THIS AVALANCHE ADVISORY EXPIRED ON January 13, 2017 @ 6:54 am
Avalanche Advisory published on January 12, 2017 @ 6:54 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists at all elevations due to wind slab, storm slab, and deep slab avalanche problems.  Dangerous avalanche conditions exist.  Natural avalanches are possible and human triggered avalanches are likely.  Careful snowpack evaluation, cautious route finding, and conservative decision making are essential today.

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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Very large wind slabs have formed on NW-N-NE-E-SE aspects in near treeline and above treeline terrain during our recent storm cycle.  These wind slabs will remain fragile today and grow in size with additional snow and wind.  As the wind direction changes from SW to NE/E today, wind slabs will also become possible on S-SW-W-NW aspects in exposed near treeline and above treeline terrain.

Look for blowing snow, cornice formation, snow surface clues, and wind pillows as to where wind slabs are developing or have previously been developed.  Very large cornices exist along ridgelines, extra caution is advised around these hazards.  

Avalanche Problem 2: Storm Slab
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Storm slabs will be possible on all aspects in near treeline and below treeline terrain as more new snow impacts our area.  Another foot or more of snow is possible above 7000' today.  How this new snow bonds to the old snow surface and/or weaknesses within this new storm snow will be of concern today.   

Avalanche Problem 3: Deep Slab
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As our recent storm snow continues to settle and gain strength, deep slab avalanches are becoming unlikely but not impossible events.  Deep slab avalanches are characterized by failure more than 3 feet deep in the snowpack and could be large wind slabs, storm slabs or have failure deeper down in the snowpack to the Jan. 9 or Dec. 15 rain crusts.  These deep slab avalanches could occur on any aspect and at any elevation.  Areas above 9000' still represent a concern where significant rain did not affect the snowpack and the Dec. 15 facets.  While this avalanche problem is becoming unlikely, any deep slab avalanche would have severe consequences.   

recent observations

Observations were received yesterday from Negro Canyon (Donner Summit area).  Continued wind transport was observed with reactive wind slabs in the area.  Large cornices were built out along exposed ridgelines.  No signs of storm slab weakness was observed throughout the upper 4' of recent storm snow.  Snow below the Jan. 9 rain crust is still wet and has not refrozen yet.  Numerous creeks and open water existed below 6800' in this area.

 

Weather and CURRENT CONDITIONS
weather summary

A winter storm warning is in effect until 10pm tonight.  4 to 8 inches of new snow is expected through today with the possibility of over 1 foot above 7000' in some areas.  SW winds this morning will switch to NE winds during the day with cooling temperatures.  High pressure will build over the weekend with clearing skies. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 18 to 21 deg. F.
Max. temperature in the last 24 hours: 27 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: (no data available) mph
Maximum wind gust in the last 24 hours: (no data available) mph
New snowfall in the last 24 hours: 3 to 6 inches
Total snow depth: 89 to 116 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow. Cloudy. Chance of snow. Mostly cloudy then becoming partly cloudy. Chance of snow showers in the morning.
Temperatures: 20 to 25 deg. F. 11 to 17 deg. F. 24 to 29 deg. F.
Wind Direction: SW shifting to E East shifting to NE
Wind Speed: SW winds 10mph becoming E 10 to 15mph. Gusts to 25mph. East winds 10 to 15mph becoming NE 10 to 15 with gusts to 25mph after midnight. Calm winds.
Expected snowfall: Expected 5 to 10 in., Possible 10 to 14 in. Expected up to 2 in., Possible 2 to 4 in. Trace in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow Cloudy. Snow likely in the evening then chance of snow after midnight. Mostly cloudy then becoming partly cloudy. Chance of snow showers in the morning.
Temperatures: 14 to 20 deg. F. 10 to 15 deg. F. 22 to 27 deg. F.
Wind Direction: SW shifting to E NE E
Wind Speed: SW 10 to 15mph this morning becoming E 10 to 15mph with gusts to 40mph in the afternoon. 15 to 20mph. Gusts up to 25mph increasing to 40mph after midnight. 15 to 20 with gusts to 45mph.
Expected snowfall: Expected 5 to 10 in., Possible 10 to 14 in. Expected up to 2 in., Possible 2 to 4 in. Trace 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