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 15, 2012:


January 15, 2012 at 7:57 am

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


Forecast Discussion:


A storm system passing to the north of the forecast area today and tomorrow will move a dry cold front through the region. Ridgetop winds are steadily increasing this morning. Gale force southwest winds with ridgetop gusts over 100 mph will occur today and continue through this evening. Maximum daytime air temperatures today will reach into the 20s and 30s for areas above 7,000'. For all but the far southern portion of the forecast area, some light snow showers may occur with frontal passage late today and tonight with no accumulation expected. After cold front passage occurs, clearing skies will allow for single digit air temperatures overnight. Sunny skies with moderate winds and maximum air temperatures above 7,000' in the teens and 20s are expected for tomorrow.

Observations:

For the snowpack that exists at this time, surface crust overlying varying amounts of faceted snow is the general theme. Areas along the Sierra Crest in the northern half to third of the forecast area hold the most snow. Elsewhere, significantly less snow exists. The warming and rain event that occurred on December 28-29 added either a rain crust or melt freeze crust to the snow surface in nearly all areas on NW-N-NE-E aspects. Since that time, faceting has continued below this crust and in other layers of the snowpack. Sufficient time has passed to allow for significant weakening of the faceted snow directly below the surface crust. Areas where the snowpack remains in a strong melt-freeze state from top to bottom still exist, but are becoming increasingly isolated. This is mainly seen in areas of hold over snow from last winter and in a few spots that have not undergone significant faceting since the Dec 28-29 event. SE-S-SW-W aspects are generally void of snow except for a few shallow patches in heavily shaded areas.

Avalanche Concerns:

Despite the increasing presence of weak faceted snow in many areas, avalanche activity remains unlikely at this time. In the areas with the deepest snowpack, very strong and supportable surface crusts are keeping the faceted snow below from collapsing when loaded. In areas where the crust is breakable, it is too brittle to sustain propagation. In areas where less snow exists, significant anchors are holding the snowpack in place. The right combination of slab, weak layer, and bed surface necessary for avalanche activity has not been observed within the forecast area at this time.


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: 25 to 30 deg. F.
Max. temperature in the last 24 hours: 39 to 45 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 29 mph
Maximum wind gust in the last 24 hours: 51 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 0 to 18 inches

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

For 7000-8000 ft:

  Sunday: Sunday Night: Monday:
Weather: Partly cloudy skies. Mostly cloudy skies with a slight chance of snow showers in the evening. A chance of snow showers after midnight. Partly cloudy skies.
Temperatures: 30 to 37 deg. F. 6 to 13 deg. F. 17 to 24 deg. F.
Wind direction: SW SW shifting to W after midnight. NW
Wind speed: 30 to 40 mph with gusts to 65 mph. 30 to 40 mph with gusts to 60 mph, shifting and decreasing to 20 to 30 mph with gusts to 40 mph after midnight. 10 to 15 mph with gusts to 30 mph in the morning, decreasing to around 10 mph in the afternoon.
Expected snowfall: O in. 0 to trace in. O in.

For 8000-9000 ft:

  Sunday: Sunday Night: Monday:
Weather: Partly cloudy skies. Mostly cloudy skies with a slight chance of snow showers in the evening. A chance of snow showers after midnight. Partly cloudy skies.
Temperatures: 26 to 33 deg. F. 3 to 10 deg. F. 16 to 22 deg. F.
Wind direction: SW SW W shifting to SW in the afternoon.
Wind speed: 60 to 80 mph with gusts to 100 mph. 60 to 80 mph with gusts to 105 mph, decreasing to 45 to 60 mph with gusts to 75 mph after midnight. 20 to 25 mph with gusts to 35 mph, shifting and decreasing to 10 to 15 mph with gusts to 25 mph in the afternoon.
Expected snowfall: O in. 0 to trace in. O in.