Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Sat
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

The presence of a persistent weak layer lingering in our snowpack continues to maintain avalanche danger around the Pass. While it may be unlikely that you’ll trigger one of these slides, if you do, it could result in a large avalanche. Consider managing this uncertainty by simply avoiding steep open slopes.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1.5–2.5

    A layer of buried surface hoar and large preserved stellars (snowflakes) continue to persist in the upper snowpack around the Pass. While we haven’t heard of any avalanches on this layer this week, professionals continue to find it fails suddenly in snowpack tests. This indicates it could produce an avalanche in the right spot. Unfortunately, all steep open slopes should be suspect. So, how do we manage this uncertainty? Dial back your terrain choices and seek out small, lower-consequence areas, and consider avoiding all large steep open slopes. 

    If you dig, you’ll likely find a layer of buried surface hoar about a foot (25-35cm) below the surface. Since this layer is starting to heal, it may not immediately pop out to you. Snowpack tests often quickly highlight this interface.  While snow profiles can help locate this persistent weak layer,  they can’t prove its absence.

Avalanche Discussion

It feels like we’re stuck in a rut this week. Moderate danger and soft snow typically mean lots of fun winter travel. However, not all moderate danger is the same. The presence of a possible persistent slab in the zone should cause us all to carefully reconsider our terrain choices. While we continue to gain confidence that this layer is starting to heal, reports from avalanche professionals Wednesday showed it could still produce slides. This isn’t the time to let our desires for this problem to go away to get ahead of what observations demonstrate. At lower elevations, warmer temperatures and heavy wet snow seem to have destroyed this concern. 

Avalanches: We’ve only seen 4 slides we suspect failed on this weak layer at the Pass. 

12/9: Three small skier-triggered slabs in the Alpental Valley likely failed on surface hoar. An NWAC forecaster found this weak layer in the vicinity the next day. 

12/11: A small natural avalanche was observed on Mt Catherine, that likely failed the day prior. 

Periodic sunshine this week formed a thin crust on steep southerly slopes. While this may soften and produce a few rollerballs Friday, it shouldn’t pose any real hazard. In shaded areas, soft dry snow remains at mid and upper elevations. 

Friday will be the last clear day prior to a more active weather pattern. A new crop of surface hoar and facets formed this week. With snow in the forecast, today’s surface could become tomorrow’s weak layer. If you’re out, take a photo of the snow surface and let us know what you find, before these grains are hidden from view.

Régions couvertes