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Out of date — this forecast expired 8 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanche danger is MODERATE for all elevations. Even though snowpack stability is improving, human triggered avalanches remain possible. Keep in mind that most recreational avalanche accidents happen during periods of MODERATE or CONSIDERABLE danger. Wind slab, deep slab, and loose wet avalanche problems may be encountered today. Areas of unstable snow will exist within greater surrounding areas of seemingly stable snow.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    A few more inches of new snow fell last night combined with moderate speed SW winds. This will have created new wind slabs near treeline and above treeline on NW-N-NE-E SE aspects. Expected avalanche size up to D2 is possible (large enough to bury or injure a person).

    Identify and avoid areas of potentially unstable wind slab. Slopes below cornice features and wind pillows are suspect today. Snow surface cracking in wind exposed areas is an additional clue of unstable snow in the immediate area.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    3

    A deep slab avalanche problem is unlikely but not impossible near treeline and below treeline on NW-N-NE aspects. The faceted (loose, sugary) weak layer of concern is buried 4+ feet deep in the snowpack in most areas. Triggering failure of this weak layer has become unlikely, but snowpit tests indicate that if collapse of this layer can be triggered, a large destructive avalanche would occur. Expected avalanche size is D3 (could bury and destroy a car, damage a truck, destroy a wood frame house, or break a few trees).

    This is a low likelihood, high consequence scenario. In steeper terrain, isolated trigger points such as single trees, exposed rocks, and convex slope rollovers should be avoided. In these locations the weak layer may be closer to the snow surface and easier to trigger. Large triggers such as multiple people on the same slope at once have a greater chance of triggering. The only way to completely avoid this problem is to stay on slopes 30 degrees or less in slope angle without steeper terrain above.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Warming this afternoon will be borderline for creating small areas of loose wet avalanche problems on lower elevation SE-S-SW aspects. This avalanche problem is expected to become more likely tomorrow. Avoid steep sun exposed slopes where roller balls are occurring.

Avalanche Discussion

* 8:15 am addition: Just in and too late for inclusion in today's advisory: Skier triggered Deep Slab avalanche on Schallenberger Ridge (Donner Summit area). More info below. Click through all of the tabs in the observation for all photos and info.

* Numerous natural wind slab and storm slab avalanches occurred during this past storm cycle. In many areas evidence of these avalanches is nearly completely covered by new snow.

* A small skier triggered wind slab avalanche occurred yesterday on Andesite Peak on a NE aspect above treeline (Donner Summit area).

* Widespread shooting cracks and whumpfing were reported on a SW aspect 34 degree slope between 7,500' to 7,825' in the Wood Creek Drainage (Mount Rose area).

* A deeply buried facet layer is the weak layer of concern for the deep slab problem. Snowpit tests targeting this layer indicate that this layer is becoming increasingly difficult to trigger but is still conducive to propagation.

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