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 27, 2009:

February 27, 2009 at 7:49 am

Near and above treeline, avalanche danger is LOW with pockets of MODERATE danger on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with pockets of MODERATE danger on N-NE aspects, 37 degrees and steeper between 7,400' and 8,700'. Avalanches may be more difficult to trigger today, but are likely to be large in size with potential consequences severe.

Forecast Discussion:

A short lived period of high pressure is over the forecast area this morning. Expect sunny skies today before cloud cover begins to increase tonight and tomorrow ahead of an approaching storm system. Ridgetop winds remain out of the southwest this morning, but decreased to moderate in speed overnight. Air temperatures in the upper teens and 20s this morning are expected to rise into the low to mid 30s today in most locations.

No new avalanche activity has been reported from the backcountry in the past 72 hours. A significant number of crowns and debris fields are visible in the backcountry from the past two avalanche cycles. Yesterday, observations made on Silver Peak (North of Squaw Peak) revealed large amounts of blowing snow and hard slab formation on the majority of aspects in the area. Stability tests performed at 8,000' on a N aspect, 32 degree slope indicated that layer bonding of the surface hard slab to the snow below was poor. Observations made on Incline Lake Peak (Mount Rose Area) at 9,300' on a N aspect, 31 degree slope indicated similar poor bonding of surface slab to the snow below. Of note, stability tests targeting fracture propagation potential indicated that propagation was likely in this area on a layer of faceted crystals at mid height, or about 3 feet deep within the snowpack. This is the first indications of potential deep slab instability in this area.

Today, avalanches may be more difficult to trigger, but potential consequences remain severe. At this time, avalanche concerns are twofold. The first avalanche concern is hard slabs that have formed from blowing snow and small amounts of new snow over the past 60 hours. These slabs will be found near and above treeline on NW-N-NE-E-SE aspects. An avalanche with hard slab characteristics may have increased destructive potential for its relative size.

The second concern is continued deep slab instability associated with the crust / facet layer located 3 to 8 feet deep within the snowpack at the top of 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'. While avalanche activity involving this layer as quieted down over the past several days, the lurking persistent weak layer remains. Some evidence is beginning to indicate that deep slab instability may also exist in the Mount Rose area on N aspects above 9,000'. Be weary of steep complex terrain that lies within these parameters.


The bottom line:

Near and above treeline, avalanche danger is LOW with pockets of MODERATE danger on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with pockets of MODERATE danger on N-NE aspects, 37 degrees and steeper between 7,400' and 8,700'. Avalanches may be more difficult to trigger today, but are likely to be large in size with potential consequences severe.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature: 17 deg. F.
Max. temperature in the last 24 hours: 26 to 29 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 53 mph
Maximum wind gust in the last 24 hours: 104 mph
New snowfall in the last 24 hours: 1 to 2 inches
Total snow depth: 127 inches

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

For 7000-8000 ft:
  Friday: Friday Night: Saturday:
Weather: Partly cloudy skies. Mostly cloudy skies. Mostly cloudy skies.
Temperatures: 31 to 38 deg. F. 21 to 27 deg. F. 36 to 43 deg. F.
Wind direction: SW SW S
Wind speed: 10 to 15 mph with gusts to 25 mph. 10 to 15 mph. Around 10 mph, increasing to 15 to 25 mph with gusts to 35 mph in the afternoon.
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:
  Friday: Friday Night: Saturday:
Weather: Partly cloudy skies. Mostly cloudy skies. Mostly cloudy skies.
Temperatures: 30 to 36 deg. F. 21 to 29 deg. F. 33 to 40 deg. F.
Wind direction: SW SW S
Wind speed: 15 to 25 mph with gusts to 40 mph. 15 to 25 mph with gusts to 35 mph. 20 to 35 mph with gusts to 55 mph.
Expected snowfall: O in. O in. O in.