Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Thu
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 possibility of triggering a low-likelihood, high-consequence avalanche should be shaping your travel plans at Snoqualmie Pass on Wednesday. You could be out in the mountains all day and not see any signs of instability. Don’t let that lull you into a false sense of security. If you find the sweet spot to trigger a slide, it will likely be large enough to bury or kill you.

Problèmes avalancheux

  • Persistent Slabs

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

    Persistent Slab problems are tricky. Tricky to manage, tricky to forecast, and tricky to put to bed. They can fail in surprising ways by spanning far distances, breaking above you, or wrapping around and connecting terrain features. You should be traveling cautiously in terrain and doing your homework before committing yourself to a slope. Think about traveling as if conditions are Considerable, not Moderate, even though the likelihood of triggering one of these slides isn’t very high. In fact, you could be out all day and not see a single sign of instability. You may have to dig in order to find out what potential issues lurk beneath the surface.  

Avalanche Discussion

NWAC forecasters and avalanche professionals were out putting holes in the ground again on Tuesday, taking a look at the 12/8 interface. It was generally found about a foot below the surface and continued to produce failures. On Wednesday, we’ll be 4 days out since our last major loading event, and the fact that this layer is still showing up in snowpack tests should give you all the information you need to know. It is not healing as quickly as we are used to seeing with a standard Cascade storm interface.

While the likelihood of you triggering an avalanche on this layer is low, there is enough uncertainty that we cannot call conditions generally safe at this time. If you do trigger one, the slide will likely be large enough to bury or kill you. While the BTL is not out of the question for this avalanche problem, we do feel that there is even less of a chance of you running into an issue. 

One reason we suspect there is less of an issue BTL is that the snow was wetted at the tail end of the storm and has gotten quite heavy. There are also more shrubs, creeks, and other natural hazards poking out of the snow to help anchor the snowpack (and for you to avoid). As you ascend in elevation, the snow gets progressively drier. On slopes that see direct sunshine, a thin crust has been found on the surface, somewhat of a rarity this time of year. Although the wind was a little gustier and chillier than expected on Tuesday, it didn’t appear strong enough to form new Wind Slabs. All the same, if you’re going to venture into high elevation or extreme terrain, keep an eye out for areas that look “fat” or have rippled surfaces near rocky gullies or cliffs. 

Régions couvertes