Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

MODERATE avalanche danger exists at all elevations due to new and old wind slabs and a possible lingering deep slab problem. Human triggered avalanches remain possible today. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Human triggered wind slab avalanches could be possible on any wind exposed slopes on any aspect today. Strong NE winds over the last 24 hours combined with snow available for transport may have allowed new wind slabs to form on typically windward W-SW-S aspects. Older wind slabs formed by SW winds during the storm could also still exist in some places on N-NE-E aspects. Both wind directions could have cross-loaded the NW and SE aspects. Wind slab avalanches could involve enough snow to bury a person or injure a person or could be even larger in the most heavily wind-loaded areas.  

    Identify terrain where wind slabs may exist using clues like cornices above a slope, blowing snow, hollow sounding firm snow, and other wind created features. Not only will these areas be more likely to hold wind slabs but they may also hold less fun snow conditions. Choosing slopes sheltered from the wind could provide better snow conditions and fewer avalanche concerns. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    While deep slab avalanches have become difficult to trigger in most places, they may remain possible on some NW-N-NE (and maybe E) facing slopes. Large triggers like falling cornices, other avalanches, or multiple people on the same slope may still be able to trigger a deep slab in some terrain. Complex terrain with steep cliffy areas, overlapping avalanche paths, and lots of trigger points represents the most suspect terrain. Significant uncertainty exists concerning whether or not deep slab avalanches could occur. 

    Unfortunately, these are hard to predict and careful snowpack evaluation may miss the problem. Due to the uncertainty surrounding this problem and its potential consequences, creating travel plans with larger than normal safety buffers represents a good choice. Identifying and avoiding terrain where deep slabs may exist remains one of the only ways to effectively deal with deep slab problems even on a MODERATE day.

Avalanche Discussion

* A skier triggered avalanche occurred in the Sand Chutes on Mt. Rose. It ran several hundred feet down the chute. This slide was reported by a party who saw it from a distance and no other details were available. 

* Observations from the Powderhouse Peak, Hidden Peak, Rubicon Peak, and Tamarack Peak all found that ski kicks on small wind-loaded test slopes near ridges would produce small shooting cracks in the wind slabs. A party on Jakes Peak also reported some "wind slab activity" but did not give any other details. NE winds were transporting snow for much of the day on Tamarack Peak.

* Snowpit data from Hidden Peak targetting the deeply buried surface hoar and old facet layers indicated that these old persistent weak layers may have gained some strength in that area.

* The Kirkwood Ski Patrol was able to remotely trigger a deep slab avalanche on a difficult-to-access, rarely-skied slope with a 2lb explosive shot placed 100 ft away from the slope. This slide broke on the old facet layer that is now more than 4 ft. deep. While this did release in a ski area with explosives, it may be representative of what could happen in the backcountry with larger triggers. 

Regions covered