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.

A strong winter storm has arrived over the forecast area. The southwest winds began increasing yesterday ahead of this storm and have continued to gain strength through this morning. Since yesterday these winds have averaged 35-55 mph along the mountain ridges with gusts as high as 98 mph. Snowfall started with the arrival of the storm last night. So far 6 to 12 inches of snow has accumulated in areas above 7000 ft north of Emerald Bay. South of Emerald Bay only 3 to 6 inches of new snow has fallen. Snowfall should continue through tomorrow with the most intense period of snow occurring before 2pm today. The forecast calls for snowfall rates of 2 to 3 inches per hour through noon today. By tomorrow afternoon snow totals around the forecast area could reach 2-4 feet above 7000 ft and up to 2 feet at Lake level. The highest snowfall amounts should occur north of Hwy. 50 with slightly less snow accumulating south of Hwy. 50. The winds should remain strong today with average speeds above 50 mph at all elevations above 7000 feet and gusts along the Sierra Ridges approaching 115 mph. Tonight these winds should decrease slightly before increasing again tomorrow. Click here for a weather briefing from the Reno NWS.

Recent Observations:

Several natural avalanches occurred yesterday due to newly formed winds slabs overloading Monday's cold light snow. On Silver Peak (photos) and on the far east ridge of Tamarack Peak (photos) these slides had crowns approximately 1 foot deep and ranged from 50 to 100 feet wide. All of these avalanches happened in areas where heavy wind loading was occurring on NE aspects above treeline on 35-40 degree slopes. Natural cornice collapses seemed to trigger most of these slides. In the Silver Peak area (photos, more info), in the Tamarack Peak area (photos, video, more info), and near Round Top on Carson Pass (video, more info), strong winds continued to transport snow and create new wind slabs all day yesterday on leeward slopes near and above treeline. Skier triggered shooting cracks occurred in all three of these areas on newly wind loaded slopes. Snow stability tests also indicated that the bonds between the winds slabs and the light snow below them remained weak. Once those bonds broke fractures traveled quickly and easily travel through the snowpack. Below treeline where less wind existed small skier triggered sluffs involving the top 6 inches of Monday's snow occurred on steep test slopes in the Tamarack Peak and Silver Peak areas. In all of three of these areas, the persistent weak layer of crusts and facets that has plagued the region since January still exists. While Monday's snow and yesterday's wind loading did not provide enough load to re-awaken this layer, observations showed that it could easily become an issue once more snow accumulates.

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

The wind slabs that started to form yesterday have only grown larger, more widespread, and more fragile due to the additional wind and snow impacting the region. These slabs will keep increasing in size and extent as long as this winter storm continues. These slabs rest on top of a at least two potential weak layers: Monday's light low density snow and the Jan. crust/facet combination. Widespread natural avalanches caused by these wind slabs overloading the snow below them will be likely today. Avalanches that start due to the wind slabs failing could step down to the lower crust/facet weak layer in areas where the wind slabs exist on top of the crust/facet layer. Avalanches involving the newly formed winds slabs could be large, deep, and travel long distances regardless of whether or not these avalanches step down to the lower weak layer. N-NE-E aspects near and above treeline will likely hold the largest of these wind slabs; however, dangerous wind slabs will also exist on cross-loaded NW and SE aspects as well as open wind affected areas below treeline due to the high wind speeds at all elevations. New soft slabs will also form in less wind affected areas today as more snow accumulates across the forecast area. These soft slabs could break loose in response to the additional weight of a person on the slopes. Open slopes below treeline will hold the best potential for this kind of instability. 

Today's Secondary Avalanche Concern: Persistent Deep Slabs

The persistent weak layer of crusts and facets that exists within the upper half of snowpack remains weak. The new snow, soft slabs, and wind slabs accumulating on top of it will will likely be enough to cause it to break in some areas today. 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 both near and below treeline.

The bottom line:

Near and above treeline HIGH avalanche danger will develop on NW-N-NE-E aspects, on slopes 35 degrees and steeper. Areas of  HIGH avalanche danger may also form near and below treeline on NW-N-NE aspects steeper than 35 degrees. CONSIDERABLE danger exists on all other aspects. Dangerous natural and human-triggered avalanches are likely today due to high winds, intense snowfall, and a weak snowpack. Travel in or near avalanche terrain is not recommended.

Andy Anderson - Avalanche Forecaster, Tahoe National Forest

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

0600 temperature:	17-22 deg. F.
Max. temperature in the last 24 hours:	18-28 deg. F.
Average wind direction during the last 24 hours:	Southwest
Average wind speed during the last 24 hours:	35-55 mph
Maximum wind gust in the last 24 hours:	98 mph
New snowfall in the last 24 hours:	North of Emerald Bay 6-13 inches | South of Emerald Bay 3-6 inches
Total snow depth:	28-54 inches

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

For 7000-8000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Snow with the most intense snowfall occurring before noon	Cloudy with snow showers	Cloudy becoming mostly cloudy in the afternoon. Snow showers likely.
Temperatures:	20-27 deg. F.	8-15 deg. F.	19-26 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	50-60 mph with gusts to 90 mph decreasing to 80 mph in the afternoon	35-45 mph with gusts to 60 mph	35-45 mph with gusts to 65 mph
Expected snowfall:	8-16 in.	5-10 in.	4-8 in.
For 8000-9000 ft:
	Wednesday:	Wednesday Night:	Thursday:
Weather:	Snow with the most intense snowfall occurring before noon	Cloudy with snow showers	Cloudy becoming mostly cloudy in the afternoon. Snow showers likely.
Temperatures:	21-27 deg. F.	4-11 deg. F.	18-24 deg. F.
Wind direction:	Southwest	Southwest	Southwest
Wind speed:	75-85 mph with gusts to 115 mph decreasing to 60-70 mph with gusts to 95 mph in the afternoon	50-60 mph with gusts to 85 mph decreasing to 40-50 mph with gusts to 75 mph after midnight	50-60 mph with gusts to 85 mph increasing to 65-75 mph with gusts 100 mph in the afternoon
Expected snowfall:	10-18 in.	6-12 in.	4-8 in.