Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

A strong winter storm with heavy snow and gale-force winds will create dangerous avalanche conditions. Large avalanches could start on any steep slope at any elevation. They could run down into treed areas below. Avoid traveling on, below, or near slopes steep enough to avalanche.

Avalanche problems

  • Wind Slabs

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

    Gale-force winds and feet of new snow will build large slabs of wind-drifted snow and fragile cornices on the downwind sides of ridges, open slopes, and exposed gullies. The largest and most unstable wind slabs will form on NW-N-NE-E-SE aspects in near and above treeline terrain. Large wind slab avalanches that fail under the weight of the new snow or a cornice failure (natural triggers) will likely occur. People could also trigger wind slab avalanches easily if they venture onto/near a wind-loaded slope. These could also cause the Dec 1 persistent weak layer to fail as they move downhill. This would result in much larger and deeper avalanches that could travel into below-treeline terrain and could break across terrain features. 

    Blowing snow and poor visibility today make accidentally stumbling onto a dangerous wind-loaded slope or close to the edge of a cornice easier. Today is a day to avoid all avalanche terrain.

  • Persistent Slabs

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

    Even though it has been days since the last persistent slab avalanche, the Dec1 facet layer could easily re-awaken as the load on top of it doubles during this storm. Large triggers like 2-4 feet of new snow, falling cornices, or other avalanches will likely cause persistent slab avalanches. A person could also trigger one of these avalanches as the weak layer gets loaded today. These avalanches break wider than expected, wrap around terrain features, and travel farther downhill than usual. They can be triggered remotely from nearby slopes or flat areas at the bottom of a slope. The most widespread and weakest snow existed on NW-N-NE aspects, but this load may be enough to break less weak snow on other aspects as well. 

    Very dangerous avalanche conditions will exist today. The best plan is to avoid traveling in or near avalanche terrain. Poor visibility/driving snow will make seeing the terrain around you and identifying avalanche terrain even harder today. 

    (12/7/2022)

    One of two wide propagating natural avalanches on this slope. Likely occurred on Dec 3 or 4. N aspect terrain around 7,700'. Deer Creek drainage near Mt. Watson, CA.

  • Storm Slabs

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

    Unstable slabs of storm snow will form during this storm due to the intense snowfall rates and rapid snow loading. These storm slabs could exist on any steep slopes in wind-protected areas near and below treeline. Some may even form on top of buried surface hoar making them easier to trigger. If the tree spacing allows easy travel and slopes are steep enough to avalanche, then they can produce storm slab avalanches. Again, avoiding avalanche terrain is the best plan during this storm. 

Avalanche Discussion

  • The Dec 1 facet layer has become more variable over the last several days, with some observations indicating it remains unstable and others indicating that is it more difficult to trigger.

Regions covered