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.

High pressure over the forecast area is beginning to shift and open the door for the next storm system expected to affect the forecast area later this weekend. Ahead of the approaching storm system, increasing high clouds and above freezing daytime air temperatures are expected for the next two days in most locations. Ridgetop winds increased in speed out of the southwest last night, but are expected to decrease and become light as the day progresses.

Deep slab instability continues to linger within the forecast area. Very large human triggers are required to cause an avalanche. Evidence indicates that a single skier, snowboarder, or snowmobiler is unlikely to trigger an avalanche. A trigger such as a very large section of cornice with it's mass measured in tons is required.

Yesterday, observations made on Ralston Peak (Desolation Wilderness area), on Jake's and Rubicon Peaks (West Shore Tahoe area), and on Mt. Judah (Donner Summit area) all indicated the presence of a stable snowpack. Stability tests indicated continued strengthening of the recent storm snow. Tests also indicate strengthening of the January 22-23 rain crust / faceted snow interface below the recent storm snow, but at a slower rate. Human triggering of this weak layer is becoming increasingly more difficult, but fracture propagation is still possible. On Mt. Judah, very large cornice sections measuring up to 10' by 60' and likely weighing several tons (train car sized) were dropped onto the slope below with no avalanche activity resulting from the trigger. Widespread ski and snowmobile tracks have been observed throughout the forecast area on steep terrain at all elevations with minimal to no evidence of instability observed.

A group of skiers found deep slab instability yesterday on Castle Peak (Donner Summit area) on the ridge to the east of the summit at approximately 8,700' on a N aspect, steeper than 35 degrees. The group selected a very large cornice, cut the cornice (photo) and had it collapse larger than anticipated (photo) dropping a section of cornice measuring 10' by 25', likely weighing in excess of 6,000 lbs onto the slope below. This caused an avalanche in the gully directly below the cornice with sympathetic release of  two avalanches in adjacent gullies (photo 1, photo 2). Fracture propagation created an additional crown mid slope (photo). The exact failure layer within the snowpack is unknown, but based on the crown height from the photos and the amount of fracture propagation, the January 22-23 rain crust / facet layer is suspected. Attempts to confirm this will be made today. During the next hour following this avalanche occurrence, snowmobiles were reported to repeatedly high mark immediately adjacent slopes with no further instability.

Increasing winds overnight may have cause very small pockets of wind loading in lee areas near and above treeline on NE aspects. These slabs are expected to be very small and not present a significant threat to backcountry travelers today. Several reports of tender cornices have been received over the past few days, with intentional and unintentional human triggered collapse of large cornice sections. Large human triggered avalanches due to deep slab instability remain unlikely but not impossible. Triggering a large avalanche will remain very difficult today with a very large trigger required. Any large human triggered avalanche activity today is expected to remain very isolated. In the unlikely event of a human triggered avalanche, the size of the avalanche may be quited large with a crown of 3 to 7 feet and severe consequences possible.

The bottom line:

Avalanche danger is LOW for all elevations and aspects. Human triggered avalanches are unlikely but not impossible today. An unlikely human triggered avalanche may be large with severe consequences possible. Use normal caution and good travel habits while in the backcountry.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	23 deg. F.
Max. temperature in the last 24 hours:	33 to 35 deg. F.
Average wind direction during the last 24 hours:	South shifting to southwest.
Average wind speed during the last 24 hours:	25 mph
Maximum wind gust in the last 24 hours:	42 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	113 inches

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

For 7000-8000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Sunny skies with increasing high clouds.	Partly cloudy skies.	Partly cloudy skies in the morning, becoming mostly cloudy.
Temperatures:	37 to 44 deg. F.	25 to 30 deg. F.	39 to 46 deg. F.
Wind direction:	W shifting to SW	S	S
Wind speed:	Light winds.	Light winds.	Increasing to 10 to 20 mph.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Sunny skies with increasing high clouds.	Partly cloudy skies.	Partly cloudy skies in the morning, becoming mostly cloudy.
Temperatures:	32 to 37 deg. F.	23 to 28 deg. F.	34 to 39 deg. F.
Wind direction:	W shifting to SW	S to SW	SW
Wind speed:	15 to 25 mph, decreasing to 10 to 15 mph by afternoon.	Up to 10 mph in the evening, increasing to 10 to 20 mph overnight.	10 to 20 mph with gusts to 30 mph, increasing to 15 to 25 mph with gusts to 40 mph in the afternoon.
Expected snowfall:	O in.	O in.	O in.