Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 13 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger remains LOW at all elevations and on all aspects. Even though avalanches have become unlikely on a regional scale some unstable snow could still lurk on small isolated terrain features or in extreme terrain.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    A mostly strong refrozen lower snowpack with 6 to 14 inches of light, soft, unconsolidated snow as the top layer means that human triggered avalanches remain unlikely in most places today. Two potential problems have started to take shape in that light, soft snow:

    1. A buried surface hoar layer now exists in the upper few inches of the snowpack in some areas.
    2. The snow above the rain crust has started to weaken and facet.

    If and when more snow accumulates on top of the current snowpack, either of these issues could cause problems. For now keeping track of where these layers exist and how they are changing will help determine which slopes may pose future problems (see the recent observations section for more details).

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    In areas above 9,500 to 9,800 ft, rain did not percolate all the way through the old facetted snow layers on near treeline and below treeline NW-N-NE aspects. In these upper elevation areas, human triggered persistent slab avalanches are not impossible. Weak layers of well developed facets and depth hoar exist below the overlying slab of recent snow in these areas. Since there are very few areas with terrain above this elevation where these conditions exist in the forecast area this problem remains isolated in distribution.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Small wind slabs created by the light to moderate west and southwest winds moving the light, soft surface snow to leeward aspects represent another possibility for an isolated and unlikely but not impossible avalanche problem. These wind slabs could exist on a variety of aspects above treeline and along sparsely treed ridgelines. These wind slabs should remain small in size but could reach up to 1 ft. in depth in isolated areas.

Avalanche Discussion

Yesterday on Silver Peak 6 to 12 inches of soft, cold, unconsolidated snow existed above a thick, frozen rain crust. A buried layer of surface hoar remained intact within the upper part of this soft snow.

Surface hoar represents one of the weakest kinds of snow grains. While it often forms during the calm, clear, cold nights here in Tahoe, it rarely gets buried. This time Sunday's light snowfall buried this widespread layer of surface hoar under 2-4 inches of light, soft snow. Currently, it does not pose a problem because no slab layers exist above it. For now keeping track of where the surface hoar layer exists can help determine which slopes may pose future problems. While traveling in the backcountry, stop and dig into the snow from time to time. Sift the top few inches of snow through your hands. If you see any triangular shaped, striated snow grains, a shallowly buried surface hoar layer exists in that area.

Data from Silver Peak also showed that the layer of soft snow above the rain crust had started to weaken. Like the surface hoar layer it does not currently pose a problem due to the fact that no slabs exist above this soft snow.

Below the rain crust, a thick layer of refrozen snow existed in the snowpack on Silver Peak. The frozen rain crust and the refrozen layers below have become very strong and supportable. Near the bottom of the snowpack on Silver Peak, a moist layer of unconsolidated snow still existed. This layer remained weak but should gain some strength as it continues to slowly refreeze. Yesterday the strong frozen layers above it prevented all but the largest impacts on the surface from transmitting force down to those still wet and soft layers.

Regions covered