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 15, 2009:


February 15, 2009 at 8:00 am

Near and above treeline, avalanche danger is CONSIDERABLE on NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE in open areas, 35 degrees and steeper.


Forecast Discussion:


Yet another storm system is impacting the forecast area this morning. This system is stronger than the storms observed over the last 9 days and is taking aim at the northern portion of the forecast area. An additional 3 to 7 inches of new snow fell over the Sierra Crest last night with the greatest accumulations observed north of Lake Tahoe. Less new snow accumulated overnight in the Mount Rose area. High intensity snowfall is expected to begin around 10 am this morning and spread south through the forecast area as the day progresses. New snow amounts of 18 to 40 inches are forecast over the next 48 hours with the greatest accumulation rates overnight into Monday. Air temperatures in the upper teens and low 20s this morning are expected to warm into the low to mid 20s today. Ridgetop winds have shifted to southwest and south overnight and increased from moderate to strong in speed.

Yesterday, human triggered slab avalanches were widespread both above and below treeline. Intentional and unintentional skier triggered avalanches were reported from Becker Peak (Echo Summit area) photo, Silver Peak (North of Squaw peak) photo 1, photo 2, Deep Creek (North of Squaw Peak), and Carpenter Peak (Independence Lake area) photo 1, photo 2. An isolated natural avalanche was reported at the head of Deep Creek drainage. All avalanches that occurred were on N-NE-E aspects on slopes 35 degrees and steeper. Avalanches that occurred on Becker, Silver, and in Deep Creek were in wind loaded or wind affected areas with the failure layer at the base of the new snow that fell overnight February 13-14. Crown heights measured 10 inches to 2 feet. On Carpenter Ridge, avalanches failed on the rain crust / facet layer at the interface of the January 22-23 rain crust and the February 6 storm snow. Crown heights measured 3 to 6 feet. All reported avalanches were size D2, large enough to bury a person.

Today, continued instability within the snowpack will allow human triggered avalanches to continue, mainly above 7,000' on NW-N-NE-E aspects that are 35 degrees and steeper. The threat of isolated natural avalanches remains possible today, especially after the onset of high intensity snowfall later this morning. Snowpack failure within the recent storm snow and on the faceted snow crystals just above the January 22-23 rain crust is expect to continue. Ridgetop winds that have shifted and increased in speed during the overnight hours are expected to have allowed wind loading to continue and further enhanced slab formation in lee areas. The ability of humans to trigger avalanches may be more difficult today than yesterday, but the consequences of becoming caught in an avalanche will remain high. The greatest areas of snowpack instability are expected to continue to occur along the Sierra Crest where the greatest snowfall amounts have occurred over the past 9 days.


The bottom line:

Near and above treeline, avalanche danger is CONSIDERABLE on NW-N-NE-E aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE in open areas, 35 degrees and steeper.


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: 19 deg. F.
Average wind direction during the last 24 hours: Southwest shifting to south.
Average wind speed during the last 24 hours: 54 mph
Maximum wind gust in the last 24 hours: 97 mph
New snowfall in the last 24 hours: 3 to 7 inches
Total snow depth: 104 inches

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

For 7000-8000 ft:

  Sunday: Sunday Night: Monday:
Weather: Cloudy skies with snow. Cloudy skies with snow. Cloudy skies with snow.
Temperatures: 22 to 29 deg. F. 12 to 19 deg. F. 21 to 28 deg. F.
Wind direction: S S S
Wind speed: 20 to 30 mph with gusts to 50 mph 20 to 30 mph with gusts to 50 mph 15 to 25 mph with gusts to 40 mph
Expected snowfall: 4 to 8 in. 4 to 8 in. 6 to 12 in.

For 8000-9000 ft:

  Sunday: Sunday Night: Monday:
Weather: Cloudy skies with snow. Cloudy skies with snow. Cloudy skies with snow.
Temperatures: 20 to 25 deg. F. 10 to 17 deg. F. 17 to 24 deg. F.
Wind direction: S S S shifting to SW in the afternoon
Wind speed: 40 to 60 mph with gusts 80 to 100 mph 40 to 60 mph with gusts 80 to 100 mph 30 to 50 mph with gusts 70 to 90 mph
Expected snowfall: 4 to 8 in. 4 to 8 in. 8 to 14 in.