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.

This morning a slight in version has formed with temperatures in the lower elevations in the low 30's while remote sensors above 8000 ft. indicate temps have already climbed into the upper 30's to low 40's. The forecast calls for another spring-like day due to the high pressure ridge over the forecast area. Daytime highs above 7000 ft. should reach the upper 40's to mid 50's. The winds should remain light and skies should remain mostly clear. This pattern of warm sunny weather should continue through the weekend.

Observations:

Yesterday on Mt. Judah (Donner Pass area), observations showed a shallow snowpack with several anchors (trees, rocks, stumps logs, etc) at most elevations. On the most wind-loaded slopes, up to 2.5 ft of snow existed near the ridgelines. Small localized wind slabs still remained on these slopes. As one moved downhill from the ridgelines, the snowpack quickly shrank to under 1.5 ft. in depth. The Nov, 18th facets do exist in this area above 8000 ft. on the N-NE-E aspects, and snowpit data did indicate that fractures can occur in this layer even though they are harder to trigger. However, observations also showed that this persistent weak layer is less continuous and much thinner in this area. No human-triggered cracking, whumpfing, or collapsing occurred on either the Nov. 18th facets or the small wind slabs near ridgelines in this area. Observations revealed a breakable rain crust on the snow surface on all aspects up to 8200 ft. in the Mt. Judah area yesterday as well. A melt-freeze crust had also started to form on the more sun-exposed aspects.

Avalanche Concern #1: Persistent slabs

A persistent weak layer like the Nov. 18th facets usually does not stabilize very fast. Often layers like this need to be physically removed by melting or by avalanche activity. If not, they can take several weeks to months to gain strength. The warm sunny weather in the next few days will help slow the faceting process down; however, it should not be enough to reverse the faceting that has already occurred on the the northerly slopes above 8000 ft. The ingredients for avalanche activity will remain with the Nov 18 facet layer as a persistent weak layer and the recent snow on top of it as a slab layer. This combination will allow the possibility of human-triggered avalanche activity to continue today in both above and below treeline terrain. In areas where the snowpack has this structure with a very shallow snowpack, anchors poking through the snowpack help prevent fractures in the weak layer from traveling very far. Of course, these same anchors also tend to damage skis, boards, snowmobiles, and people. The areas that hold a deeper snowpack and better recreation potential also hold the weakest snowpack. The N-NE aspects above 8000 ft. that had the most snow in Oct. and early Nov. represent these deeper and weaker slopes where the thickest and weakest facets exist under the largest slabs.

The bottom line:

For areas above 8,000 ft. both above and below treeline, MODERATE avalanche danger exists on slopes 32 degrees and steeper on N-NE aspects. Pockets of MODERATE danger remain in the these areas on the NW and E aspects as well. The avalanche danger is LOW in all other areas.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	38-42 deg. F.
Max. temperature in the last 24 hours:	40-45 deg. F.
Average wind direction during the last 24 hours:	Northwest shifting to the northeast
Average wind speed during the last 24 hours:	15 mph
Maximum wind gust in the last 24 hours:	49 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	9-25 inches

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

For 7000-8000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Mostly sunny with a few high thin clouds	Partly cloudy	Mostly sunny with a few high thin clouds
Temperatures:	47-54 deg. F.	30-38 deg. F.	54-60 deg. F.
Wind direction:	Variable shifting to the south in the afternoon	Variable becoming southwest after midnight	Southwest
Wind speed:	Light	up to 10 mph with gusts to 25 mph after midnight	10-15 mph with gusts to 25 mph increasing to gusts to 35 mph in the afternoon
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Mostly sunny with a few high thin clouds	Partly cloudy	Mostly sunny with a few high thin clouds
Temperatures:	45-52 deg. F.	32-39 deg. F.	50-56 deg. F.
Wind direction:	Variable shifting to the south in the afternoon	Southwest	Southwest
Wind speed:	10-15 mph with gusts to 30 mph in the afternoon	10-20 mph with gusts to 35 mph	15-25 mph with gusts to 40 mph
Expected snowfall:	O in.	O in.	O in.