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.

Lingering cloud cover and snow showers this morning will give way to sunny skies as the day progresses. New snow amounts from the past 24 hours are running 3 to 11 inches across the forecast area. New snowfall amounts are unevenly distributed across the forecast area due to the showery nature of yesterday's snowfall. Ridgetop winds have switched from southwest to northeast overnight and have decreased to light in speed. Light to moderate northeast winds are expected to last through today. Air temperatures this morning are running in the teens across the forecast area. Maximum daytime air temperatures for today are expected to reach the mid teens to low 20s.

Recent Observations:

Observations made yesterday on Jake's Peak (West shore Tahoe area) and on Tamarack Peak (Mount Rose area) revealed ongoing wind slab instability in the upper snowpack. Recently formed wind slabs were very reactive in the observed wind loaded areas both near treeline and below treeline. Skier triggered cracking was observed in wind loaded areas below treeline on Jake's Peak with much better upper snowpack stability observed in wind protected areas (video, more info). An intentionally skier triggered avalanche occurred on Tamarack Peak in wind loaded below treeline terrain at 9,100' on a north aspect 35 degree slope. Crown depth was up to 2' deep. Several other similar wind slab avalanches were noted in the area, having occurred naturally in similar terrain over the previous 12 to 24 hours (photos, more info).

Observations from around the forecast area over the past several days have shown widespread avalanche activity. In some instances, avalanches that initiated on wind slabs in the upper portion of the snowpack have stepped down to failure on deeper facet layers. These facet layers are now buried 3 to 7 feet deep in the snowpack. Where these 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

Recently formed wind slabs sit on top of a weak layer of lower density storm snow.  Lingering instability is expected today in wind loaded areas. The wind shift to NE last night may allow for some additional new wind slab formation today on the traditionally windward SW-W aspects. Widespread distribution of wind slabs exists in wind loaded areas both above and below treeline. Human triggered avalanches involving these slabs remain possible today. The largest and most fragile wind slabs will exist on wind loaded and cross loaded NW-N-NE-E-SE aspects.

Avalanche Problem #2: Persistent Deep Slabs

Faceted snow crystals that exist directly above and below rain crusts that formed in early December are now buried 3 to 7 feet deep in the snowpack. These persistent weak layers are referred to as the Dec 2 and Dec 12 facet layers. In some areas these facet layers have already collapsed under the weight of the overlying snowpack, leading to large avalanches. In other places these layers are still holding on, but are very near a state of failure. 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 NW-N-NE aspects between 7,500 ft. and 10,000 ft. However, they have been noted on some southerly and easterly aspects as well. Due to the depth of these weak layers, they have becoming more difficult to trigger under the weight of a skier or snowmobiler. At this time the most likely trigger is an avalanche that initiates higher in the snowpack and then steps down to these deeper weak layers. Avalanches that result from failure of these facet layers will fracture across wide areas and could easily propagate far above or far to the side of the person who is the trigger. Any avalanches that fail on these facet layers will be large and destructive. Adjust travel tactics accordingly to account for the possibility of triggering large long running avalanches from locations low on slopes and from significant distances away.

The bottom line:

Avalanche danger is MODERATE both above and below treeline on all aspects on slopes 35 degrees and steeper. A mix of recently formed wind slabs and heavy snow loads sitting on top of weak persistent deep slabs will keep large destructive human triggered avalanches possible today. Natural avalanches are unlikely. Adjust travel tactics accordingly to account for the possibility of triggering large long running avalanches from locations low on slopes and from significant distances away.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	10 to 17 deg. F.
Max. temperature in the last 24 hours:	17 to 24 deg. F.
Average wind direction during the last 24 hours:	Southwest shifting to northeast
Average wind speed during the last 24 hours:	18 mph
Maximum wind gust in the last 24 hours:	53 mph
New snowfall in the last 24 hours:	3 to 11 inches
Total snow depth:	69 to 97 inches

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

For 7000-8000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Mostly cloudy skies with isolated snow showers in the morning, becoming partly cloudy.	Clear skies, becoming partly cloudy.	Mostly cloudy skies.
Temperatures:	18 to 23 deg. F.	8 to 14 deg. F.	24 to 29 deg. F.
Wind direction:	NE	Variable	Variable
Wind speed:	10 to 15 mph with gusts to 25 mph.	Light winds.	Light winds.
Expected snowfall:	0 to trace in.	O in.	O in.
For 8000-9000 ft:
	Thursday:	Thursday Night:	Friday:
Weather:	Mostly cloudy skies with isolated snow showers in the morning, becoming partly cloudy.	Clear skies, becoming partly cloudy.	Mostly cloudy skies.
Temperatures:	15 to 20 deg. F.	8 to 14 deg. F.	16 to 23 deg. F.
Wind direction:	N	NE shifting to SE	S
Wind speed:	15 to 25 mph with gusts to 35 mph.	15 to 20 mph with gusts to 30 mph.	10 to 15 mph with gusts to 25 mph in the afternoon.
Expected snowfall:	0 to trace in.	O in.	O in.