THIS AVALANCHE ADVISORY EXPIRED ON December 17, 2016 @ 6:54 am
Avalanche Advisory published on December 16, 2016 @ 6:54 am
Issued by Steve Reynaud - Tahoe National Forest

Areas above 8000' where the most snow has fallen will have Considerable avalanche danger.  Wind slabs have and will continue to form throughout today on NW-N-NE-E-SE-S aspects.  Deep persistent slabs will be possible above 9000' on NW-N-NE aspects.  Natural triggered avalanches are possible and human triggered avalanches are likely in these areas.  Large destructive avalanches remain possible throughout today.   Firm icy surfaces exist at the lower elevations and could pose dangerous travel conditions with long sliding falls possible. 

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 have continued throughout the night and into the morning.  Above 8000' where the most new snow exists, wind slabs will be likely on NW-N-NE-E-SE aspects near and above treeline.  As the winds shift to the W today, wind slabs will also be possible on cross loaded S aspects near and above treeline.  Natural avalanche activity is possible with human triggered avalanches likely above 8000', especially in the Mt. Rose area where more new storm snow exists at higher elevations.  Wind slab avalanches on NW-N-NE aspects above 9000' will have the possibility of stepping down to the deep persistent slab weak layer and causing a very large and destructive avalanche

Pay attention to total snow depth in your area as new storm snow fluctuates greatly throughout the forecast area.  Look for blowing snow, cornice formation, snow surface scouring, and wind pillows to detect where wind slabs exist.  Avoid areas over 35 degrees in wind loaded terrain.

Avalanche Problem 2: Deep Slab
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The deep persistent slab avalanche problem we have been dealing with received a very large amount of load during this storm and triggering an avalanche on this weak layer remains possible today.  The persistent weak layer is now buried anywhere from 3 to 6+ feet deep under the snow surface.  This avalanche problem exists on NW-N-NE aspects above 9000' throughout the forecast area.  These deep persistent slabs could be triggered by smaller wind slab avalanches that step down and cause failure on the persistent weak layer.  Large destructive and unsurvivable avalanches are possible today.

Deep persistent slabs have unpredictable avalanche behavior.  These avalanches can be remotely triggered from any connected terrain.  Avalanche avoidance, cautious route finding and conservative decision making are critical today.  Avoid slopes 32 degrees and steeper and give runout zones a wider berth than normal as any avalanche may exceed path boundaries.

recent observations

Observations from Relay Peak (Mt. Rose area) and throughout the forecast area showed widespread rain yesterday.  In the Relay Peak area rain was observed up to 9800' with gale force winds along ridgelines at mid day.  Blowing snow was very limited due to the rain saturated surface snow.  Cornice chucks that were intentionally dropped on test slopes did not show any signs of instabilities.  The storm began to intensify in the early afternoon hours.

Weather and CURRENT CONDITIONS
weather summary

Snow will wind down this morning throughout the forecast area with some minor lingering of snow showers and colder temperatures for today.  The atmospheric river that impacted the region yesterday into last night brought 2.5 to 6'' of rain to the Sierra Crest and over 3'' of rain to the Mt. Rose area.  Rain was observed up to over 9000' yesterday.  Snow levels slowly began to drop late afternoon through the night at the higher elevations bringing 5 to 9'' of snow to the Sierra Crest and 17'' to the Mt. Rose area.  SW winds will shift to the W today and will continue to be strong to gale force slowly decreasing into the afternoon above 8000'.  Cold and dry conditions are expected through the weekend.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 18 to 22 deg. F.
Max. temperature in the last 24 hours: 39 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 50 to 65 mph
Maximum wind gust in the last 24 hours: 109 mph
New snowfall in the last 24 hours: In the Sierra 5 to 9 inches | In the Mt. Rose area 17 inches
Total snow depth: In the Sierra 21 to 33 | In the Mt. Rose area 59 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy. Scattered snow showers. Mostly cloudy then becoming partly cloudy. Scattered snow showers in the evening. Sunny
Temperatures: 22 to 27 deg. F. 6 to 14 deg. F. 23 to 28 deg. F.
Wind Direction: W NW Light winds.
Wind Speed: 15 to 25mph with gusts to 45mph. 10 to 15mph with gusts to 30mph. Gusts up to 30mph in the morning.
Expected snowfall: Up to 1 in. Up to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy. Scattered snow showers. Mostly cloudy then becoming partly cloudy. Scattered snow showers in the evening. Sunny
Temperatures: 18 to 23 deg. F. 4 to 12 deg. F. 20 to 25 deg. F.
Wind Direction: W NW N
Wind Speed: 20 to 35mph. Gusts up to 85mph decreasing to 65mph in the afternoon. 15 to 25mph with gusts to 45mph. 15 to 25mph. Gusts to 50mph decreasing to 35mph in the afternoon.
Expected snowfall: Up to 2 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