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.

Continued snow showers through much of yesterday deposited another 2 to 8 inches of snow across the forecast area. This brings the three day storm total at 8,200' up to 13 to 26 inches of accumulated snowfall. For today, cloudy skies, increasing winds, and snow showers will be the major weather as another storm system moves into the forecast area. Maximum daytime temperatures in the low 20s to low 30s are expected. Ridgetop winds will remain out of the southwest, increasing from moderate to strong in speed. Snow shower activity is forecast to increase as the day progresses with up to 2 inches of accumulation by this evening. Once the brunt of the approaching storm arrives tonight, an additional 18 to 32 inches of snowfall is expected above 7,000' tonight and tomorrow with snow level around 5,000'. The period of highest intensity snowfall is expected between 1am and 10am Monday.

Observations:

Field data collected yesterday on Castle Peak (Donner Summit area) revealed that significant amounts of rain had fallen up to at least 8,700' prior to the lowering of snow levels early yesterday morning. This rain had melted the rain crust that formed on December 28-29 and destroyed the faceted crystals that had existed above and below the crust. A new much thicker rain crust now exists at the base of the recent storm snow and is in the process of refreezing. Within the storm snow, a density inversion of higher density snow on top of lower density new snow was noted to have contributed to storm slabs in wind protected areas and wind slabs in wind exposed areas. Minor skier triggered cracking up to two feet long was observed on steep convex slope features in areas with and without wind effects. Plenty of snow remained on the ground and available for continued wind transport (pit profile, more info).

Avalanche Concern #1 Wind slabs

Increasing wind today combined with plenty of snow available for wind transport is expected to allow for continued wind loading today in near and above treeline terrain. Ongoing instability allowing for human triggered avalanches is expected. As wind speed increases this afternoon, isolated natural avalanche activity will remain possible in the most heavily wind loaded areas on NW-N-NE-E aspects. With the layer of lower density snow near the base of the storm snow, avalanches involving nearly all of the accumulated storm snow are possible.

Avalanche Concern #2 Storm Slabs

Instability associated with the density inversion near the base of the storm snow is likely short lived in wind sheltered areas. Some lingering instability may remain today in wind sheltered areas, but widespread instability is not expected as compared to wind affected areas. Something to keep an eye out for is the possibility of faceted snow forming at the base of the storm snow. The wet snow and refreezing rain crust below the storm snow is much warmer than the overlying storm snow. Many of the right ingredients are in place for faceting and weakening of snow just above the recently formed rain crust to occur. While this may or may not happen, it is worth keeping an eye on as faceting could contribute to instability in steep wind protected areas below treeline as this storm cycle continues.

 

The bottom line:

Near and above treeline, isolated pockets of CONSIDERABLE avalanche danger exist on NW-N-NE-E aspects on slopes 35 degrees and steeper. For all other open wind affected areas, MODERATE avalanche danger exists on slopes 35 degrees and steeper. An increase in avalanche danger with likely natural avalanche activity is expected overnight tonight into tomorrow morning.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	13 to 19 deg. F.
Max. temperature in the last 24 hours:	21 to 24 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	31 mph
Maximum wind gust in the last 24 hours:	64 mph
New snowfall in the last 24 hours:	2 to 8 inches
Total snow depth:	14 to 52 inches

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

For 7000-8000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Cloudy skies with scattered snow showers late in the morning. Increasing chances of snow in the afternoon.	Cloudy skies with high intensity snowfall at times.	Cloudy skies with high intensity snowfall at times.
Temperatures:	25 to 32 deg. F.	15 to 22 deg. F.	22 to 29 deg. F.
Wind direction:	SW	SW	W
Wind speed:	30 to 40 mph with gusts to 50 mph. Gusts increasing to 60 mph in the afternoon.	30 to 40 mph with gusts to 60 mph.	15 to 25 mph with gusts to 40 mph.
Expected snowfall:	Up to 2 in.	8 to 14 in.	8 to 16 in.
For 8000-9000 ft:
	Sunday:	Sunday Night:	Monday:
Weather:	Cloudy skies with scattered snow showers late in the morning. Increasing chances of snow in the afternoon.	Cloudy skies with high intensity snowfall at times.	Cloudy skies with high intensity snowfall at times.
Temperatures:	22 to 27 deg. F.	13 to 20 deg. F.	18 to 25 deg. F.
Wind direction:	SW	SW	W
Wind speed:	45 to 55 with gusts to 75 mph. Gusts increasing to 85 mph in the afternoon.	50 to 60 mph with gusts to 90 mph. Gusts decreasing to 80 mph after midnight.	25 to 35 mph with gusts to 55 mph. Gusts decreasing to 45 mph in the afternoon.
Expected snowfall:	Up to 2 in.	10 to 14 in.	10 to 16 in.