THIS AVALANCHE ADVISORY EXPIRED ON February 12, 2017 @ 6:59 am
Avalanche Advisory published on February 11, 2017 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on steep slopes at all elevations due to wind slabs formed during the storm and new wind slabs formed by the NE and E winds today. Human-triggered wind slab avalanches will remain possible today. Identify areas where wind slabs may exist and plan backcountry travel routes to avoid wind-loaded slopes.  

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
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    Historic
    Very Large
    Large
    Small

Human-triggered wind slab avalanches will remain possible on wind-loaded slopes 35 degrees and steeper today. As the winds shift to the east and increase, some new wind slabs will form on NW-W-SW-S-SE aspects. These new wind slabs should remain small and not extend very far from ridgelines unless wind speeds climb higher than forecasted. These east winds will strip some snow away from the wind slabs that formed during the storm, but these older wind slabs will still linger on many NW-N-NE-E-SE aspects. In some areas, these may become hard slabs that could break above a person on the slope. The largest and most fragile wind slabs will exist on wind-loaded near and above treeline terrain, but wind slabs may still be possible in some exposed below treeline areas as well. Large unstable cornices exist above many wind-loaded slopes. 

Looks for signs of recent wind-loading such as cornices, blowing snow, wind drifts, wind pillows, ripples on the snow surface, and other wind created textures to help identify where wind slabs may exist and use this information to avoid areas with possible wind slabs.

recent observations

Observations yesterday on Andesite Peak and Powderhouse Peak found up to 18 inches of new snow sitting on top of wet rain-soaked snow from earlier in the storm. Snowpit data and observations in sheltered terrain on Powderhouse Peak and on exposed wind-loaded terrain on Andesite Peak showed a right side up snowpack with more dense snow near the base of the storm snow and lighter snow near the top. On Andesite Peak, ski cuts and ski kicks triggered some shooting cracks on wind-loaded test slopes, but neither ski cuts nor large cornice pieces dropped onto test slopes produced wind slab failures. 

Weather and CURRENT CONDITIONS
weather summary

Another 6 to 12 inches of snow fell across the forecast area yesterday with areas south of Emerald Bay receiving the most new snow. Snowfall tapered off during the night and some clearing occurred. While most of the precipitation has ended, some snow showers could continue in the mountains this morning especially in areas south of Hwy. 50.  The winds have shifted to the east and northeast as a high-pressure ridge builds over the area. These winds should increase today and tonight before decreasing tomorrow once the ridge has settled over the region. This high-pressure will bring sunny skies and warmer temperatures to the mountains and inversion conditions in the valleys for the next few days. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 17 to 21 deg. F.
Max. temperature in the last 24 hours: 31 to 34 deg. F.
Average wind direction during the last 24 hours: SW-SE shifting to ENE after midnight
Average wind speed during the last 24 hours: 35 mph decreasing after midnight to 15 mph
Maximum wind gust in the last 24 hours: 79 mph
New snowfall in the last 24 hours: 6 to 12 inches
Total snow depth: 126 to 169 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy with isolated snow showers Clear Sunny
Temperatures: 29 to 34 deg. F. 14 to 20 deg. F. 35 to 40 deg. F.
Wind Direction: East East Variable
Wind Speed: Light in the morning increasing to 10 to 15 mph with gusts to 25 mph in the afternoon 10 to 15 mph with gusts to 40 mph in the evening decreasing overnight Light
Expected snowfall: 0 with a slight chance of up to 1 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy with isolated snow showers Clear Sunny
Temperatures: 25 to 30 deg. F. 15 to 20 deg. F. 33 to 38 deg. F.
Wind Direction: Northeast Northeast East
Wind Speed: 10 to 15 mph with gusts to 25 mph increasing to 20 to 25 mph with gusts to 40 mph in the afternoon 20 to 30 mph with gusts to 45 mph 15 to 20 mph with gusts to 40 mph
Expected snowfall: 0 with a slight chance of up to 1 in. 0 in. 0 in.
Disclaimer

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.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258