THIS AVALANCHE ADVISORY EXPIRED ON January 22, 2017 @ 6:58 am
Avalanche Advisory published on January 21, 2017 @ 6:58 am
Issued by Andy Anderson - Tahoe National Forest

Human triggered wind slab and storm avalanches are likely today. Natural avalanches are possible. CONSIDERABLE danger exists at all elevations. Some large and destructive avalanches could occur. Dangerous avalanche conditions exist. Carefully evaluate the snowpack and the terrain before committing to any slopes. Use this information to make conservative and cautious decisions and plan safe routes of travel that avoid avalanche problems. As another strong winter storm impacts the region tonight through Monday morning, the avalanche danger will increase.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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    Certain
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Strong S and SW winds and additional snow have added to the fragile wind slabs that already exist on wind-loaded W-NW-N-NE-E-SE aspects. While the largest and most sensitive wind slabs will exist in near and above treeline terrain, some wind slabs may also exist on wind loaded slopes in below treeline terrain. As more snow and wind impact the region today and in the next 48 hours, these wind slabs will grow larger and more widespread. Human triggered wind slab avalanches are likely today and natural wind slab avalanches are possible. Some large and destructive wind slab avalanches could occur in areas with heavy wind loading

Use blowing snow, cornices, wind drifted snow, and other wind created features and textures to identify where wind slabs may exist and avoid those areas. 

Avalanche Problem 2: Storm Slab
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    Very Likely
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Changing conditions during the storm have allowed weak layers to form within the storm snow. Human triggered storm slab avalanches will be likely today and some natural storm slab avalanches may remain possible. Any steep slopes with new snow on them hold the potential for storm slab avalanches

Clues like cracking, collapsing, and whumphing can help identify where storm slabs may exist as can digging into the snowpack with your hands or probing with a pole to look for layers in the storm snow. Use these clues to avoid steep terrain where storm slabs may exist. Storm slabs can exist on tree covered slopes in the openings between trees and may connect across some of these open spaces. 

recent observations

Widespread human-triggered wind slab avalanches occurred on Jakes Peak, Andesite Peak, and Incline Lake Peak yesterday. These avalanches had crowns ranging from 1 to 2.5 ft. They were triggered by ski cuts and small cornice pieces dropped onto the slopes. Some of them were triggered remotely. These avalanches failed within the storm snow. In addition to these wind slabs shooting cracks and unstable test results were noted on Andesite Peak in below treeline sheltered terrain. 

Weather and CURRENT CONDITIONS
weather summary

Since snowfall started on Jan. 18th the forecast area has received 30 to 50 inches of new snow above 8000 ft. Light to moderate snow showers should continue through the day with another 3 to 6 inches of snow above 7000 ft. and 4 to 8 inches above 8000 ft. Southwest winds will decrease some but remain strong enough to transport snow. This brief "lull" in the weather ends tonight as another stronger winter storm arrives over the region. South and southwest winds should increase again with gusts over 120 along the ridgetops after midnight. The gale force winds should continue through Sunday. Heavy snowfall should also start again and continue through Monday morning. The forecast calls for 5 to 10 inches tonight and another 10 to 20 inches tomorrow with similar amounts for Sunday night. Snow levels should rise some tomorrow but should not climb above 5000 ft. A winter storm warning goes into effect this afternoon and remains in effect through Monday morning. Check in with the Reno NWS for more details.

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: 23 to 27 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 35 to 50 mph
Maximum wind gust in the last 24 hours: 91 mph
New snowfall in the last 24 hours: 12 to 22 inches
Total snow depth: 106 to 134 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with snow showers Snow Heavy snow
Temperatures: 24 to 29 deg. F. 22 to 27 deg. F. 25 to 30 deg. F.
Wind Direction: Southwest South Southwest
Wind Speed: 20 to 30 mph with gusts to 50 mph 15 to 25 mph with gusts to 55 mph 20 to 35 mph with gusts to 75 mph
Expected snowfall: 3 to 6 in. 5 to 10 in. 10 to 20 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with snow showers Snow Heavy snow
Temperatures: 20 to 25 deg. F. 19 to 24 deg. F. 22 to 27 deg. F.
Wind Direction: Southwest Southwest shifting to south after midnight Southwest
Wind Speed: 25 to 40 mph with gusts to 75 mph 25 to 35 mph with gusts to 70 mph increasing to 30 to 45 mph with gusts to 120 mph after midnight 45 to 60 mph with gusts to 130 mph decreasing to 35 to 55 mph with gusts to 100 mph in the afternoon
Expected snowfall: 4 to 8 in. 5 to 10 in. 10 to 20 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