Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanches have gotten harder to trigger. However, people could still cause avalanches 4 to 6+ feet deep in some places. The impacts of such an avalanche would be deadly. Using gentler terrain away from steep slopes until this problem goes away can help avoid getting caught. 

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–4

    The weak layer buried on Dec 1 still exists near the bottom of the snowpack underneath 4 to 6+ feet of newer snow. This layer is most prominent on the NW-N-NE aspects. Getting enough force down through the newer snow to break this buried weak layer has gotten more difficult. At this point, it may take a larger trigger, like a cornice collapse, or a smaller one, like a person in the right spot. The "right spot" could be a trigger point where a shallower snowpack exists, and the weak layer is closer to the surface. If one of these avalanches occurs, it would be large and unsurvivable. 

    Weak layer depth, variability, and a lack of easy-to-see signs of instability make assessing slope stability challenging with a deep slab problem. Often triggering a catastrophic avalanche is the first and only clue that the slope is unstable. 

    Managing a deep slab avalanche problem comes down to avalanche avoidance until this problem goes away.  It takes patience and a willingness to enjoy the snow on lower-angle terrain. Recreating in sub-30 degree terrain and/or on SE-S-SW aspects where this problem does not exist represent two ways to avoid this problem and still get out in the snow.

Avalanche Discussion

  • Early yesterday and this morning, brief periods of moderate to strong NE/E winds may have produced light wind scouring, blowing snow, and small snow drifts on the highest and most wind-exposed terrain. Limited wind slab development is expected.
  • Reports of large persistent slab avalanches that failed near the storm's end (likely Sunday) keep coming in from all over the forecast area. These deep avalanches propagated across slopes and wrapped around terrain features. We have not received any reports of new human-triggered avalanches in the last two days.
  • Thanks to everyone for all the avalanche observations. Please submit an observation with a photo and location info if you see a large crown or any lingering signs of instability.

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