Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Gale-force wind, rain, and heavy snow will create very dangerous conditions today. Expect avalanches at all elevations. Traveling on, below, or near slopes steep enough to avalanche is not recommended. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    Slabs of wind-drifted snow will form on leeward aspects as gale-force winds and heavy snow impact the area. Fragile waves of overhanging snow (cornices) will also form near ridges. Large wind slab avalanches several feet deep, and cornice collapses will be very likely today. The largest and most unstable wind slabs will exist near exposed ridges, on open slopes, and in gullies on NW-N-NE-E-SE aspects in near and above treeline terrain. 

    Blowing snow and poor visibility will make accidentally stumbling onto a dangerous wind-loaded slope or close to the edge of a cornice easier. Travel in, near, or below avalanche terrain is not recommended. This includes flat areas with steeper terrain above them. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Certain
    Size
    1.5–3

    Rain on snow will create widespread areas of unstable wet snow. This wet snow will slide downhill easily. Wet loose avalanches gather more snow as they move downhill, so long, steep slopes will produce larger avalanches. Wet loose avalanches should represent most wet snow instabilities today. However, some slab avalanches that involve wet snow may also occur, especially in areas where the wet snow accumulates on top of buried surface hoar or where fluctuating snow levels create weaknesses in the storm snow. A wet slab avalanche that fails on the Dec 1 facet layer may not be impossible in some isolated spot on the eastern side of the forecast area that receives substantial rain. These issues could all produce avalanches that bury a person in soggy wet snow. Wet snow avalanches are almost certain today in areas where rain falls on snow. They could even occur above the rain/snow line in areas where soggy wet snow accumulates. 

    As mentioned above, traveling in or near slopes steep enough to avalanche is not recommended today.

Avalanche Discussion

  • Shallowly buried surface hoar existed on NW-N-NE aspects prior to this storm. Warm weather and rain likely have or will destroy it in most places, but it may linger in a few isolated areas above 8,000 ft to 10,000 ft.
  • The old Dec 1 facet layer still exists near the bottom of the snowpack on northerly aspects. Throughout most of the forecast area, this layer has gained sufficient strength to handle substantial loading. However, data has also shown that it may not handle this new loading event well in isolated locations along the eastern side of the forecast area.

Regions covered