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.

Yesterday's storm left about 4 inches of cold, light snow (8% density) above 7000' along the Sierra Crest. Areas east of Lake Tahoe reported only 1-3 inches of new snow. As this storm departed late last night, the winds shifted towards the NE and decreased from 35-45 mph down to 10-15 mph. Some clouds and scattered snow showers should linger over the forecast area this morning. The forecast calls for a second system to impact the forecast area tonight. The winds should shift back to the west and southwest and increase and more clouds should move into the area this afternoon as this system approaches. This storm should bring more cold air to the region and could deposit another 2-4 inches of snow above 7000' tonight. By tomorrow the winds should shift back to the northwest and decrease as this storm departs.

Observations:

Even though the snow did not start to accumulate until late yesterday afternoon, the strong southwest winds started moving old snow and building stiff wind slabs on the N-NE-E aspects in the early hours of the morning. In the Mt. Rose area these wind slabs formed on leeward slopes above and below treeline. Observations showed that the winds deposited these slabs onto a mix of soft snow, thin sun crusts, and previously wind-affected surfaces. These newly-formed wind slabs did not bond well to the surfaces below them. On the far east ridge of Tamarack Peak, a skier triggered a small avalanche (1ft crown, about 100ft wide, ran about 30-40 ft down slope) on a N-NE facing, 38 degree, test slope (photos and video) in near treeline terrain around noon. This slide failed on the interface between the newly-formed, stiff wind slab and the softer snow beneath it. Backcountry skiers also triggered avalanches on E facing slopes below treeline in the Chickadee Ridge area (Ophir Creek Drainage) by weighting the shallow edges of the newly formed wind slabs. Once the bonds holding these slabs broke the fracture propagated out into areas where the slabs had grown to be about 18 inches deep through wind loading alone. The interface between the newly formed wind slab and a thin sun crust served as the weak layer in these slides. Observations in non-wind-loaded terrain indicated a mostly stable snowpack in both of these locations in the Mt. Rose backcountry (snowpit).

Avalanche concern #1: Wind slabs

Wind slabs will remain the primary avalanche concern today. The wind slabs did not bond well to the surfaces below them yesterday. Last night's new snow and continued strong winds caused these already fragile wind slabs to increase in weight, size, and distribution. Human-triggered avalanches due to the failures of these new wind slabs will remain possible. The wind-loaded N-NE-E aspects near and above treeline will hold the largest of these wind slabs. However, wind-loaded and cross loaded NW-N-NE-E-SE aspects at all elevations could hold pockets of unstable wind slabs.  Most of these types of avalanche should only involve the newly-formed wind slabs; however, some could still step down to the Feb 19th layer in isolated areas of complex, steep terrain.

Avalanche Concern #2: Deep slabs

Very isolated areas of deep slab instability still lurk near and above treeline on pockets of very steep (over 40 degrees), rocky, complex terrain on NW-N-NE aspects where a shallow snowpack allows the Feb 19 weak layer to live closer to to the surface. Human triggered avalanche activity on this layer remains unlikely except in these very isolated pockets of extreme terrain where a trigger in the right spot on the slope could still break the bonds between this weak layer and the snow above it.

The bottom line:

Pockets of MODERATE avalanche danger exist on NW-N-NE-E-SE facing slopes steeper than 35 degrees on wind-loaded slopes at all elevations. Very isolated areas of deep slab instability linger near and above treeline on NW-N-NE aspects in rocky terrain, 40 degrees and steeper.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	12 deg. F.
Max. temperature in the last 24 hours:	23 deg. F.
Average wind direction during the last 24 hours:	Southwest shifting to the northeast after midnight last night
Average wind speed during the last 24 hours:	Southwest: 35-45 mph | Northeast 10-15 mph
Maximum wind gust in the last 24 hours:	86 mph
New snowfall in the last 24 hours:	2-4 inches
Total snow depth:	92-124 inches

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

For 7000-8000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Mostly cloudy with isolated snow showers in the morning.	Mostly cloudy with isolated snow showers in the evening. Snow likely after midnight.	Mostly cloudy with scattered snow showers in the morning. Partly cloudy with a slight chance for continued showers in the afternoon.
Temperatures:	19-24 deg. F.	10-17 deg. F.	19-24 deg. F.
Wind direction:	North shifting to the west this afternoon	Southwest	West shifting to northwest in the afternoon
Wind speed:	10-15 mph with gusts to 25 mph	10-15 mph with gusts to 35 mph	10-20 mph with gusts to 40 mph decreasing to 10-15 mph in the afternoon
Expected snowfall:	O in.	2-4 in.	O in.
For 8000-9000 ft:
	Tuesday:	Tuesday Night:	Wednesday:
Weather:	Mostly cloudy with isolated snow showers in the morning.	Mostly cloudy with isolated snow showers in the evening. Snow likely after midnight.	Mostly cloudy with scattered snow showers in the morning. Partly cloudy with a slight chance for continued showers in the afternoon.
Temperatures:	10-18 deg. F.	6-12 deg. F.	10-18 deg. F.
Wind direction:	North shifting to the west this afternoon	West shifting to the southwest	West shifting to the northwest in the afternoon
Wind speed:	10-20 mph with gusts to 30 mph	10-20 mph with gusts to 35 mph increasing to 30-50 mph with gusts to 65 mph	30-50 mph with gusts to 65 mph decreasing to 10 -15 mph with gusts to 25 mph
Expected snowfall:	O in.	2-4 in.	O in.