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.

Snow returned to the forecast area overnight and is expected to continue into Sunday morning. Air temperatures have warmed considerably over the past several days with remote sensors reporting upper twenty's to low thirties in most locations. Snow levels are expected to remain below 5,000' through the weekend due to cold air that remains trapped in the lower valleys. New snow amounts are running 1 to 3 inches this morning across the forecast area. For areas above 7,000', 1 to 2+ feet of new snow are expected over the next 48 hours. Ridgetop winds remain out of the southwest his morning and are forecast to maintain this direction for the next 30 hours. Winds are expected to remain moderate in speed through tonight before increasing on Saturday.

Observations made yesterday on Meiss Ridge on the north side of Carson Pass revealed recent avalanche activity believed to have occurred naturally on Dec 8 or 9 above treeline on a wind loaded NE aspect, 40 degree slope, at 9,000' (click here for photos). Ski cuts placed adjacent to the crown produced no results. Observations made yesterday on the far east ridge of Tamarack Peak near the Mount Rose Hwy Summit revealed a reawakening of instability on the October 19 facet layer. On this below treeline, NW aspect, 31 degree slope at 8,900', this layer had been observed to become stable just prior to the Dec 6-7 snowfall in this exact location. With recent new snow adding load and becoming a cohesive slab above the facet layer, impressive fracture propagation test results were observed yesterday (click here for videos).

Avalanche concern #1:

In near treeline and above treeline areas, wind loading of new snow will accumulate on top slabs formed by non-storm wind loading from the past several days (photo) on NW-N-NE-E aspects. In above treeline areas instability will be limited to the wind transported snow only. In near treeline areas above 8,000' instability may involve the Oct 19 facet layer. The greatest instability concerns at this time exist in near treeline terrain above 8,600' on NW-N-NE aspects that have at least some protection from NE winds where the weak, sugary crystals of the Oct 19 layer sit on top of the early Oct ice mass. Avalanches that fail near the base of the snowpack and involve significant amounts of recent wind loaded snow will have significant destructive potential.

Avalanche concern #2:

Deep slab instability in becoming an increasing concern for below treeline areas on NW-N-NE aspects. With the reawakening of the Oct 19 facet layer, continued new snow loading through the weekend will further stress this existing weak layer. Below treeline avalanches large enough to bury or injure a person will become increasingly likely as this storm cycle progresses. For this weak layer, the greatest concerns exist above 8,600'. Snowpack failure will also be possible just above the thin November 22 rain crust that exists along the Sierra Crest at a variety of elevations. Snowpack failure was observed involving a very thin layer of faceted snow crystals on top of this crust to produce several below treeline avalanches on road cuts in the Pole Creek and Independence Lake areas on Dec 7 during the last storm cycle. A repeat of avalanches involving this layer will again be possible as this storm cycle progresses.

 

 

The bottom line:

Near and above treeline, pockets of CONSIDERABLE danger are expected to form today in wind loaded areas on NW-N-NE-E aspects, 34 degrees and steeper. Below treeline avalanche danger is MODERATE on NW-N-NE aspects, 34 degrees and steeper due to continued instability of a variety of weak layers.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	27 to 30 deg. F.
Max. temperature in the last 24 hours:	28 to 33 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	25 mph
Maximum wind gust in the last 24 hours:	48 mph
New snowfall in the last 24 hours:	1 to 3 inches
Total snow depth:	21 to 35 inches

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

For 7000-8000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Cloudy skies with snow in the morning. A chance of snow in the afternoon.	Cloudy skies with snow.	Cloudy skies with snow.
Temperatures:	26 to 33 deg. F.	21 to 28 deg. F.	23 to 30 deg. F.
Wind direction:	SW	SW	SW shifting to S
Wind speed:	10 to 15 mph with gusts to 35 mph. Winds increasing to 15 to 25 with gusts to 45 mph in the afternoon.	15 to 25 mph with gusts to 45 mph. Gusts decreasing to 35 mph after midnight.	15 to 20 mph with gusts to 35 mph. Increasing to 20 to 30 mph with gusts to 45 mph in the afternoon.
Expected snowfall:	3 to 5 in.	2 to 4 in.	6 to 12 in.
For 8000-9000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Cloudy skies with snow in the morning. A chance of snow in the afternoon.	Cloudy skies with snow.	Cloudy skies with snow.
Temperatures:	27 to 33 deg. F.	20 to 27 deg. F.	21 to 28 deg. F.
Wind direction:	SW	SW	SW shifting to S
Wind speed:	20 to 30 mph with gusts to 50 mph.	20 to 30 mph with gusts to 55 mph.	25 to 40 mph with gusts to 75 mph. Increasing to 50 to 65 mph with gusts to 100 mph in the afternoon.
Expected snowfall:	3 to 6 in.	2 to 4 in.	6 to 12 in.