Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dry snow avalanche concerns exist at upper elevations as a cooling trend and overnight snow reminds us that winter isn't quite done yet. Pay attention to thicker drifts of dry new snow and steer around these areas on steep slopes. Lingering concerns for very large avalanches on upper elevation, large, northerly slopes still exist. 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    A couple inches of snow overnight and during the day Thursday, on top of the few inches that fell Wednesday, slightly elevates concern for wind slab avalanches on upper elevation slopes. Light to moderate winds could shift the snow into thicker slabs, and possibly make them reactive to a human trigger. Search for thicker drifts on leeward ridgelines, around rocky outcroppings, and in gullies. Avalanches in these drifts probably wouldn't be large enough to bury you if you triggered one, but if you're near a terrain trap they could still cause harm. Pay attention to signs of weakness like cracking. Also make note of the new snow in regards to the layers beneath it. These drifts will probably be less than a foot deep, so you could dig down and see whether the snow is sticking well to the underlying layer, or if it easily slides on the old snow surface. Snow that easily slides as a cohesive slab will be more likely to avalanche. If you find these conditions, steer around slopes greater than 35 degrees.

    (3/20/2022)

    Small wind slab avalanches could occur at upper elevations on leeward slopes and around rocky outcroppings. 

    Photo: Ryan Minton

  • Deep Persistent Slabs

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

    A layer of faceted snow 4-8 feet deep is likely behind very large avalanches that occurred in the past two weeks. Though you're more likely to encounter a shallow avalanche Thursday, the rare deep slab avalanche will be much more dangerous if you happen to be in the way.  It’s quite unlikely a single person could trigger one of these avalanches but they could still be provoked by a big load like cornice fall, slab, or loose snow avalanche from above. Overall the danger from these is diminishing as colder temperatures make for less cornice fall and other natural activity. That being said it’s still a good idea to not linger on big, northerly alpine slopes below cornices or other hazards.

    (3/27/2022)

    A very large (D3) deep slab avalanche below Hidden Lake Lookout in North Cascades National Park, just barely in the West North zone and very close to the West Central zone. It was likely triggered by a chunk of cornice falling from above. Northeast aspect at 6700'.

    Photo: John Scurlock

Avalanche Discussion

Dynamic springtime conditions are reminding us winter isn't done yet. Low-density dry powder may land on moist snow layers.  While the day will remain mostly cloudy and it'll feel like winter up high, we might see wet loose avalanches at lower elevation or maybe in the mid-elevation band where a little bit of low-density snow fell overnight and during the day. Despite gaining strength from our recent cooling, the overall warmer trend means cornices aren't as strong as they once were. Pay attention to overhead hazards if you're traveling in large terrain, especially in areas where the persistent deep slab remains a concern.  

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