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 2, 2009:

January 2, 2009 at 7:58 am

Near and above treeline, avalanche danger will rise to MODERATE on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with pockets of MODERATE danger developing in open areas 37 degrees and steeper as the day progresses.

Forecast Discussion:

Precipitation from the weather system currently affecting the forecast area began last night with snow levels 7,500' to 8,000'. Snow levels have fallen to around 6,500' this morning and are expected to fall to below 4,000' as the day progresses. Ridgetop winds are moderate in speed from the southwest this morning, with 100 mph gusts expected to develop over ridges. New snow amounts by late today are forecast to reach 5 to 10 inches of accumulation.

Recent observations from around the forecast area indicate that the snowpack is in good condition to handle the additional load of rain and new snow. Stability tests are still showing some moderate to hard force shears on basal faceted snow layers from November storms and occasionally on mid pack remnants of a needle crystal layer from the mid December storms. Loading these layers to the point of failure has proven difficult and often impossible without removing a portion of the upper snowpack. Any avalanche activity associated with the current weather system is not expected to involve old snow layers.

Today, avalanche danger will rise throughout the day as snow levels lower and new snow accumulates. Air temperatures have started warm and are expected to become progressively colder, placing higher density snow at the bottom and lower density snow at the top of the new snow layer. This will help to keep slab formation limited to wind affected areas. Avalanche activity is expected to remain limited to human triggering in steep wind loaded areas, mainly on NW-N-NE-E-SE aspects through most of the day today. Natural avalanche activity is not impossible, especially very late this afternoon and evening if the upper end of forecast snowfall amounts are reached.


The bottom line:

Near and above treeline, avalanche danger will rise to MODERATE on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is LOW with pockets of MODERATE danger developing in open areas 37 degrees and steeper as the day progresses.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature: 27 deg. F.
Max. temperature in the last 24 hours: 34 deg. F.
Average wind direction during the last 24 hours: West shifting to southwest.
Average wind speed during the last 24 hours: 26 mph
Maximum wind gust in the last 24 hours: 97 mph
New snowfall in the last 24 hours: 1 inches
Total snow depth: 55 to 63 inches

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

For 7000-8000 ft:
  Friday: Friday Night: Saturday:
Weather: Snow, possibly mixed with rain below 7,500 feet before 9am. Snow likely in the evening, then partly cloudy with isolated snow showers. High clouds with periods of sun.
Temperatures: 35 falling to 25 deg. F. 9 to 14 deg. F. 21 to 27 deg. F.
Wind direction: SW SW becoming variable by midnight E
Wind speed: 20 to 35 mph with gusts 50 to 60 mph. 15 to 25 mph with gusts to 40 mph, decreasing to 10 mph or less by midnight Around 10 mph
Expected snowfall: 4 to 8 in. trace to 2 in. O in.

For 8000-9000 ft:
  Friday: Friday Night: Saturday:
Weather: Snow Snow likely in the evening, then partly cloudy with isolated snow showers. High clouds with periods of sun.
Temperatures: 32 falling to 20 deg. F. 7 to 12 deg. F. 16 to 21 deg. F.
Wind direction: SW SW shifting to N NE shifting to E
Wind speed: 35 to 50 mph with gusts 90 to 110 mph. 20 to 35 mph with gusts to 65 mph, decreasing to 10 to 20 mph with gusts to 35 mph. 10 to 20 mph
Expected snowfall: 5 to 10 in. trace to 2 in. O in.