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 January 1, 2011:

January 1, 2011 at 7:55 am

Near and above treeline, areas of MODERATE danger will form this morning on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with isolated pockets of MODERATE danger forming on N-NE-E aspects, 35 degrees and steeper.

Forecast Discussion:

Light snow is falling over the forecast area this morning as warmer air moves into the region. Around 1 to 3 inches of new snow has accumulated this morning. An additional 2 to 5 inches of accumulation is expected today, mainly before 11am. Air temperatures at 8,500' have been on a warming trend since since around 2 am and have risen from the mid teens to the low to mid 20s. Southwest ridgetop winds have increased to moderate in speed this morning, becoming strong enough to move snow after midnight. A second storm system is expected to impact the forecast are on Sunday, but confidence in the weather forecast for Sunday in low at this time.

Observations:

Observations made yesterday on Herlan Peak (East Shore Tahoe area) revealed very small and difficult to trigger wind slabs had formed in isolated areas on W aspects due to wind transport from recent E winds. A few small skier triggered sluffs involving moderate amounts of snow were reported from the area (photos, more info). Observations made on Silver Peak (Pole Creek area) noted widespread stable conditions in the observed areas below 8,300' on N-NE-E aspects in near and below treeline terrain. Very small cornice formations and very small wind slabs were noted on S aspects along ridgelines. These areas showed no signs of instability when weighted by a skier. Widespread settlement of the recent storm snow with cracking of settlement cones around trees was observed in both areas.

Primary Avalanche Concern: Storm snow

The combination of new snow and wind transport of old and new snow will create new slabs today. Increasing south to southwest winds last night have likely scoured and transported old snow from the small slabs and cornices that existed yesterday on S-SW-W aspects in near and above treeline terrain onto the opposite N-NE-E aspects. New snowfall and wind transport this morning will further contribute to shallow slab formation. Warming air temperatures are expected to deposit higher density snow over lower density snow, but in many areas slabs may be too shallow for any noticeable density inversions. In the more efficiently wind loaded areas near and above treeline on N-NE-E aspects, fresh slabs may reach up to 1 foot in depth today. More isolated slab formation is expected on cross loaded NW and SE aspects in near and above treeline terrain. As the morning progresses, human triggered slab avalanches will become increasingly possible. Natural avalanches will remain unlikely today. Human triggered loose snow avalanches may occur today in steep wind protected areas that receive the upper end of forecast snowfall amounts (6 to 8").


The bottom line:

Near and above treeline, areas of MODERATE danger will form this morning on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with isolated pockets of MODERATE danger forming on N-NE-E aspects, 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: 20 to 26 deg. F.
Max. temperature in the last 24 hours: 22 to 26 deg. F.
Average wind direction during the last 24 hours: East shifting to Southwest
Average wind speed during the last 24 hours: 25 mph
Maximum wind gust in the last 24 hours: 49 mph
New snowfall in the last 24 hours: 1 to 3 inches
Total snow depth: 76 to 105 inches

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

For 7000-8000 ft:
  Saturday: Saturday Night: Sunday:
Weather: Cloudy skies with snow. Cloudy skies with a chance of snow. Cloudy skies with snow.
Temperatures: 20 to 27 deg. F. 13 to 20 deg. F. 19 to 26 deg. F.
Wind direction: S S SE
Wind speed: Around 10 mph. Up to 10 mph. Up to 10 mph.
Expected snowfall: 1 to 3 in. Up to 2 in. 4 to 8 in.

For 8000-9000 ft:
  Saturday: Saturday Night: Sunday:
Weather: Cloudy skies with snow. Cloudy skies with snow likely. Cloudy skies with snow.
Temperatures: 16 to 23 deg. F. 11 to 18 deg. F. 17 to 24 deg. F.
Wind direction: S S SE
Wind speed: 15 to 25 mph with gusts to 45 mph. 15 to 25 mph with gusts to 40 mph. 20 to 30 mph with gusts to 45 mph.
Expected snowfall: 2 to 5 in. Up to 2 in. 4 to 8 in.