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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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The likelihood of triggering an avalanche has gradually decreased but the consequences have not. Isolated areas of unstable snow linger due to a persistent slab avalanche problem. Any isolated avalanches today are likely to be larger than expected. MODERATE avalanche danger lingers at all elevations. Increasing avalanche danger is expected tomorrow.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The likelihood of triggering an avalanche has trended downwards over the last few days. Signs of instability in the deeper old snow layers are becoming increasingly isolated. The most recent signs of obvious persistent slab instability were reported on January 1. Unfortunately, the consequences of triggering an avalanche remain elevated with the potential for wide propagation and larger than expected avalanches. Mid slope avalanches and avalanches occurring on slopes with numerous tracks are also a possibility. Concern for this avalanche problem exists at all elevations on W-NW-N-NE-E aspects.

    The easy way to deal with this avalanche problem is to choose to travel only on sub 30 degree angle slopes without steeper slopes above or to the side. Otherwise, moving into steeper terrain should utilize cautious, skilled, unrushed snowpack assessment. Avoid writing off any clues to instability in the deeper old snow layers regardless of isolated occurrence.

     Photo: Signs of persistent slab instability on January 1 near Brockway Summit, CA.

Avalanche Discussion

* An unforecast mist/light rain event affected most of the forecast area yesterday. Some minor roller ball activity was reported. A thin new crust is likely to have formed on the snow surface last night in areas below 8,000' and possibly up to 9,000' in some locations.

* Newly formed wind slabs were dense and difficult to trigger yesterday.

* The Dec 11 PWL continues to gain strength but an overall poor snowpack structure remains. The most recent signs of instability on this layer were reported from near Brockway Summit on January 1 with snowpack collapsing, whumpfing, test slope failure, and unstable snowpit test results.

* Surface hoar buried within the top few inches of the snowpack has been reported from some locations.

Regions covered