Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

Steer around steep terrain holding dense, wind-drifted snow. You are most likely to trigger a slab on unsupported slopes like those above or around cliffs, or on convex breakovers. Large, surprising avalanches releasing in deeper layers will be on the radar through the weekend. Very, very cold temperatures will be an additional hazard to plan for on Friday. 

Problèmes avalancheux

  • Persistent Slabs

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

    Natural, human, and explosive-triggered avalanches - all suspected of failing at the crust-facet interface buried 12/30 - have been reported from around West South starting on Saturday, Jan 6th.  Additional avalanches triggered with control work were reported today from Crystal. Noteworthy observations from many of these avalanches have been wide propagation, crowns wrapping around terrain features, and that generally light loads triggered large avalanches. 

    Calmer conditions in the coming days will open the door to the bigger, steeper, and unsupported terrain where you might find one. Use caution approaching big slopes in the coming days and get a handle on snowpack structure and recent avalanche activity before considering more complex terrain. While the likelihood will continue to decrease, the consequences remain the same. When in doubt, avoid big, steep slopes or at least choose terrain with less consequence in case you do end up triggering one of these avalanches. 

     

     

    (1/11/2024)

    The crown of a persistent slab avalanche at Crystal. It was triggered during avalanche control work. 

    Photo: Crystal Mountain Ski Patrol

  • Wind Slabs

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

    We are coming to the end of an active weather pattern and transitioning to a period of much colder, more stable weather. The widespread wind and storm slab formation observed on Thursday will end in most locations, so we will be left to deal with stubborn, day-old slabs. With an afternoon wind shift, some locations close to the crest could see another round of slab formation on south and west aspects. 

    Use the standard clues like cornices and wind-scoured surfaces to identify the loading pattern around you. Hand shears and test slopes on small, wind-drifted features can give you a sense of slab reactivity in wind loaded and also sheltered terrain. While they will be harder to trigger on Friday, you can still find a wind slab, especially on very steep unsupported slopes or around rock buttresses. Fresh slabs from easterly winds will likely be more reactive. 

    (2/1/2021)

    A shift to a more easterly wind direction Friday afternoon could reload slopes that were stripped of snow on Thursday.

    Photo: Dallas Glass

Avalanche Discussion

Stormy conditions persisted on Thursday. Observers in White Pass found extremely windy conditions along with continued snowfall. Wind effects were found well down into lower elevation terrain and touchy storm and wind slab avalanches were easily triggered on steep slopes, including a small, remotely triggered avalanche. Good riding conditions were found in areas that stayed protected from the wind. A natural wind slab avalanche was reported from Crystal at low elevations as well. In general, observations were limited given poor visibility and difficult travel conditions in many areas. 

Régions couvertes