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.

The snowfall and winds started earlier than forecasted yesterday with 4-6 inches of heavy, 18-22% density snow accumulating before 6pm and winds averaging between 40 and 100 mph along the ridgetops starting at 9am. Overnight, another 1-2 inches of snow accumulated, and the winds remained strong out of the southwest. By 10 pm most of the snowfall had ended. This morning the winds have started to decrease into the 30's as the low pressure departs the area. Today the winds should continue to decrease before picking back up tomorrow as another strong, cold low pressure approaches the region. Some isolated snow showers could linger over the Sierra today as well. By tomorrow afternoon expect more widespread snowfall to start again as the next storm hits the area.

Observations:

Avalanche activity due to failure of wind slabs formed by yesterday's strong southwest winds occurred on Talking Mountain (Echo Summit area - photo), on Castle Peak (Donner Summit area - photo), and on Tamarack Peak (Mt. Rose area - video and photos). In all three of these areas, the slides occurred on 36-44 degree, N-NE facing, wind-loaded slopes in near and above treeline terrain. The slabs ranged from 4 inches to 16 inches in thickness. Debris from these slides ran downhill for anywhere from 60 ft. to 200 ft. The interface between the soft snow that fell on March 30th and the stiff, newly-formed wind slabs served as the weak layer for all of these slides. On Castle Peak and on Talking Mountain these slides failed naturally. On Tamarack Peak a skier triggered the avalanches while standing 15-20 ft away in lower angle terrain on a ridgeline. Skier triggered shooting cracks occurred on Castle Peak and on Tamarack Peak as well.

Avalanche concern #1: Wind Slabs

New snow and strong winds yesterday and overnight created larger winds slabs and tender cornices on wind-loaded slopes over the last 24 hours. Human triggered avalanches involving these new wind slabs will be probable today. Some natural avalanches due to failure of these wind slabs will be possible in the most heavily wind-loaded areas as well. These stiff slabs could be triggered from lower angle slopes and could pull snow from those lower angle slopes down with them. The most likely areas for avalanches will be on wind-loaded NW-N-NE-E aspects in near and above treeline terrain. However, some unstable wind slabs could exist on lower elevation slopes due to the strong winds. Careful snowpack observations can help determine where slabs have formed and where they have not. The best recreation and safest conditions will be on slopes where slabs have not formed and the snow remains soft.

Avalanche concern #2: Storm snow instabilities

Yesterday's heavy storm snow sits on top of lighter older snow. In some areas this storm snow may not have bonded well to the snow from March 30th. Adding a person or a snowmobile to the snowpack may be enough to break the bonds at this interface today on slopes steeper than 35 degrees even in non-wind affected areas. Most of these avalanches should only involve the new snow and should have more soft slab characteristics. These types of instabilities will be most likely in steep open areas.

The bottom line:

Near and above treeline pockets of CONSIDERABLE avalanche danger exist on the wind-loaded, NW-N-NE-E aspects 35 degrees and steeper with MODERATE avalanche danger on the other aspects. Below treeline pockets of MODERATE avalanche danger exist on all aspects on slopes steeper than 35 degrees. 

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	18 deg. F.
Max. temperature in the last 24 hours:	26 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	55-65 mph
Maximum wind gust in the last 24 hours:	137 mph
New snowfall in the last 24 hours:	5-8 inches
Total snow depth:	107-163 inches

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

For 7000-8000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Mostly cloudy with a 20% chance for isolated snow showers.	Mostly cloudy with a 20% chance of snow showers.	Snow likely
Temperatures:	25-32 deg. F.	17-23 deg. F.	23-28 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	10-20 mph with gusts to 40 mph decreasing to 25 mph in the afternoon	10-15 mph with gusts to 30 mph	10-20 mph with gusts to 35 mph increasing to 20-30 mph with gusts to 60 mph
Expected snowfall:	trace in.	trace in.	up to 2 in.
For 8000-9000 ft:
	Saturday:	Saturday Night:	Sunday:
Weather:	Mostly cloudy with a 20% chance for isolated snow showers.	Mostly cloudy with a 20% chance of snow showers.	Snow likely
Temperatures:	23-27 deg. F.	10-17 deg. F.	21-27 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	20-35 mph with gusts to 55 mph decreasing to 15-25 mph with gusts to 35 in the afternoon	20-30 mph with gusts to 50 mph	15-25 mph with gusts to 50 mph increasing to 25-40 mph with gusts to 70 mph in the afternoon
Expected snowfall:	trace in.	trace in.	up to 2 in.