Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Don’t let the drop in avalanche danger lure you into a false sense of security. The consequences of a potentially enormous slide remain unchanged. Limit your exposure to any very large avalanche path including places in the forest where they may run or stop.

Problèmes avalancheux

  • Deep Persistent Slabs

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

    While cooling temperatures and a strengthening upper snowpack should help reduce the likelihood of a deep slab avalanche, the underlying weak layer remains largely unchanged. The snowpack just experienced 3 straight days of warm weather. That only increases our uncertainty about this deep layer. This avalanche problem isn’t about figuring out “if” you can trigger it. This problem revolves around recognition of the potential consequences and general avoidance. Very large and destructive avalanches occurred this week, traveled to valley bottoms, and destroyed trees. Consider significantly limiting or even completely avoiding very large avalanche paths. This includes their extreme runouts deep in the forest. 

    Many of our normal observations lack the ability to provide reliable information regarding buried deep weak layers. You may see tracks on a slope, notice an absence of cracking, and conditions could “feel” stable. None of these pieces of information should be taken as signs of stability. Even snow profiles and snowpack tests fall short when the layers sit 8-10 feet below the snow surface. Make sure you and your team discuss the potentially devastating consequences before traveling into very large avalanche terrain.

    (3/1/2021) Chair Peak produced a very large avalanche for the second time in 7 days. On Monday (3/1) debris was found to have overrun Source Lake and its berm, with an estimated crown depth over 10 feet in depth. [NE-E-SE 5800; HS-N-D3.5-R4-O; Photo: Jeff Tarshis]

Avalanche Discussion

Snoqualmie Pass may receive a few inches of snow Friday night and Saturday. This shouldn’t produce much in the way of new avalanche hazards. The snow on most slopes warmed significantly this week and as it cools, any new accumulations should bond well to the old surface. At the highest elevations, you may encounter very shallow pockets of wind drifted snow. However, we expect these slabs to remain isolated to very exposed, rocky, and confined features. Elsewhere, the new snow will overlay a thickening crust that could produce challenging travel in locations where it can not support your weight. 

While numerous layers exist in the current snowpack, the mid-January crust/facets continue to drive our avalanche forecast. A layer of weak sugary snow sits just above a very prominent crust 8-10ft below the surface. This mid-January layer produced numerous very large avalanches over the past several weeks. The most recent events occurred on 2/28-3/1 when a slide from Chair Peak descended more than 2000’, overran Source Lake, and traveled 300’ into the trees beyond. Events like this should cause us to look at all of our travel patterns with fresh eyes. Despite the lack of an avalanche problem below treeline, heightened conditions remain due to threats from above. Even as you travel in the forest, pay attention to places where your route may cross avalanche paths. Many slides ran near their historic runouts, broke trees, and traveled to valley bottoms during the past two weeks. 

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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