Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

HIGH avalanche danger exists for all elevations and aspects due to a combination of wind slab, storm slab, and deep slab avalanche problems. Travel in avalanche terrain, on or below slopes 30 degrees and steeper is not recommended. Avalanches could run into areas of mature forest. A backcountry avalanche warning is in effect through at least 7 am Wednesday.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    3

    Feet of new snow combined with gale force SW winds has and will continue to create very large wind slabs in near treeline and above treeline terrain mainly on NW-N-NE-E-SE-S aspects. Wind slabs may form in more isolated areas below treeline and on SW-W aspects today.

    Travel on or below slopes steeper than 30 degrees is not recommended today. Very large cornices are expected to form along ridgelines, presenting an additional hazard.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Rapid new snow accumulation in wind protected areas near and below treeline has and will continue to create storm slabs on all aspects. Rising snow level could further contribute to storm slab formation with a potential for upside down storm snow structure. Any areas where rain on snow occurs today will allow these same storm slab areas to experience wet slab or wet loose avalanche problems.

    Travel on or below slopes 30 degrees and steeper is not recommended. Trees will need to be too tight to move through on skis or a snowmobile to protect from direct human triggering of this avalanche problem. Keep in mind that avalanches from above can move through mature forest.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3

    By current definition, deep slab avalanches are anything that fails more than 3 feet deep in the snowpack regardless of weak layer type. Several possibilities exist for deep slab avalanches to occur today. Drifting snow associated with wind slabs will easily become large enough today to qualify as deep slabs. A new rain crust buried Jan 9 will provide an efficient bed surface and potential new weak layer at the base of the current storm snow. Failure much deeper in the snowpack down to the depth of the Dec 15 rain crust remains possible, especially above 9,000'. Deep slabs could form on any aspect at any elevation.

    Human involvement in any deep slab avalanches will be difficult to survive given the expected very large to historic avalanche size. Travel on or below slopes 30 degrees and steeper is not recommended. Avoid historic avalanche run out zones characterized by small to medium sized trees with steeper slopes above.

Avalanche Discussion

Observations were made and received yesterday from Hidden Peak (West Shore Tahoe area) and in Negro Canyon (Donner Summit area). On Hidden Peak at 8,250' rain wetted non-refrozen snow existed in the top 4 feet of the snowpack with signs of significantly increased moisture down to the level of the Dec 15 rain crust located 6 feet deep in the snowpack at that particular wind protected location. In Negro Canyon, strong snow temperature gradients were measured at the newly formed and buried Jan 9 rain crust. This indicates a potential for a new weak layer of near crust facets to form on top of the Jan 9 rain crust at the base of the most recent storm snow. No new avalanche activity was reported to have occurred during the day yesterday.

Regions covered