THIS AVALANCHE ADVISORY EXPIRED ON January 29, 2017 @ 6:59 am
Avalanche Advisory published on January 28, 2017 @ 6:59 am
Issued by Andy Anderson - Tahoe National Forest

Human triggered wind slab avalanches may remain possible today due to wind slabs lingering in near and above treeline terrain. MODERATE avalanche danger exists on near and above treeline slopes. LOW avalanche danger exists in below treeline areas. Evaluate snow and terrain carefully before committing to a route. Use this information to identify features of concern like wind slabs and plan a route to avoid those areas of concern.

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Some wind slabs exist on near and above treeline slopes loaded by the east winds steeper than 35 degrees. These stiff wind slabs would be difficult to trigger, but it may still be possible for a skier to trigger one of these wind slabs today especially in complex or extreme terrain. Larger triggers like multiple people on a slope or large cornice collapses would have better chances of triggering one of these wind slabs. The largest of these wind slabs will exist on directly wind loaded NW-W-SW aspects, but they could also linger on some cross loaded N and S aspects as well.

Blowing snow, cornices, wind scoured surfaces, ripples, and other wind created textures can help identify where wind slabs may exist. The hard wind slabs that exist on some aspects may also sound hollow due to the soft snow underneath them. 

recent observations

Yesterday observations in the Donner Summit area showed firm wind slabs formed by the east winds on NW-W-SW aspects near ridgelines. Ski kicks on some test slopes where these wind slabs existed triggered some cracking and collapsing. Some of the wind loaded test slopes required several kicks or two people kicking the slope to trigger cracks in the firm and stubborn wind slabs. On Andesite Peak some natural cracking that looked to have occurred early yesterday morning also existed. Snowpit observations showed a firm, dense wind slab up to 18 inches thick resting on top of light, soft snow. Tests showed that if the wind slab did break the fracture could travel along the interface between the dense wind slab and the soft cold snow below it. East winds continued to transport snow throughout the day in this area. Across the Lake on Tamarack Peak, smaller wind slabs that did not extend very far away from ridgelines existed and cracking in these slabs was much more isolated and did not propagate very far. South of the Lake on Monument Peak, observers also reported less wind slab formation. In all of these areas: Donner Summit, Tamarack Peak, and Monument Peak, wind scoured surfaces existed on exposed near and above treeline N-NE-E-SE aspects with softer snow on the sheltered below treeline slopes. Sun crusts and sun affected snow started to exist on sun exposed slopes. 

Weather and CURRENT CONDITIONS
weather summary

East winds started to decrease over the Sierra Crest during the night and should continue to diminish today with the forecast calling for light winds at the lower elevations and ridgetop winds in the 10 to 15 mph range with some stronger gusts. After midnight tonight, the forecast calls for light winds at all elevations. The high pressure over the region should allow warmer daytime highs and sunny skies to prevail through Monday. The calm clear weather will also allow cold air to get trapped in the valleys creating inversion conditions. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 21 to 32 deg. F.
Max. temperature in the last 24 hours: 27 to 36 deg. F.
Average wind direction during the last 24 hours: East
Average wind speed during the last 24 hours: 35 mph
Maximum wind gust in the last 24 hours: 59 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 107 to 133 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Partly Cloudy Clear Sunny
Temperatures: 36 to 41 deg. F. 14 to 24 deg. F. 41 to 46 deg. F.
Wind Direction: Variable Variable Variable
Wind Speed: Light Light Light
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Partly Cloudy Clear Sunny
Temperatures: 37 to 42 deg. F. 22 to 28 deg. F. 41 to 46 deg. F.
Wind Direction: East Variable Variable
Wind Speed: 10 to 15 mph with gusts to 40 mph in the morning becoming light in the afternoon Light Light with gusts to 25 mph in the morning
Expected snowfall: 0 in. 0 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