THIS AVALANCHE ADVISORY EXPIRED ON December 9, 2016 @ 6:55 am
Avalanche Advisory published on December 8, 2016 @ 6:55 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists as additional loading of snow and rain occur throughout the region.  Wind slabs will be possible on NW-N-NE-E-SE aspects near and above treeline.  Storm slabs will be possible on all aspects below treeline and near treeline where previous snow coverage existed.  Persistent slab avalanches will become possible on N aspects along the Sierra Crest and in the Mt. Rose area.  Dangerous avalanche conditions exist.  Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.

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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Strong to gale force SW winds and new snow will make it possible for wind slabs to form throughout today.  Wind slabs could exist on NW-N-NE-E-SE aspects near and above treeline.  These wind slabs will be possible on slopes steeper than 37 degrees.  As warming occurs throughout the day, it will further the problem that these wind slabs will be much more dense than the underlying snow beneath.

Look for clues for wind slab development such as blowing snow, cornice formation, and wind pillows.  Avoid slopes with active wind loading.

Avalanche Problem 2: Storm Slab
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Storm slabs will develop on all aspects in below treeline and near treeline terrain on slopes steeper than 37 degrees.  New snow followed by a warm transition sometime today will make an upside down new snow layer with the heavy dense snow on top and lighter snow beneath.  Rain level is forecasted to rise up to at least 8000' by this afternoon.  Depending on how high it rains and amounts, avalanches could have wet slab and wet loose avalanche characteristics.

Most slopes with enough previous snow for travel will have this avalanche problem through today.  It should be easy to feel or see any large density changes within the new storm snow. Cracking around skis, shooting cracks, and rain on new snow will all be red flags and show that there is cohesion in this new storm slab layer.

Avalanche Problem 3: Persistent Slab
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Persistent slab avalanches will become possible today as heavy loading of snow and rain occurs to the snowpack.  The potential weak layer is faceted snow that exists near the base of the snowpack usually on top of a ground level ice layer.  This weak layer is found on North aspects along the Sierra Crest above about 8300' and in the Mt. Rose area above about 9300'.  The faceted layer is buried anywhere from 1 to 3 feet deep in the snowpack.  Slopes 32 degrees and steeper are the main concern for this avalanche problem.

Any avalanche activity associated with this persistent slab problem would have large consequences.  These avalanches could be remotely triggered from connected terrain.  Informal observations may not supply much useful information.  Advanced terrain management skills are needed today to safely navigate and avoid this avalanche problem.

 

 

recent observations

Observations made on Relay Peak and Tamarack Peak (Mt. Rose area) continue to show ongoing concerns for a potential persistent slab avalanche problem.  Snowpack tests at several different aspects, elevations, and locations showed that the main concern are north aspects above 9300' in the Mt. Rose area.  Similar snowpack layering existed with a weak faceted layer of snow buried near the base of the snowpack just above a basal ice layer.  This faceted layer was showing failure with PST's that indicated propagation was possible.

Weather and CURRENT CONDITIONS
weather summary

An unsettled weather pattern will continue for the forecast area through the weekend and into next week.  Several atmospheric rivers will be impacting our region that will have snow levels fluctuating and as high as 8000-9000'.  We received 5 to 11'' of new snow overnight above 8000' with 4 to 6'' of new snow forecasted through today at the higher elevations.  This current storm will switch from snow to rain sometime in the late morning/early afternoon hours as warm air moves into the area.  Rain is expected up to at least 8000' by the afternoon with increasing southwest winds into the gale force range. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 27 to 32 deg. F.
Max. temperature in the last 24 hours: 29 to 30 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 30 to 45 mph
Maximum wind gust in the last 24 hours: 77 mph
New snowfall in the last 24 hours: 5 to 11 inches
Total snow depth: 13 to 23 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 changing to rain in the afternoon. Cloudy. Rain and snow. Cloudy. Rain likely.
Temperatures: 37 to 42 deg. F. 31 to 36 deg. F. 37 to 42 deg. F.
Wind Direction: SW SW SW
Wind Speed: 10 to 15mph with gusts to 45mph increasing to 20 to 30mph with gusts to 50mph in the afternoon. 20 to 35mph with gusts to 65mph. 20 to 30mph. Gusts to 50mph increasing to 65mph in the afternoon.
Expected snowfall: 4 to 6 in. 0 in. Up to 1 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy. Snow and rain through the day. Cloudy. Snow and rain. Cloudy. Snow and rain likely.
Temperatures: 35 to 41 deg. F. 30 to 35 deg. F. 34 to 40 deg. F.
Wind Direction: SW SW SW
Wind Speed: 30 to 40mph. Gusts up to 70mph increasing to 90mph in the afternoon. 30 to 40mph with gusts to 90mph. 30 to 40mph with gusts to 90mph.
Expected snowfall: 4 to 6 in. 1 to 3 in. Up to 2 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