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 is in place over the forecast area and is expected to provide sunny skies and clear nights into Thursday. A chance of snow exists for Thursday night. An air temperature inversion is in place once again this morning with remote sensors reporting the coldest air temperatures in mountain locations below 7,000'. Ridgetop winds remained moderate in speed out of the northeast overnight. Winds are forecast to remain moderate in speed this morning before becoming light this afternoon. Winds are forecast to shift to the southwest on Thursday and increase to moderate in speed.

Persistent weak instability is the correct term for describing the current state of the snowpack in some areas. Locations on NW-N-NE aspects above 8,700' where the October 19 facet layer is sandwiched between the early October ice mass at ground level and recent storm snow at the surface continues to show signs of instability. Observations made Monday in the Mount Rose area pointed to the continued instability of this snowpack structure. On the far east ridge of Tamarack Peak, shooting cracks up to 30 feet and whumpfing were observed below treeline at 8,900' on a NW aspect, 28 degree slope in an area where winds had stiffened the surface tests performed at this location confirmed that stability was poor and that fracture propagation was likely along the Oct 19 facet layer in response to light to moderate forces. In Upper Ophir Creek, similar tests were performed below treeline at 8,800' on a NE aspect, 22 degree slope in a wind protected area. Where the recent storm snow was softer and much less wind affected, fracture propagation was more difficult, but not impossible to create. No shooting cracks or whumpfing were observed in this area, but the current snowpack would not react well to heavy loading. These observations match well with recent observations from the Carson Pass and Independence Lake areas, but bring NW aspects and below treeline areas into the instability picture. In other areas, on other aspects, and/or at lower elevations where the early October ice mass is either absent or not covered by the October 19 facet layer, stability of the existing snowpack is much better. This was observed yesterday at treeline on the NE aspect of Basin Peak (Donner Summit Area) at 8,880' where the ice mass and Oct 19 facet layer were absent and the snowpack structure was stable. A surface rain crust that formed on November 22 was widespread in this area and exists up to 9,000'.

Avalanche concerns for today revolve around the persistent weak instability of the Oct 19 facet layer that continues to allow for the possibility of human triggered avalanches in specific areas. This type of instability is different than the storm snow instability commonly seen in this region. It is expected to remain active within our snowpack for some time to come. Slopes that have continued to show signs of instability are also the slopes that are most attractive for recreation as they hold the (relatively) deepest snowpack. From an avalanche standpoint, these slopes are the most dangerous due to the snowpack layer structure that exists there. Since the overall snowpack is shallow, it is easy to track the presence or absence of the early Oct ice mass by feeling for it with your feet and/or poles. Hand pits have been very effective at looking and feeling for the loose, sugary crystals of the Oct 19 facet layer on top of the ice mass.

The bottom line:

Areas of MODERATE avalanche danger exist above 8,700' on NW-N-NE aspects 32 degrees and steeper both above and below treeline. 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:	30 deg. F.
Max. temperature in the last 24 hours:	42 deg. F.
Average wind direction during the last 24 hours:	Northeast
Average wind speed during the last 24 hours:	33 mph
Maximum wind gust in the last 24 hours:	49 mph
New snowfall in the last 24 hours:	O inches
Total snow depth:	4 to 24 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Sunny skies.	Clear skies.	Sunny skies in the morning, becoming partly cloudy. A chance of snow late.
Temperatures:	42 to 49 deg. F.	28 to 38 deg. F.	43 to 50 deg. F.
Wind direction:	E	Light winds becoming S after midnight.	SW
Wind speed:	Up to 10 mph.	Around 10 mph.	Light winds increasing to 10 to 20 mph with gusts to 30 mph in the afternoon.
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Sunny skies.	Clear skies.	Sunny skies in the morning, becoming partly cloudy. A chance of snow late.
Temperatures:	38 to 45 deg. F.	28 to 35 deg. F.	38 to 45 deg. F.
Wind direction:	E	S	S shifting to SW
Wind speed:	15 to 20 mph with gusts to 35 mph. Winds decreasing to around 10 mph in the afternoon.	10 to 15 mph with gusts to 25 mph.	15 to 25 mph increasing to 20 to 30 mph with gusts to 45 mph in the afternoon.
Expected snowfall:	O in.	O in.	O in.