Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

New wind slabs could have formed during the night and old wind slabs with a fragile weak layer (surface hoar) below them may still linger on isolated slopes in very wind-exposed near and above treeline terrain. The avalanche danger is MODERATE. Human triggered avalanches may be possible today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Fragile wind slabs that formed a few days ago may still linger on isolated NW-N-NE-E aspects in near and above treeline terrain. Northeast winds during the night may have been strong enough to create new small wind slabs on the NW-W-SW-S-SE aspects in the most NE wind exposed areas. Very exposed upper elevation terrain and complex terrain like couloirs, cliffy areas, and areas with multiple intersecting steep slopes represent the best places to find one of these unstable wind slabs. In some cases, these wind slabs formed on top of weak feathery snow known as surface hoar. Most avalanches resulting from these wind slabs should remain small. Small avalanches can have serious consequences especially in complex terrain or during early season with all the obstacles lurking near the snow surface. It is not impossible for a wind slab avalanche to involve enough snow to bury or injure a person (size D2) in isolated areas. 

    Signs that wind slabs may exist on a slope include cornices above a slope, wind drifts/pillows, ripples/wind-created textures on the snow surface, hollow sounding firm snow, and blowing snow. Buried surface hoar as a weak layer will make any wind slabs that do exist more difficult to manage. Surface hoar can allow remote triggering of avalanches and can allow avalanches to propagate across wider areas and run farther downslope. If there are any doubts or uncertainty about the existence of an unstable wind slab on a slope, assume the slope is unstable and avoid it. Avoiding wind-loaded terrain where problematic wind slabs may reside represents a great way to manage today's potential avalanche problem and to enjoy the cold soft snow that still remains in many more-sheltered, non-wind-exposed areas.

Avalanche Discussion

* Tests on wind-exposed slopes on Janine's Peak (Desolation Wilderness) indicated that small wind-slabs resting above weak surface hoar remain fragile. 

* Observers on Becker Peak (Echo Summit) found the 12/4 surface hoar layer buried 4 to 6 inches below the surface but did not find any signs of a slab layer above it. 

* On Maggies Peak (Emerald Bay), observations did not find any slab layers or buried surface hoar, but the upper few inches of the snowpack has become much less cohesive and some loose dry sluffing occurred in response to snowboard cuts.

* Observations from Relay Peak (Mt. Rose Backcountry) indicated that the buried surface hoar layer was decomposing in that area. Minor evidence of wind transport existed near the summit, but no wind slab formation had occurred. 

** A skier was knocked off their feet above a cliff by a small slab avalanche on Mt. Tallac on Sunday. They went over the cliff and suffered serious injuries as a result of the 200 to 300 ft. fall (some information about the rescue can be found here).

* Reasonable snow coverage exists above 7,000' to 7,500' along the Sierra Crest in most places. On the east side of the lake coverage is not as good but still adequate for careful recreation. Early season conditions still exist and even in areas with ok coverage numerous barely covered or still exposed obstacles remain.

Regions covered