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.

24 to 40 inches of new snow fell across the forecast area since Feb 28th. The largest accumulations occurred in the northern half of the forecast area. This new snow doubled the snow depth in many areas. The winter storm that brought all of this snow departed the region last night. As it left, the winds shifted to the east and decreased. These east winds should increase today as a high pressure ridge builds over the area. This ridge will bring sunny clear weather and slightly warmer temperatures to the region today. Daytimes highs should reach into the mid 30's above 7000 ft. By tomorrow the east winds should decrease and temperatures should climb another 5-10 degrees above today's highs. 

Recent Observations:

Yesterday a tragic avalanche incident occurred near Stanford Rocks resulting in the death of the skier who triggered it. Initial reports indicate that this skier triggered slide occurred on a steep NE facing, wind loaded slope. The slide began due to a failure within the storm snow, but it then stepped down to a lower weak layer resulting in a deeper more severe avalanche (more info, photos). Farther south along on Hidden Peak, a natural avalanche one to two feet deep and about 100 feet wide occurred due to heavy wind loading on a NE facing, 38 degree, near treeline slope. This slide likely occurred yesterday morning. It ran down slope about 150-200 vertical feet.

Observations from Hidden Peak (photos, video, more info), Becker Peak (videos, more info), and Tamarack Peak (photo, videos, more info) all showed several minor weaknesses within the new snow as well as two more serious deeper weaknesses. Ski cuts on test slopes resulted in shooting cracks and collapsing on wind loaded slopes at all elevations in Tamarack Peak area and on Hidden Peak. Snowpit data showed that the deeper weaknesses in the snowpack still remain active in all three of these areas (videos from Becker Peak, videos from Tamarack Peak, video from Hidden Peak). Moderate force would initiate a fracture at the density inversion between Monday's light snow and the heavier more wind affected snow that has fallen since Wednesday morning. Once initiated, these fractures could still travel easily along this interface. The Jan. crust/facet combination represented the other main weakness. While it took more force to break this layer, tests showed that fractures could travel along this persistant weak layer as well.  Strong winds continued to affect most open slopes both above and below treeline in these areas yesterday causing the recently form winds slabs to become more widespread and larger. The thickest wind slabs existed on N-NE-E aspects in near and above treeline terrain. 

Today's Primary Avalanche Concerns: Wind Slabs and Storm Slabs

Shifting winds and lots of snow available for transport will create complex wind loading and dangerous wind slabs will also exist on a variety of slopes today. As the east winds increase today, they will transport snow away from the SE-E-NE aspects and onto the NW-W-SW aspects. This will create new wind slabs on the NW-W-SW aspects and could add snow to N and S aspects by cross-loading those slopes. The scouring that occurs on the NE-E-SE aspects will also compact the snow on these aspects leaving behind hard wind slabs. Both today's new wind slabs and the wind slabs left over from the storm will remain fragile today. Adding a person on top of these slabs will likely result in an avalanche. Avalanches resulting from the wind slabs on the SW-W aspects will likely remain smaller due to the fact that these new wind slabs should not grow very large today. Avalanches involving the wind slabs on the NW-N-NE-E aspects could be large, deep, and travel long distances. They could also step down to the lower weak layers mentioned above. Open wind affected areas below treeline should still hold some fragile wind slabs as well.

The slightly heavier snow that fell since Wednesday morning could act as a soft slab in less wind affected areas. Since the previously mentioned weaknesses still exist in these areas, human triggered soft slab avalanches will also remain likely today on steep open slopes near and below treeline especially on NW-N-NE aspects.

Today's Secondary Avalanche Concern: Persistent Deep Slabs

The persistent weak layer of crusts and facets that exists below the recent snow remains weak. As the new snow above it consolidates into more of a slab layer, breaking this deeper persistent weak layer could become easier. Human triggered avalanches resulting from failure of this layer will remain likely. Any avalanches that occur today could easily step down into this layer making the resulting avalanches deeper and even more dangerous. Observations made around the forecast area over the past week have shown that this weak layer remains on NW-N-NE aspects in near and below treeline areas.

Today's Third Avalanche Concern: Warming Instabilities

The strong March sun and daytime highs above freezing could cause enough warming to create some instabilities on the sun-exposed SE-S-SW aspects. Cross loaded SE facing gullies and newly wind loaded S-SW aspects at all elevations will hold the best potential for this kind of instability. While most of these warming instabilities remain limited to roller balls, pinwheels, and point release slides, some slab avalanches could occur on these aspects due to the rapidly changing conditions.

The bottom line:

CONSIDERABLE avalanche danger remains on NW-N-NE-E aspects on slopes 35 degrees and steeper at all elevations with pockets of CONSIDERABLE danger on the below treeline E and SE aspects. MODERATE avalanche danger exists on the S-SW-W aspects. Dangerous human-triggered avalanches remain likely today due to complex wind loading, recent snow, and a weak snowpack.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	7-11 deg. F.
Max. temperature in the last 24 hours:	19-25 deg. F.
Average wind direction during the last 24 hours:	Southwest shifting to east last night
Average wind speed during the last 24 hours:	Southwest: 40 mph | East: 25-30 mph
Maximum wind gust in the last 24 hours:	82 mph
New snowfall in the last 24 hours:	2-9 inches
Total snow depth:	34-61 inches

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

For 7000-8000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Sunny	Clear	Sunny
Temperatures:	31-38 deg. F.	19-28 deg. F.	40-47 deg. F.
Wind direction:	East	East	Variable
Wind speed:	35-45 mph with gusts to 60 mph	15-20 mph with gusts to 30 mph	Light
Expected snowfall:	O in.	O in.	O in.
For 8000-9000 ft:
	Friday:	Friday Night:	Saturday:
Weather:	Sunny	Clear	Sunny
Temperatures:	30-34 deg. F.	23-32 deg. F.	39-43 deg. F.
Wind direction:	East	East	East
Wind speed:	40-50 mph with gusts to 70 mph	20-30 mph with gusts to 50 mph	15-20 mph with gusts to 30 mph in the morning decreasing in the afternoon
Expected snowfall:	O in.	O in.	O in.