THIS AVALANCHE ADVISORY EXPIRED ON December 10, 2016 @ 6:54 am
Avalanche Advisory published on December 9, 2016 @ 6:54 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger exists throughout the forecast area due to wind slabs and persistent slab problems.  Wind slabs are possible on NW-N-NE-E-SE aspects near and above treeline at elevations above 8500'.  Persistent slabs are possible on North aspects along the Sierra Crest and in the Mt. Rose area.  Avalanche danger is expected to rise as another storm impacts our region tonight and through Saturday.

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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SW winds have been in the strong to gale force range overnight at higher elevations and will continue through today ahead of our next approaching storm.  Wind slabs will be possible on NW-N-NE-E-SE aspects near and above treeline at elevations above 8500'.  Below around 8500', rain soaked surface snow will prevent most blowing snow from occurring.  These wind slabs are expected to occur on slopes steeper than 37 degrees. 

Look for blowing snow, cornice formation, snow surface scouring and wind pillows as clues to where wind slabs may be forming.   

Avalanche Problem 2: Persistent Slab
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Recent snowpack tests and observations continue to show weakness on a faceted layer buried 1 to 3 feet deep near the base of the snowpack.  We have a slight break in the weather today before another storm system will impact the region tonight and tomorrow.  Snowpack tests are indicating it will be possible for this weak layer to fail and cause avalanches with additional load.  This weak layer is found on North aspects along the Sierra Crest above about 8300' and in the Mt. Rose area above about 9300'. 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 and informal observations may not supply much useful information.  Evaluate and select terrain carefully.  Avoid run out zones and pay attention to locations of up tracks and regrouping areas.

 

recent observations

Observations from Andesite Peak (Donner Summit area) and Blue Lakes (Carson Pass area) both showed warm temperatures and rain soaked surface snow at elevations below 8500'.   New snow amounts were limited to 4 to 6'' of mostly wet rain saturated snow.  No signs of instabilities were observed at these locations.

Observations from Tamarack Peak (Mt. Rose area) showed 6 to 8'' of new snow in this area at elevations above around 9000'.  Blowing snow was observed with small dense wind slabs forming along ridges.  Wind slabs were sensitive enough to be intentionally triggered by a skier.  Snowpit observations targeting the buried facet layer continued to show weakness.  Snowpack tests showed that propagation was possible along this weak layer and that the additional recent storm load may be starting to overload the weak layer.

Weather and CURRENT CONDITIONS
weather summary

Active weather is expected to continue throughout the weekend and into next week.  Chance of rain today with increasing SW winds gusting near 100mph over the higher ridges and peaks.  Remote sensors along the Sierra Crest from 8500' to 8800' are showing near to above freezing temperatures early this morning.  Most precipitation over the last 24 hours fell as rain below 8500'. 

A weak to moderate atmospheric river will move into our area tonight and through Saturday.  Snow levels will start in the 8000-9000' range with 1.5 to 2'' of liquid precipitation possible.  Most snow will be limited to above 8500-9000'.  The heaviest precipitation is forecasted to occur early Saturday morning through early afternoon.  A break in storms is expected Sunday into Monday before another atmospheric river impacts the area on Monday night.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 32 to 33 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 50 mph
Maximum wind gust in the last 24 hours: 100 mph
New snowfall in the last 24 hours: 0 to trace inches
Total snow depth: 13 to 24 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Cloudy. Chance of rain and snow in the morning. Rain likely in the afternoon. Cloudy. Chance of rain in the evening, then chance of rain and snow after midnight. Cloudy. Rain with a chance of snow.
Temperatures: 37 to 42 deg. F. 28 to 33 deg. F. 41 to 46 deg. F.
Wind Direction: SW SW SW
Wind Speed: 20 to 30mph with gusts to 65mph. 25 to 35mph with gusts to 75mph. 20 to 30 mph. Gusts to 60mph increasing to 70mph in the afternoon.
Expected snowfall: 0 in. Up to 2 in. Up to 3 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Cloudy. Chance of rain or snow in the morning. Rain and snow likely in the afternoon. Cloudy. Rain and a chance of snow. Cloudy. Rain and a chance of snow.
Temperatures: 34 to 40 deg. F. 26 to 31 deg. F. 39 to 45 deg. F.
Wind Direction: SW SW SW
Wind Speed: 30 to 50mph. Gusts up to 85mph increasing to 95mph in the afternoon. 30 to 50mph with gusts to 105mph. 30 to 50mph with gusts to 105mph.
Expected snowfall: Up to 2 in. Up to 4 in. Up to 6 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