THIS AVALANCHE ADVISORY EXPIRED ON December 21, 2015 @ 6:56 am
Avalanche Advisory published on December 20, 2015 @ 6:56 am
Issued by Brandon Schwartz - Tahoe National Forest

MODERATE avalanche danger exists both near treeline and above treeline on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper due to ongoing wind slab development. For all other areas, LOW avalanche danger exists. Persistent slab avalanches are unlikely but not impossible in open areas below treeline and near treeline on NW-N-NE aspects.

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    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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With SW ridgetop winds in the light to moderate speed range for much of the day yesterday, significant amounts of snow on the ground remain available for wind transport. As ridgetop winds increase today, expect to see areas of blowing snow and new wind slab development in directly wind loaded and cross loaded areas near treeline and above treeline on NW-N-NE-E-SE aspects. Uses clues such as blowing snow, cornice formations, wind pillows, and cracking along ridgeline edges to determine where wind slabs exist. Unlike other avalanche problems, wind slabs are constrained by terrain and often have well defined visual boundaries, making them easier to avoid.

Avalanche Problem 2: Persistent Slab
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Persistent slab avalanches remain a lingering concern where a weak layer of collapsed surface hoar capped by thin crust exists around 12 to 24 inches deep in the snowpack. This weak layer is most often found along the Sierra Crest in open areas below treeline and near treeline on NW-N-NE aspects. Human triggered avalanches are unlikely to occur on this weak layer today. That said, in the locations where this weak layer is found, day after day snowpit tests continue to indicate that the right set of slab over weak layer ingredients are in place for avalanche activity to occur. Avoid complacency and pay attention to slope angle at all times, on the fly, both uphill and downhill. Question the placement of uphill tracks by others and set a new track if the placement is poor, exposes more than one person at a time to avalanche terrain, or has high consequences if a avalanche were to occur. Previous tracks on a slope are not a sign of intelligent life. They often just give a false sense that a poor decision was somehow okay.

recent observations

Observations made yesterday on Silver Peak (Pole Creek area) revealed small wind slabs 4 to 8 inches thick in areas of direct wind loading both near treeline and above treeline. Skier triggered cracks up to 6 feet long was observed when weighting the edge of ridgline wind pillows. The persistent weak layer of collapsed surface hoar capped by thin crust was absent in this area. Reports were received from Andesite Ridge (Donner Summit area), Rubicon Peak (West Shore Tahoe area), and from above treeline terrain on the west side of Carson Pass. On Andesite Ridge little wind affect was observed with generally good bonding reported at the old/new snow interface. On Rubicon Peak continued unstable snowpit results were reported occurring on the persistent weak layer of collapsed surface hoar and thin crust on a N aspect in near to below treeline terrain. West of Carson Pass unstable wind slabs up to 3 feet thick were reported above treeline with snowpack failure occurring within the recent storm snow.

Weather and CURRENT CONDITIONS
weather summary

Increasing winds and light snowfall are expected today as a weak weather system passes through the region. Ridgetop winds out of the SW remain moderate in speed this morning, but are expected to become strong to gale force in speed as the day progresses. Strong to gale force SW to W winds are forecast to continue through tomorrow. Maximum daytime air temperatures are forecast to reach the low 20s to low 30s today for areas above 7,000'. A warm air advection event is expected to cause snow levels to rise late tomorrow. Check in with NWS Reno for more details on that event.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 11 to 19 deg. F.
Max. temperature in the last 24 hours: 25 to 28 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 25 mph
Maximum wind gust in the last 24 hours: 45 mph
New snowfall in the last 24 hours: 6 to 12 inches
Total snow depth: 37 to 42 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Sunday Sunday Night Monday
Weather: Cloudy skies with a chance of snow. Cloudy skies with snow. Cloudy skies with snow.
Temperatures: 24 to 31 deg. F. 21 to 28 deg. F. 26 to 33 deg. F.
Wind Direction: SW SW SW
Wind Speed: 10 to 15 mph increasing to 20 to 30 mph with gusts to 50 mph in the afternoon. 20 to 30 mph with gusts to 45 mph. 20 to 25 mph with gusts to 35 mph, increasing to 30 to 35 mph with gusts to 50 mph in the afternoon.
Expected snowfall: Up to 1 in. Up to 2 in. Up to 2 in.
For 8000 ft. to 9000 ft.
Sunday Sunday Night Monday
Weather: Cloudy skies with a chance of snow. Cloudy skies with snow. Cloudy skies with snow.
Temperatures: 21 to 28 deg. F. 20 to 27 deg. F. 24 to 31 deg. F.
Wind Direction: W to SW W SW
Wind Speed: 30 to 35 mph with gusts to 55 mph, increasing to 55 to 60 mph with gusts to 90 mph in the afternoon. 40 to 50 mph with gusts to 80 mph. 45 to 50 mph with gusts to 75 mph, increasing to 65 to 70 mph with gusts to 100 mph in the afternoon.
Expected snowfall: Up to 1 in. 1 to 2 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.