Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sat
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You can trigger large and dangerous wind slab avalanches possibly up to several feet deep. Strong winds developed reactive slabs which you may find further downslope than you might expect. Stay off slopes greater than 35 degrees, and avoid runouts beneath avalanche paths as well.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2

    Very dangerous wind slab avalanches are your biggest concern on Friday. At least two feet of snow fell in the last 36 hours, and winds were strong, redistributing the fresh snow into touchy slabs. In some areas, these could fail naturally- especially in gullies, beneath rock bands, below cornices (which are getting very large) and under ridgelines. Your added weight makes an avalanche occurring on steep slopes very likely.  

    The strong wind stripped some areas back to firm surfaces, while other slopes and features have thick pillows of snow up to several feet deep. You may find slabs in unusual locations, such as lower on a slope than you would normally suspect. There are a number of underlying layers of concern which avalanches could fail on, such as a sun crust from Wednesday’s intense sun on steep southerly slopes, or a layer of graupel in other areas. You may find slabs 6 inches to several feet thick. Due to this uncertainty stick to slopes less than 35 degrees on Friday, and avoid lower angle terrain which is beneath avalanche paths as well. 

    A small natural wind slab avalanche. Note the cornice above the feature that failed- this was an obviously wind loaded slope.

  • Loose Dry

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

    Loose dry avalanches can occur naturally or with a human trigger in areas that are sheltered from the wind. On Thursday there were reports of loose avalanches on steep wind sheltered slopes, treed or not, at lower elevations. As temperatures remain cool and winds back off a little, expect conditions to remain similar on Friday. Stay alert, as they may run naturally as well. Check on the depth of the low density snow at the surface to make estimates on how deep the avalanches may get, and avoid travelling in areas where terrain traps such as cliffs, trees or gullies are present if you think you may encounter one of these avalanches.

    (1/29/2021) Small dry point releases in steep terrain on Mt. Herman. Photo: Simon Trautman

Avalanche Discussion

Earlier this week a large storm and extensive avalanche cycle ran its course throughout the Cascades. Very large natural avalanches occurred in the West North zone, the most impressive of which were natural avalanches that ran 4000 vertical feet, hitting Highway 20 in Newhalem on Sunday night. After an epic bluebird powder day on Wednesday we’ve jumped right back into another storm. The short break helped stabilize new snow instabilities, but weaknesses are still a concern in the top several feet of snow. This is especially the case with all our recent snow that redistributed in the last 36 hours with wind. Keep alert so you don’t get caught in any avalanches at the tail end of this storm.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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