Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

This storm will cause the avalanche hazard to rise significantly throughout the day. Things could become the most dangerous during periods of heavy snowfall when natural slides are more likely. Stick to lower-angled and treed terrain away from large avalanche paths as this storm plays out.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2

    The driving factor in this storm will be high snowfall rates. This could cause the avalanche danger to spike and result in a barrage of natural slides during heavy precipitation. Most of these slabs should be relatively small and only involve the new snow. However, by the afternoon, that could be 12-18in deep! In higher elevations and exposed terrain, strong winds will only make these potential avalanches larger and more difficult to manage.

    The new snow will fall on a wide variety of surfaces, including weak facets and surface hoar. Not surprisingly, some slides might trigger very easily and even remotely. Additionally, the variability will make predicting how any individual area will reach nearly impossible. 

    With all these factors at play, every steep open slope should be suspect no mater the aspect or elevation.

    (12/8/2023)

    Example: These natural storm slabs occurred during a period of heavy precipitation earlier this winter. 

    Photo: Alpental Pro Patrol

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    The presence of weak layers deeper in the snowpack doesn’t make this any easier. The additional new snow load will test this avalanche concern. However, more likely, you could see a smaller storm slab or cornice collapse serve as the “thump” a slope needs to avalanche. 

    We haven’t heard about many persistent slab avalanches at the Pass, but the structure is there. While the likelihood of these slides is lower, they could produce very deep, wide, and destructive avalanches. During a storm like this, don’t linger in the runouts of bigger avalanche paths.

    (1/10/2024)

    This very large avalanche released using explosives during avalanche control at Alpental. It is an indication that deeply buried weak layers could still be active. 

    Photo: Alpental Ski Patrol

Avalanche Discussion

This isn’t a massive storm, but it’s substantial. Given the current state of the snow surface and deeper weak layers, don’t treat this as your normal Washington storm day. 

If you’re out first thing in the morning, the hazard may not be that high. As the storm ramps up, so will the danger. Things could change quickly, and what felt very benign may suddenly seem scary. 

Observations from the past few days focus on the impacts of recent winds on the snow surface. Scoured slopes, firm wind-board, and irregular surfaces seem to be common in all but the most sheltered areas. Avalanches have been few and far between since we exited the last storm cycle. 

The new snow will create yet another interface (1/16) to track (at least in the short term). Facets, surface hoar, and weak powder (decomposing fragments) can all be found at base of the storm snow. Deeper the 1/8 and Solsitce Facet/Crust matrix still give us plenty of pause. It’s hard to say exactly how these layers will react during Wednesday’s storm, but probably best not to have a front-row seat. Put some space between you and big slide paths.

Regions covered