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 16, 2012:


January 16, 2012 at 7:46 am

Avalanche danger remains LOW for all elevations and aspects. Normal caution is advised.


Forecast Discussion:


The cold front that passed through the region over the last 24 hours ushered in a cold and dry air mass. A trace to half inch of now snow fell over the northern portion of the forecast area last night. Air temperatures are in the single digits and teens this morning throughout the forecast area. Yesterday's gale force ridgetop winds have become light this morning. Sunny skies, light to moderate speed winds, and maximum daytime air temperatures in the teens to mid 20s are expected today for areas above 7,000'. Limited daytime warming will set up for another cold night tonight. On Tuesday, increasing southwest ridgetop winds and some increase in cloud cover are forecast to occur ahead of the well advertised storm system expected to impact the area on Wednesday.

Observations:

New snowfall amounts last night of 0 to 0.5 inches did little to change the current snowpack. The general theme remains surface crust overlying varying amounts of faceted snow. Areas along the Sierra Crest in the northern half to third of the forecast area hold the deepest snowpack. 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 within 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 will remain unlikely for a couple more days. 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 slab avalanche activity has not been observed within the forecast area at this time. Increased avalanche danger is expected to occur later this week as storm systems bring a new load to the snowpack..


The bottom line:

Avalanche danger remains LOW 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: 4 to 14 deg. F.
Max. temperature in the last 24 hours: 26 to 33 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 78 mph
New snowfall in the last 24 hours: 0 to 0.5 inches
Total snow depth: 0 to 18 inches

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

For 7000-8000 ft:

  Monday: Monday Night: Tuesday:
Weather: Mostly cloudy skies in the morning, becoming partly cloudy. Partly cloudy skies. Partly cloudy skies in the morning, becoming mostly cloudy.
Temperatures: 17 to 24 deg. F. 3 to 10 deg. F. 25 to 32 deg. F.
Wind direction: W SW SW
Wind speed: Up to 10 mph. 10 to 15 mph. 10 to 20 mph with gusts to 30 mph.
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Monday: Monday Night: Tuesday:
Weather: Mostly cloudy skies in the morning, becoming partly cloudy. Partly cloudy skies. Partly cloudy skies in the morning, becoming mostly cloudy.
Temperatures: 16 to 22 deg. F. 3 to 10 deg. F. 26 to 32 deg. F.
Wind direction: W SW SW
Wind speed: 10 to 15 mph with gusts to 25 mph in the afternoon. 10 to 20 mph with gusts to 30 mph, increasing to 20 to 25 mph with gusts to 40 mph after midnight. 25 to 40 mph with gusts to 60 mph.
Expected snowfall: O in. O in. O in.