THIS AVALANCHE ADVISORY EXPIRED ON January 14, 2016 @ 6:59 am
Avalanche Advisory published on January 13, 2016 @ 6:59 am
Issued by Steve Reynaud - Tahoe National Forest

Considerable avalanche danger exists on NW-N-NE-E-SE aspects at all elevations due to persistent slabs and newly forming wind slabs.  On S-SW-W aspects at all elevations Moderate avalanche danger exists.  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: Persistent Slab
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Several layers of concern are present in our current snowpack that have developed over the last week.  These buried surface hoar layers exist on NW-N-NE-E-SE aspects in near treeline and below treeline terrain and should be buried anywhere from 4'' to 3' deep.  The incoming, wet and heavy storm will put additional stress and weight on these layers which could make them fail today.  There is high variability and some uncertainty as to where these layers exist throughout the forecast area.  These avalanches have the possibility to propagate large distances, be remotely triggered, and have high consequences. 

This is a near treeline and below treeline avalanche problem and is not common for our area.  Any slopes that have buried surface hoar will be suspect.  Look for recent avalanche activity, shooting cracks, and whumphing noises.  Use careful terrain selection to avoid steep open areas near and below treeline.  

Avalanche Problem 2: Wind Slab
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Dense and heavy wind slabs could form today as this winter storm affects our forecast area.  SW wind gusts are expected in excess of 100mph over the Sierra Crest.  Expect wind slabs to form on NW-N-NE-E-SE aspects near treeline and above treeline with the possibility of these winds slabs also forming below treeline in open areas.  With higher snow levels these wind slabs will be much more dense and heavy than the existing snow and could fail near the old snow/new snow interface. 

Avoid wind loaded areas.  Look for blowing snow, cornice formation, wind pillows and snow surface scouring to help identify where these wind slabs are forming.

recent observations

An avalanche was reported to have occurred in the Blackwood Canyon area in below treeline terrain.  This avalanche was snowmobile triggered, 2-3' crown line, and thought to have happened late Sunday.  The weak layer for this slab avalanche is unknow but the buried surface hoar layer is suspected in this type of terrain. 

Other recent observations across the forecast area show a well bonded and consolidated snowpack.  Yesterdays observations from Elephants Hump (Carson Pass area), West Grouse Rock (Ward Canyon area) and Little Truckee Summit (Independence Lake area) all showed no instabilities with snowpack tests and informal observations.  Surface hoar was observed throughout the day on Donner Summit and at Little Truckee Summit area.

Weather and CURRENT CONDITIONS
weather summary

A winter weather advisory remains in effect until 10pm tonight.  The forecast calls for 4 to 10'' of new snow over the Sierra Crest by this evening mainly north of Hwy. 50.  Winds will be SW at 60 to 70mph with gusts to 105mph above 8000'.  Snow levels should start out around 6500' and lower to below Lake level throughout the day.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 22 to 24 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 50 to 60 mph
Maximum wind gust in the last 24 hours: 96 mph
New snowfall in the last 24 hours: Trace to 1 inches
Total snow depth: 48 to 58 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow in the morning, then snow showers in the afternoon. Cloudy. Snow showers in the evening then isolated snow showers after midnight. Mostly cloudy then becoming cloudy. Chance of snow in the afternoon.
Temperatures: 27 to 34 deg. F. 14 to 21 deg. F. 27 to 34 deg. F.
Wind Direction: SW SW SW
Wind Speed: 35 to 45mph with gusts to 70mph decreasing to 60mph in the afternoon. 30 to 35mph with gusts to 50mph becoming west 20 to 25mph with gusts to 35mph. 25 to 35mph with gusts to 50mph.
Expected snowfall: 2 to 6 in. Up to 2 in. Less than 1 in.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow in the morning then snow showers in the afternoon. Cloudy. Snow showers in the evening then isolated of snow showers after midnight. Mostly cloudy then becoming cloudy. Slight chance of snow in the afternoon.
Temperatures: 25 to 32 deg. F. 13 to 20 deg. F. 25 to 32 deg. F.
Wind Direction: SW SW SW
Wind Speed: 60 to 70mph with gusts to 105mph decreasing to 95mph in the afternoon. 50 to 55mph with gusts to 80mph becoming west and decreasing to 35 to 40mph with gusts to 60mph. 40 to 50mph with gusts to 70mph increasing to 80mph in the afternoon.
Expected snowfall: 3 to 7 in. Up to 2 in. Less than 1 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.