Bulletin d’avalanche

Central Cascades

Central Oregon Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering avalanches will be likely in wind drifted snow and new storm snow. Triggering large avalanches on old snow weak layers is possible on west, north and east facing slopes. Avalanche danger will increase as the incoming snow stacks up; be cautious in your terrain choice and when in doubt the safe bet is to choose slopes less than 30 degrees steep. 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2.5

    Sustained winds up to the 40 mph range will be moving snow to lee terrain features. With this kind of wind speed, wind deposited snow can show up further down slope and in unusual places. It won't be hard to spot blowing snow out there. The wind wrapping around north and south aspects can cause cross loading. Wind slab avalanches have the potential to be larger compared to what we normally see during storm cycles. Look for cracking in the slab on small safe test slopes as an indicator of where this problem is present.

    Remember, wind can pile up snow many times deeper than the snow dropped by the storm. As wind slabs become deeper, avalanches can become larger.

    Although this problem will be less pronounced below treeline, blowing snow was observed in the trees on Thursday. Areas of sparse or dead trees below treeline can experience a significant wind effect. 

     

    Archive photo:

    Example of cracking in wind slab

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    The danger associated with this problem will depend a lot on how much snow falls Thursday night and Friday. I expect this problem to build through the day. Use small test slopes to check out this problem. Cracking on small convex rolls can tell you a lot about the sensitivity of the storm slabs. As the latest round of snow stacks up to 10+ inches, storm slab avalanches can start packing a punch.  Everyone likes riding deep snow, but when it doubt give the steep slopes a day or two before committing to avalanche terrain. 

    The new snow can also bring on dry loose avalanches in steep terrain. 

    Archive photo from a public observer.

    Example of a storm slab avalanche in fresh snow.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    There are multiple persistent weak layers beneath the recent storm snow. Buried facets and buried surface hoar can be found 2-5' below the surface. The new incoming snow will add stress to these layers.

    Earlier in the week, observers reported experiencing slope collapses and whumphs. However, this is a tricky problem in a sense that as the persistent weak layers become deeper we may receive less feedback in the form of whuphs and collapses. They will be less likely to trigger, but it is not out of the question. The slab on top of these weak layers is substiantial and could result in a large to very large avalanche if triggered. 

    Persistent slabs can be remotely triggered and can propagate across terrain to a larger extent compared to other slab types.

Avalanche Discussion

With multiple avalanche problems in the forecast spanning almost all the aspects and elevations, I encourage you to be cautious with your terrain choices. Natural avalanches will be possible in the new storm snow and wind drifted snow.

The wind effect will also be building cornices on some ridge features. Be cautious when approaching ridge tops. Stepping out onto a cornice can cause it to break and lead to you taking a fall down the slope below.

Régions couvertes