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 major change in the weather pattern is in store beginning this afternoon as a weather system passes to the east of the forecast area. A transition from warm and sunny to cold and windy takes effect today. Maximum daytime highs in the 30s to 40s this morning will fall to the teens to 20s this afternoon. Ridgetop winds are forecast to shift from west to northeast this afternoon and become gale force in speed with gusts over 100 mph expected tonight and tomorrow. Increasing cloud cover through the day today will bring isolated snow showers to the region tonight and tomorrow morning with no significant accumulation expected.

Observations:

Observations made yesterday on Relay Peak (Mount Rose area) continued to show instability on the November 18 facet layer similar to other locations around the forecast area (pit profile, photos, more info). The most significant change now occurring is that in some areas, the overlying slab composed of snow from the Nov 18-19 storm events has now faceted and weakened to the point that it will no longer sustain propagation. While the Nov 18 layer below it still cracks and fails, so does the overlying slab, keeping slab avalanche activity from occurring. Skier triggered whumpfing and shooting cracks still occur in areas where the November 18 facet layer remains highly developed. In areas where the facets are less developed, snowpit tests continue to show that once fracture is initiated along this weak layer, propagation remains possible if the overlying slab is strong. Areas where significant anchoring exist have shown better stability, but the snowpack in these areas is generally too shallow for over snow recreation. Some lingering instability of shallow wind slabs that formed last week have been observed in isolated areas of previous wind loading near and above treeline. A thin and breakable rain crust that formed on Thanksgiving Day exists on the snow surface along the Sierra Crest up to around 9,000' in most areas.

Avalanche Concern #1: Persistent slabs

Due to the changes in the strength of the overlying slab, locations where all of the ingredients for a slab avalanche to occur are now existing more in pockets.The November 18 facet layer has shown some gains in strength, but they are slow. This is a persistent weak layer and it will take at least several more weeks for this layer to stabilize in all areas. Once new snow returns to the forecast area in significant amounts, this weak layer is likely to become more active rather than sit in a stable state. In locations where the snowpack is deepest, a one to two foot thick slab exists on top of the facet layer. The greatest areas of instability have been observed on N-NE aspects above 8,000', with less frequent areas of instability on NW and E aspects. Heavily shaded, colder slopes with a relatively deeper snowpack and few visible anchors protruding through the snow surface are the most suspect.

Avalanche Concern #2: Wind slabs

The upcoming strong wind event will scour many of the slabs in areas that are not capped by a rain crust. Until that occurs, isolated pockets of lingering wind slab remain in previously wind loaded areas near and above treeline on NW-N-NE-E aspects. These wind slabs are generally less than one foot thick and difficult to trigger.

The bottom line:

Above 8,000', pockets of MODERATE avalanche danger exist both above and below treeline on NW-N-NE-E aspects on slopes 35 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:	29 to 32 deg. F.
Max. temperature in the last 24 hours:	46 to 49 deg. F.
Average wind direction during the last 24 hours:	West
Average wind speed during the last 24 hours:	20 mph
Maximum wind gust in the last 24 hours:	35 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	7 to 23 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Sunny skies in the morning, then becoming partly cloudy.	Partly cloudy in the evening, then clearing. Isolated snow showers.	Sunny skies. Isolated snow showers in the morning.
Temperatures:	40 to 45 degrees falling in the afternoon to 25 to 30 deg. F.	11 to 18 deg. F.	18 to 25 deg. F.
Wind direction:	W shifting to NE	NE	NE
Wind speed:	10 to 20 mph with gusts to 40 mph, increasing to 15 to 25 mph with gusts to 50 mph in the afternoon.	25 to 35 mph increasing to 30 to 45 mph after midnight. Gusts to 65 mph.	30 to 45 mph with gusts to 65 mph.
Expected snowfall:	O in.	0 to trace in.	0 to trace in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Sunny skies in the morning, then becoming partly cloudy.	Partly cloudy in the evening, then clearing. Isolated snow showers.	Sunny skies. Isolated snow showers in the morning.
Temperatures:	35 to 45 falling to 17 to 25 deg. F.	9 to 16 deg. F.	13 to 20 deg. F.
Wind direction:	W shifting to NE	NE	NE
Wind speed:	25 to 35 mph with gusts to 70 mph.	40 to 60 mph increasing to 50 to 70 mph after midnight. Gusts to 105 mph.	50 to 70 mph with gusts 100 to 110 mph.
Expected snowfall:	O in.	0 to trace in.	0 to trace in.