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 continues to dominate the weather pattern over the forecast area for at least today and tomorrow. Ridgetop winds out of the west to southwest began increasing in speed yesterday and are forecast to further increase in speed today. Remote sensors are reporting air temperatures this morning at the 8,000' level in the upper 20s. Continued warming is expected today with maximum daytime air temperatures above 7,000' ranging from the low 30s to low 40s. The next opportunity for some amount of precipitation over the forecast area appears to occur on Thursday, with low confidence in the details at this time.

Observations:

Observations made yesterday in the Carson Pass area revealed continued instability of recent new snow on top of the November 18 facet layer. An overall shallow snowpack in this area allowed for the influence of anchoring by rocks and logs in areas where the snowpack was less than two feet deep to keep evidence of instability to a minimum. Conversely, unanchored pockets of steeper shaded terrain on N-NE aspects where the snowpack was 2 to 2.5 feet deep responded to the weight of a skier with whumpfing (collapse) and shooting cracks. Snowpit tests in these areas gave further indications of likely propagation along the top of the Nov 18 facet layer (pit profile, photo, more info). This has been the trend of the past few days. Areas that hold the deepest snowpack also hold the greatest instability. Increasing ridgetop winds were observed to further enhance existing wind slab development on NW-N-NE-E aspects yesterday. Snowpit tests in wind loaded areas also revealed likely propagation of slab failure along the interface of the surface wind slab and the recent new snow below.

Avalanche Concern #1: Persistent slabs

Persistent weak instability common in early season shallow snowpacks exists throughout the forecast area. The Nov 18 facet layer ranges from lightly faceted to very faceted and from 2 to 10 inches deep across NW-N-NE-E aspects above 8,000'. Equal instability has been observed both above and below treeline as this is a persistent weak layer problem rather than a storm snow and wind loading problem. N-NE aspects have shown the greatest instability. Zones within the forecast area than have been most favored by November snowfall have also show the greatest amount of instability on this weak layer. Generally the area along the Sierra Crest from Blackwood Canyon north through Donner Summit and the Independence Lake holds the most snow available for recreation and also has the most snowpack instability. Ongoing whumpfing, shooting cracks, and unstable snowpit test results from the last 3 days continue to show unstable conditions with little to no evidence of stabilization. Human triggered avalanches are possible to likely on most steep slopes that hold sufficient snow cover for winter recreation endeavors.

Avalanche Concern #2: Wind slabs

Ongoing wind transport of snow on the ground is further enhancing the depth and width of existing wind slabs. Most instability associated with wind slab formation yesterday was noted at the interface of the wind slab and recent new snow below. However, in some areas these slabs are forming on top of and adding further load to the Nov 18 facet layer. As increasing amounts of wind transported snow are added to the snowpack, an isolated natural avalanche in not out of the question, especially on N-NE aspects near and above treeline. The amount of snow still available on SW-W aspects for wind transport is diminishing, so obvious blowing snow along the ridgetops may become less obvious as the day progresses. Expect the possibility of human triggered avalanches today in wind loaded areas near and above treeline on NW-N-NE-E aspects.

The bottom line:

On NW-N-NE-E aspects, avalanche danger is MODERATE both above and below treeline for areas above 8,000 ft on slopes 32 degrees and steeper. Along the Sierra Crest in the northern half of the forecast area, pockets of CONSIDERABLE danger exist on N-NE aspects both above and below treeline in areas above 8,000 ft on slopes 32 degrees and steeper. For all other areas, avalanche danger is LOW.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	26 to 29 deg. F.
Max. temperature in the last 24 hours:	25 to 30 deg. F.
Average wind direction during the last 24 hours:	West shifting to southwest
Average wind speed during the last 24 hours:	43 mph
Maximum wind gust in the last 24 hours:	73 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	12 to 30 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Partly cloudy skies.	Partly cloudy skies.	Partly cloudy skies.
Temperatures:	36 to 40 deg. F.	22 to 32 deg. F.	36 to 43 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	20 to 30 mph with gusts to 60 mph	20 to 30 mph with gusts to 60 mph. Gusts decreasing to 50 mph after midnight.	15 to 25 mph with gusts to 55 mph.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Partly cloudy skies.	Partly cloudy skies.	Partly cloudy skies.
Temperatures:	33 to 38 deg. F.	23 to 29 deg. F.	33 to 38 deg. F.
Wind direction:	SW	SW	SW
Wind speed:	25 to 45 mph with gusts to 60 mph. Gusts increasing to 80 mph in the afternoon.	30 to 45 with gusts to 70 mph.	30 to 50 mph with gusts to 80 mph
Expected snowfall:	O in.	O in.	O in.