW aspects. The wind slabs formed by this new loading will be sitting on a mix of crusts, light snow, and wind-scoured surfaces. Triggering avalanches on these new wind slabs should be possible for people moving across them today. Use clues like blowing snow, cornices, ripples, and other wind features to determine where wind loading exists and use extra caution around those slopes.

The second avalanche concern will result from increased temperatures and sunshine weakening the snow on the sun-exposed SE-S-SW-W aspects. The cold north and east winds and the gradual exposure to the sun over the last few days should help limit this instability in most areas. Roller-balls, small point-release sluffs, and pinwheels should comprise most of this instability today. These should not be large enough to bury a person but could knock someone off balance. This weakening of the snow due to sun and warmth will also work in concert with the new wind loading near and above treeline. The snow that the wind moves onto the sun-exposed aspects has sat in the shade on northerly aspects for the last few days. The sun and warm air will have more of a weakening affect on this cold snow making the wind slabs mentioned above more fragile.


The bottom line:

Near and above treeline on open, wind-loaded slopes 35 degrees and steeper, pockets of MODERATE avalanche danger exist on SE-S-SW-W-NW aspects. Below treeline, 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: 14 deg. F.
Max. temperature in the last 24 hours: 25 deg. F.
Average wind direction during the last 24 hours: Southwest shifting to north and east after 8pm yesterday
Average wind speed during the last 24 hours: 40 mph
Maximum wind gust in the last 24 hours: 58 mph
New snowfall in the last 24 hours: 0-2 inches
Total snow depth: 156 inches

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

For 7000-8000 ft:

  Saturday: Saturday Night: Sunday:
Weather: Sunny Clear Sunny in the morning becoming partly cloudy by the afternoon
Temperatures: 29-36 deg. F. 12-19 deg. F. 27-34 deg. F.
Wind direction: North through east West West shifting to southwest in the afternoon
Wind speed: up to 10 mph 10-15mph with gusts to 25 mph 10-15 mph with gusts to 25 mph increasing to 20-35 mph with gusts to 55 mph
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Saturday: Saturday Night: Sunday:
Weather: Sunny Clear Sunny in the morning becoming partly cloudy by the afternoon
Temperatures: 27-33 deg. F. 14-20 deg. F. 25-31 deg. F.
Wind direction: North through east Northeast Northeast shifting to southwest
Wind speed: 15-30 mph with gusts to 40 mph 20-30 mph with gusts to 35 mph increasing to gusts to 45 mph after midnight 20-30 mph with gusts to 45 mph increasing to 35-50mph with gusts to 85 mph
Expected snowfall: O in. O in. O in.