THIS AVALANCHE ADVISORY EXPIRED ON January 10, 2016 @ 7:00 am
Avalanche Advisory published on January 9, 2016 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

Human triggered avalanches remain possible today due to new wind slabs and old and new persistent slabs. Persistent slabs exist on open slopes in near and below treeline terrain on W-NW-N-NE-E aspects. Wind slabs will exist on wind loaded NW-N-NE-E-SE aspects in near and above treeline terrain. MODERATE avalanche danger exists in those areas on slopes 32 degrees and steeper. Remotely triggered avalanches and avalanches that propagate long distances are possible today especially in near and below treeline terrain.

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: Persistent Slab
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Data indicates that the recent snow has consolidated and with that consolidation the lingering storm snow weaknesses have gained strength. However, the old surface hoar buried 20 to 40 cm in the snowpack on some slopes represents a persistent weak layer, and the more consolidated snow above now represents a persistent slab in areas where buried surface hoar exists. So far data has shown that this issue exists in some areas (like Andesite Ridge and possibly Red Lake Peak) but not in others. In addition to this lingering persistent slab issue, today's new snow will likely bury the widespread surface hoar that formed yesterday. This surface hoar will also serve as a persistent weak layer for another much more widespread crop of persistent slabs. These new persistent slabs will remain smaller and shallower since only 2 to 6 inches of new snow is forecasted for today, but human triggering of these of these new persistent slabs will be possible in any areas where new snow buried yesterday's surface hoar and may be likely in areas that receive the most new snow.

Triggering an avalanche from a distance, triggering an avalanche from the middle of a slope, and avalanches that propagate farther than normal are all possible with either the old larger persistent slabs or the new smaller persistent slabs. These persistent slabs will exist on any open near and below treeline slope where the old buried surface hoar exists or where newly buried surface hoar exists. It does not take much of an opening for these slabs to exist in, and they may exist in areas typically thought of as safe.

Avalanche Problem 2: Wind Slab
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New snow and wind transported old snow will combine to form new wind slabs on wind loaded near and above treeline slopes today. Human triggered wind slab avalanches will be possible. Even though only 2 to 6 inches of new snow may fall today, the leeward aspects still had soft snow on them yesterday afternoon that can also serve as material to build wind slabs. This combination of snow sources will mean that the wind slabs that form today may be larger than one would expect from only 2 to 6 inches of new snow. Avalanches resulting from the failure of these wind slabs may remain small in some areas but could involve enough snow to bury a person in other areas. In some near treeline areas wind slabs may form on top of yesterday's surface hoar and exhibit more persistent slab characteristics. The largest and most fragile wind slabs will exist on wind loaded N-NE-E aspects with smaller wind slabs on cross loaded NW and SE aspects

recent observations

Widespread surface hoar existed across the forecast area yesterday. Observations from Jakes Peak, Incline Lake Peak, Andesite Ridge, Negro Canyon, and Donner Summit all found large feathery surface hoar up to 1.5 cm in size on the snow surface. This surface hoar persisted into late yesterday afternoon on NW-N-NE-E aspects and on the upper elevation SE aspects. Below the surface snowpit tests showed another buried surface hoar layer that remains fragile on Andesite Ridge. On Jakes Peak snowpit tests did not reveal any signs of a buried weak layer. Ski cuts and snowpit tests on wind loaded test slopes on Jakes Peak and Incline Lake Peak also did not reveal any signs of instability associated with the old wind slabs

Weather and CURRENT CONDITIONS
weather summary

Snowfall started across the Sierra early this morning as as weak storm system arrived over the area. Since then 1 to 2 inches of new snow has fallen. Light snow should continue through today with another 1 to 4 inches of accumulation expected above 7000 ft. The southwest winds also started to increase last night. Since midnight they have averaged between 15 to 30 mph with gusts as high as 37 mph. These southwest winds should continue to increase and persist through today. The winds and snowfall should start to decrease tonight as the storm exits the region. By tomorrow a weak high pressure ridge should move into the area bringing clearing skies and light winds. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 18 to 27 deg. F.
Max. temperature in the last 24 hours: 26 to 33 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: Until midnight: 5 to 10 mph | Since midnight: 15 to 25 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: 1-2 inches
Total snow depth: 53 to 65 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with snow in the morning. Snow diminishing to showers in the afternoon Mostly cloudy with scattered snow showers Mostly cloudy becoming partly cloudy
Temperatures: 25 to 32 deg. F. 12 to 20 deg. F. 24 to 31 deg. F.
Wind Direction: Southwest West Variable
Wind Speed: 15 to 20 mph with gusts to 30 mph 15 to 20 mph with gusts to 30 mph in the evening decreasing overnight Light
Expected snowfall: 1 to 4 in. up to 1 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Cloudy with snow in the morning. Snow diminishing to showers in the afternoon Mostly cloudy with scattered snow showers Mostly cloudy becoming partly cloudy
Temperatures: 23 to 30 deg. F. 9 to 16 deg. F. 22 to 29 deg. F.
Wind Direction: Southwest West Southwest
Wind Speed: 25 to 35 mph with gusts to 55 mph 30 to 35 mph with gusts to 50 mph decreasing to 10 to 15 mph with gusts to 25 mph after midnight 10 to 15 mph decreasing in the afternoon
Expected snowfall: 1 to 4 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.