Bulletin d’avalanche

Central Cascades

Central Oregon Avalanche Center
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Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering an avalanche will be possible on North and East slopes that the wind has blown new snow onto.  Near treeline, these avalanches could be large enough to bury or injure a rider.  Above 8,000 ft. these Wind Slab avalanches could "step down" to older weak layers in the snowpack and the resulting avalanche would be very large.  My decision-making on North and East slopes above 8000 ft. has been a bit more conservative than it otherwise would be because of this potential for very large avalanches.

Problèmes avalancheux

  • Loose Dry

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

    The wind ramped up in the alpine on Monday afternoon.  I observed Moderate and Strong winds on Ball Butte, and surely high in the peaks the wind was Intense.  This means that we can expect both predictable loading patterns (immediately below ridgelines and behind features), but also variable loading up high where snow was transported further down wind.

    On Monday, the Wind Slabs that I observed were about 30 cm. thick and sometimes consisted of multiple wind slabs formed over each other.  With more snow in the forecast Wind Slabs could be large.  Relatively high snow levels early Monday night mean that areas above 7700 ft. will get more snow.

    Last Thursday Mt Bachelor Patrol triggered a Wind Slab that stepped down and produced a very large avalanche.  I'm keeping this event in mind when choosing terrain above 8,000 ft. and avoiding big steep slopes on North and East aspects.

  • Deep Persistent Slabs

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

    Mt Bachelor patrol triggered a Deep Slab on last Thursday with explosives.  Triggering a deep slab is unlikely at this time in the backcountry.  Triggering these deeper layers would require a lot of force.  In the backcountry this means first triggering a Wind Slab which could step down to the deeper layers or in the event of a Cornice Failure.  Be cautious on large steep slopes above 8,000 ft. that may be wind loaded.

    Observers and forecasters have been doing a lot of digging to look at these weak layers (particularly weak snow beneath the 12/7 crust and 11/22 crust).  We've been finding the 12/7 crust down 90-140 cm. depending on elevation.  Most recently I haven't been finding much for weak snow under this crust and haven't been seeing test results indicative of avalanches.  Nonetheless, a very large avalanche 4-days ago is too recent to forget.

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