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.

Snowfall intensity rates are winding down this morning. Snowfall is forecast to decrease to shower activity, but continue through most of this afternoon. An additional 4 to 7 inches of new snow are expected today, most of it accumulating early this morning. New snow amounts from the past 24 hours are running 8 to 16 inches. The greatest new snow amounts have been observed along the Sierra Crest from Hwy 50 northward. Ridgetop winds are moderate to strong in speed this morning out of the southwest. Winds are expected to decrease to moderate in speed this afternoon. Air temperatures this morning are in the mid teens to mid 20s across the forecast area. Only a few degrees of daytime warming are forecast to occur today. Air temperatures for tomorrow will be similar to today, but with light winds.

Recent Observations:

Observations from around the forecast area over the past several days have shown continued snowpack instability. The upper snowpack contains wind slabs and lower density storm snow weak layers. The middle snowpack contains near crust faceted snow crystals that make up the Dec 2 and Dec 12 persistent weak layers. Avalanche activity has occurred in both the upper and middle portions of the snowpack in recent days. In some instances, avalanches that initiated on wind slabs in the upper portion of the snowpack have stepped down to failure on the deeper facet layers. These facet layers are now 4 to 7 feet deep in the snowpack. Where the facet layers have failed, propagation has been rather far, creating hard slab avalanches up to 1/8 mile wide (pit profiles, photos, videos, more info).

Avalanche Problem #1: Wind Slabs and Storm Slabs

New snow and wind created another round of wind slab and storm slab formation over the past 24 hours. Widespread distribution of these slabs is expected today both above and below treeline. Below these slabs are a variety of weak layers ranging from storm snow weaknesses to density changes to deeply buried persistent weak layers. Widespread human triggered avalanches involving these slabs are likely today. The largest and most fragile wind slabs will exist on wind loaded and cross loaded NW-N-NE-E-SE aspects in both above and below treeline terrain. In wind protected areas, softer and smaller storm slabs may exist.

Avalanche Problem #2: Persistent Deep Slabs

Faceted snow crystals that exist directly above and below rain crusts that formed in early December (the Dec 12 and the Dec 2 facet layers mentioned above) are now buried 4 to 7 feet deep in the snowpack. In some areas these facet layers have already collapsed under the weight of the overlying snowpack, leading to large avalanches. In other places they are still holding on. Variability in the strength and distribution of these layers means uncertainty remains as to exactly where and when these facet layers will continue to fail. The most well developed and weakest facets exist on the NW-N-NE aspects between 7,500 ft. and 10,000 ft. However, they have also been noted on some southerly and easterly aspects. All of these areas have received additional new snow loading over the past 24 hours. This will continue to stress these already weak snowpack layers. Avalanches that result from failure of these layers will fracture across wide areas and could easily propagate far above or far to the side of the person who is the trigger. Other avalanches that initiate higher in the snowpack may step down to these deeper weak layers. Any avalanches that fail on these facet layers will be large and destructive. Adjust travel tactics accordingly to account for the possibility of triggering long running avalanches from low on slopes and from significant distances away.

The bottom line:

Avalanche danger is CONSIDERABLE both above and below treeline on NW-N-NE-E-SE aspects on slopes 32 degrees and steeper. For all other areas, avalanche danger is MODERATE. A mix of newly formed wind slabs and heavy snow loads sitting on top of already weak persistent deep slabs will keep large destructive human triggered avalanches likely today. Natural avalanches are possible. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	17 to 22 deg. F.
Max. temperature in the last 24 hours:	23 to 28 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:	66 mph
New snowfall in the last 24 hours:	8 to 16 inches
Total snow depth:	65 to 97 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy skies with snow showers.	Cloudy skies with scattered snow showers.	Mostly cloudy skies with isolated snow showers possible.
Temperatures:	19 to 24 deg. F.	12 to 18 deg. F.	18 to 23 deg. F.
Wind direction:	SW	SW shifting to W	Variable
Wind speed:	30 to 35 mph with gusts to 50 mph, decreasing to 20 to 25 mph with gusts to 35 mph in the afternoon.	10 to 20 mph with gusts to 30 mph in the evening, decreasing to 5 to 15 mph.	Light winds.
Expected snowfall:	4 to 7 in.	Up to 2 in.	0 to trace in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Cloudy skies with snow showers.	Cloudy skies with scattered snow showers.	Mostly cloudy skies with isolated snow showers possible.
Temperatures:	15 to 20 deg. F.	10 to 16 deg. F.	15 to 21 deg. F.
Wind direction:	SW shifting to W	W	NW shifting to NE in the morning.
Wind speed:	45 to 50 mph with gusts to 80 mph, decreasing to 30 to 35 mph with gusts to 55 mph in the afternoon.	25 to 30 mph with gusts to 50 mph, decreasing to 10 to 20 mph with gusts to 30 mph after midnight.	10 to 20 mph with gusts to 35 mph.
Expected snowfall:	4 to 7 in.	Up to 2 in.	0 to trace in.