THIS AVALANCHE ADVISORY EXPIRED ON January 6, 2017 @ 6:55 am
Avalanche Advisory published on January 5, 2017 @ 6:55 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists at all elevations throughout the forecast area.  Dangerous avalanche conditions continue due to wind slabs, storm slabs, and deep slab avalanche problems.  Human triggered avalanches are likely and natural avalanches are possible 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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Wind slabs will continue to be a problem with additional new snow and wind throughout today.  These wind slabs will be most problematic on NW-N-NE-E-SE aspects and potentially S aspects as the winds shift towards the West today.  Natural wind slab avalanches occurred yesterday and that is expected to continue through today.

Look for areas of blowing snow, cornice formation, and wind pillows to identify where wind loading is occurring and subsequent wind slab development.  Avoid wind loaded terrain and avalanche run out zones below wind loaded terrain.

Avalanche Problem 2: Storm Slab
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Total storm snow this week is 4+ feet throughout the forecast region above 7000'.  Weaknesses within this recent storm snow will continue to be a problem for today.   There have been large fluctuations in temperatures throughout this storm cycle that have caused some areas to have an "upside down" structure.   These storm slabs will be in mostly protected areas in below treeline and near treeline terrain on all aspects.

Avalanche Problem 3: Deep Slab
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Deep slab avalanches continue to be possible on weaknesses within the old snow that is buried anywhere from 4 to 8+ feet deep below the snow surface.  Layers of concern are developed near crust facets that are near the Dec. 15 rain crust and old near surface facets at the base of the storm snow.  Any avalanches that either initially fail on or step down to these weak layers will be large and destructive.  This deep slab avalanche problem is possible on W-NW-N-NE-E aspects at all elevations.  

recent observations

Observations were made and received yesterday from Andesite Ridge (Donner Summit area) and Waterhouse Peak (Luther Pass area).  Several natural wind slab avalanches were observed in the Andesite Ridge area.  These avalanches occurred on N-NE-E aspects, 35 degrees or steeper, in near treeline terrain, with crowns up to 3' deep.  These avalanches were failing within the recent storm snow.  There was a noticeable density change within the more recent storm snow with a upside down structure.  On Waterhouse Peak, cracking and whumpfing was observed throughout the area.  Snow level was around 7000' mid morning with 2''/hour snow accumulation throughout the day.  A PST on the near crust facets near the Dec. 15 rain crust, now buried 3 to 4 feet deep, indicated that this layer is still capable of producing avalanches.

Weather and CURRENT CONDITIONS
weather summary

Colder air with snow showers are expected throughout the day with 2 to 5'' of snow forecasted above 7000'.  Winds should shift to the West and begin to taper later this afternoon/evening.  A break between storms is expected Friday with cold temperatures.  A strong atmospheric river will impact the area from Saturday through Monday.  Up to 12 inches of liquid water is forecasted along the Sierra Crest with snow levels up to 8500-9000'.  Flood impacts are expected.   

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 19 to 22 deg. F.
Max. temperature in the last 24 hours: 34 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 35 to 40 mph
Maximum wind gust in the last 24 hours: 87 mph
New snowfall in the last 24 hours: 14 to 23 inches
Total snow depth: Along the Sierra Crest 61 to 77 inches | In the Mt. Rose area 104 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 showers in the morning then snow showers in the afternoon. Mostly cloudy then becoming partly cloudy. Isolated snow showers in the evening. Sunny then becoming partly cloudy.
Temperatures: 25 to 30 deg. F. 1 to 11 deg. F. 29 to 34 deg. F.
Wind Direction: SW
Wind Speed: 10 to 15mph with gusts to 45mph. Light winds. Gusts up to 25mph in the evening. Light winds.
Expected snowfall: 2 to 5 in. Up to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow showers in the morning then snow showers in the afternoon. Mostly cloudy then becoming partly cloudy. Isolated snow showers in the evening. Sunny then becoming partly cloudy.
Temperatures: 23 to 29 deg. F. 6 to 12 deg. F. 27 to 32 deg. F.
Wind Direction: W S SW
Wind Speed: 20 to 40mph. Gusts up to 85mph decreasing to 75mph in the afternoon. 10 to 15mph. Gusts to 45mph decreasing to 30mph after midnight. Light winds becoming SW 10 to 15mph with gusts to 35mph in the afternoon.
Expected snowfall: 2 to 6 in. Up to 1 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