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 3, 2012:


January 3, 2012 at 7:40 am

LOW avalanche danger exists for all elevations and aspects. Normal caution is advised.


Forecast Discussion:


A weak weather disturbance passing through Nevada early this morning is creating moderate speed ridgetop winds. This has prevented any significant air temperature inversion from forming overnight. Remote sensors are reporting air temperatures in the 30s this morning for locations above 7,000'. Ridgetop winds are forecast to remain out of the southwest today, becoming light this afternoon. Maximum daytime air temperatures are expected in the 40s today for areas above 7,000'. Continued light winds and a few additional degrees of warming are forecast for Wednesday. Warm and dry weather punctuated by a few windy periods is expected to continued for the next seven days.

Observations:

Recent observations from around the forecast area, including those made yesterday on Mt. Tallac (Desolation Wilderness area) reveal a stabilizing trend in the existing snowpack. The warming and rain event that occurred on December 28-29 added free water to the snowpack. This free water allowed for significant rounding and bonding of faceted snow that had existed for most of the season in the middle and lower portions of the snowpack. As the snowpack has refrozen over the past few days, the entire snowpack has gained strength. This significant structural change and increase in strength has been noted along the Sierra Crest up to at least 9,000'. Most areas above 9,000' have been significantly wind scoured. Snow surface conditions in most areas range from breakable to supportable crust anywhere from 1/2 inch to 6 inches thick.

Avalanche Concerns:

Avalanche concerns at this time are few. The Dec 28-29 warming event created significant changes in the existing snowpack, especially north of Hwy 80 in what were the most worrisome areas. Now that the persistent weak layer of basal facets has been mostly destroyed, a strong and stable snowpack exists in most snow covered areas. Despite warm daytime air temperatures, wet snow instability is not expected to form on NW-N-NE-E aspects due to weak solar radiation at this time of year. SE-S-SW-W aspects are generally void of snow, negating concerns for wet snow instability on the aspects that receive the higher amounts of solar radiation.


The bottom line:

LOW avalanche danger exists for all elevations and aspects. Normal caution is advised.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 33 to 39 deg. F.
Max. temperature in the last 24 hours: 41 to 48 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 39 mph
Maximum wind gust in the last 24 hours: 57 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 2 to 18 inches

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

For 7000-8000 ft:

  Tuesday: Tuesday Night: Wednesday:
Weather: Partly cloudy skies. Partly cloudy skies. Partly cloudy skies.
Temperatures: 43 to 50 deg. F. 28 to 36 deg. F. 46 to 53 deg. F.
Wind direction: SW SW SW
Wind speed: 10 to 15 mph with gusts to 35 mph. Winds decreasing to up to 10 mph in the afternoon. Light winds Around 10 mph.
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Tuesday: Tuesday Night: Wednesday:
Weather: Partly cloudy skies. Partly cloudy skies. Partly cloudy skies.
Temperatures: 43 to 49 deg. F. 32 to 38 deg. F. 44 to 51 deg. F.
Wind direction: SW SW shifting to S SW
Wind speed: 20 to 30 mph with gusts to 60 mph. Winds decreasing to 10 to 15 mph with gusts to 30 mph in the afternoon. Around 10 mph. 10 to 15 mph.
Expected snowfall: O in. O in. O in.