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.

Snow levels are falling rapidly this morning after peaking last night at nearly 9,000' in some areas. So far this warm storm system has brought 14 to 24 inches of high density snow from 2 to 4.5 inches of water at the 8,200' to 8,700' level over the past two days. Greater new snow amounts likely exist above 9,000'. One more burst of high intensity snowfall is possible before 10 am this morning before snowfall intensity decreases to light showers for the remainder of the day. Ridgetop winds remain strong in speed this morning after gusts peaked over 100 mph with cold front passage around 3 am. Moderate to strong southwest to west winds are forecast to continue today. Snow shower activity is expected to continue tonight before a colder and dryer storm system reaches the forecast area tomorrow afternoon. Ridgetop winds are forecast to return to gale force out of the southwest as the next system arrives tomorrow.

Observations:

Observations made yesterday on Castle Peak (Donner Summit area) and near Grouse Rock (Blackwood Canyon area) revealed that around 4 to 8 inches of new snow had accumulated above 7,500' by mid day. Wind loaded areas held wind pillows 12 to 18 inches deep in near treeline terrain. New snow had bonded fairly well to the prominent crust at the base of the storm snow. Minimal evidence of instability was observed in both areas at that time, with only minor cracking less than 1 foot long from skier loading of wind pillows. Snowpit data yielded little additional evidence of instability with test results indicating that propagation was unlikely along weak layers within the new snow or along faceted snow crystals on the top or bottom of the prominent rain crust that formed on Dec 28-29 (pit profiles, photos).

All of this new snow has fallen on a variable snowpack across the forecast area. Along the Sierra Crest north of Barker Pass, this new snow has fallen on a 1 to 2 foot snowpack capped by a thick rain crust from the Dec 28-29 event. This crust has faceted snow along both it's top and bottom. Along the Sierra Crest south of Barker Pass and on the East side of Lake Tahoe, this new snow has fallen mostly on bare ground and some icy patches of old snow from either earlier this winter or held over from last winter.

Avalanche Concerns:

Significant additional amounts of rain and new snow have accumulated in these areas since yesterday. It is quite possible that a natural avalanche cycle occurred last night as rain fell on new snow and created wet snow avalanches. It is also possible that 11 to 18 inches of additional high density new snow caused dry slab avalanches as yesterday's nonreactive weak layers were overburdened by additional new snow loading overnight.

Avalanche Concern #1: Storm slabs and Wind slabs

With the addition of another 11 to 18 inches of new snow on top of the 3 to 6 inches from the day before, widespread storm slabs exist. As winds continue today, ongoing wind loading is expected to build additional wind slabs in lee areas both near and above treeline and in open areas below treeline. With rising snow levels yesterday and falling snow levels this morning, snowpack failure is expected to occur near the base of the storm snow, especially at the higher elevations that received only minimal amounts of rain or stayed above snow level throughout this event.

Avalanche Concern #2: Persistent slabs

For areas along the Sierra Crest in the northern half of the forecast area, the Dec 28-29 rain crust was covered in around inch of new snow late on Jan 16. This snow faceted a bit prior to becoming buried at the start of this storm cycle. At this time it is unknown if rising snow levels last night allowed rain to reach and destroy these facets or not. If these facets have persisted, they are a likely failure point within the snowpack as the storm snow above will gain strength faster than the facets sandwiched between the bottom of the storm snow and the top of the crust. This is anticipated to be a possible issue above 8,000' as significant rainfall has occurred at lower elevations.

The bottom line:

Near and above treeline, avalanche danger is CONSIDERABLE on NW-N-NE-E aspects on slopes 35 degrees and steeper. For all other areas, MODERATE avalanche danger exists on slopes 35 degrees and steeper. Large destructive avalanches are possible above 7,500'.

Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	23 to 29 deg. F.
Max. temperature in the last 24 hours:	34 to 37 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	52 mph
Maximum wind gust in the last 24 hours:	103 mph
New snowfall in the last 24 hours:	11 to 18 inches
Total snow depth:	14 to 52 inches

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

For 7000-8000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Cloudy skies with widespread snow showers.	Cloudy skies with isolated snow showers.	Cloudy skies with a chance of snow in the morning. Snow likely in the afternoon.
Temperatures:	19 to 26 deg. F.	12 to 19 deg. F.	25 to 32 deg. F.
Wind direction:	SW shifting to W	W shifting to SW	SW
Wind speed:	30 to 40 mph with gusts to 60 mph.	25 to 30 mph with gusts to 45 mph, decreasing to 15 to 20 with gusts to 30 mph after midnight.	30 to 40 mph with gusts to 55 mph. Gusts increasing to 70 mph in the afternoon.
Expected snowfall:	4 to 8 in.	0 to trace in.	Up to 4 in.
For 8000-9000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Cloudy skies with widespread snow showers.	Cloudy skies with isolated snow showers.	Cloudy skies with a chance of snow in the morning. Snow likely in the afternoon.
Temperatures:	14 to 21 deg. F.	10 to 17 deg. F.	20 to 27 deg. F.
Wind direction:	SW shifting to W	W	SW
Wind speed:	55 to 60 mph with gusts to 90 mph, decreasing to 35 to 40 mph with gusts to 60 mph in the afternoon.	30 to 35 mph with gusts to 55 mph, decreasing to 20 to 25 mph with gusts to 40 mph after midnight.	45 to 50 mph with gusts to 80 mph, increasing to 55 to 60 mph with gusts to 100 mph in the afternoon.
Expected snowfall:	5 to 8 in.	0 to trace in.	Up to 4 in.