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.

A splitting weather system will move through the forecast area today. Winds ahead of the system have mixed out most of the strong air temperature inversion that has existed over the forecast area for the past week. Remote sensors are reporting air temperatures in the upper teens to mid 20s across the elevation spectrum of the forecast area this morning. Ridgetop winds shifted from southwest to northeast last night and will remain out of the northeast through tomorrow. Wind speeds will gradually increase today into tomorrow, becoming moderate to strong in speed. New snowfall amounts of 3 to 6 inches are forecast for today with the greatest accumulation expected along the Sierra Crest south of Hwy 50.

Recent Observations:

Two small avalanches were individually triggered around 1:30 pm yesterday by a snowboarder and a skier in the Frog Lake Cliffs area on the south side of Carson Pass. These avalanches failed on a 3 to 4 inch thick wind slab that had formed in open near treeline terrain. The slope was reported as a NE aspect at 8,900' with a slope angle in excess of 40 degrees. The first triggered avalanche propagated around 150 feet wide. The second triggered avalanche propagated into the first avalanche (photos, more info). The amount of snow involved was deemed insufficient to create a full burial. The same party encountered no snowpack instability while ascending/descending Round Top Peak earlier that day.

Observations made yesterday on Donner Peak (Donner Summit area), off Hwy 267 Brockway Summit, and in Horse Canyon (Bear Valley area) revealed surface hoar persisting on northerly aspects and other well shaded areas. Crystal sized ranged to 3mm to 2.5cm and was prevalent in open areas below treeline. The largest crystals were observed at lower elevations that had experienced colder nighttime air temperatures under inversion conditions (photos, more info). Snowpit tests targeting the Dec 2 and Dec 12 facet layers showed continued improving stability (video, pit profile, more info). In Horse Canyon, a reactive layer of buried surface hoar was observed 6 inches below the snow surface at the snowpit location on a N aspect at 8,000' (pit profile, more info).

Avalanche Problem #1: Wind Slabs

Shallow wind slabs will be found today on a variety of aspects near and above treeline. New snow and wind will build fresh wind slabs in lee areas as the day progresses. By this afternoon, wind slabs greater than 1 foot thick will be possible in the areas that receive higher end snowfall amounts in addition to significant direct wind loading and/or cross loading.

Avalanche Problem #2: Storm Slabs

New snow is expected to bury surface hoar in a variety of below treeline areas today. As new snow depth increases, unstable snow is expected to form in open areas on NW-N-NE aspects and other heavily shaded areas. Lower angle slopes down to around 30 degrees may experience soft slab avalanches in response to human triggers. Steeper slopes may experience soft slab or loose dry snow avalanches in response to human triggers. While the slab depth should be limited to 6 inches or less, terrain traps such as creek beds could easily create full burial from small avalanches. Expect wide propagation in areas where buried surface hoar exists.

The bottom line:

Near and above treeline, MODERATE avalanche danger will spread to all aspects on slopes 35 degrees and steeper due to unstable wind slabs. Below treeline, areas of MODERATE avalanche danger will form today on NW-N-NE aspects on slopes 30 degrees and steeper due to storm slabs deposited on top of surface hoar.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	19 to 25 deg. F.
Max. temperature in the last 24 hours:	31 to 38 deg. F.
Average wind direction during the last 24 hours:	Southwest shifting to northeast
Average wind speed during the last 24 hours:	25 mph
Maximum wind gust in the last 24 hours:	40 mph
New snowfall in the last 24 hours:	0 to trace inches
Total snow depth:	59 to 86 inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Cloudy skies with snow in the morning. A chance of snow in the afternoon.	Mostly cloudy skies.	Mostly cloudy skies.
Temperatures:	19 to 26 deg. F.	15 to 22 deg. F.	27 to 34 deg. F.
Wind direction:	NE	NE	NE
Wind speed:	10 to 20 mph with gusts to 30 mph.	15 to 20 mph with gusts to 30 mph.	20 to 30 mph with gusts to 40 mph.
Expected snowfall:	3 to 5 in.	O in.	O in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Cloudy skies with snow in the morning. Snow likely in the afternoon.	Mostly cloudy skies.	Mostly cloudy skies.
Temperatures:	16 to 23 deg. F.	14 to 21 deg. F.	24 to 31 deg. F.
Wind direction:	NE	NE	NE
Wind speed:	15 to 25 mph with gusts to 35 mph.	25 to 35 mph with gusts to 45 mph.	25 to 35 mph with gusts to 50 mph, increasing to 35 to 45 mph with gusts to 60 mph in the afternoon.
Expected snowfall:	3 to 6 in.	O in.	O in.