Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 4 years ago.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

Highlights

Sunday may not be your usual post-storm day in the Pacific Northwest. Instead of the snow stabilizing, it could become more reactive. Add in some uncertainty about a buried weak layer, and you have a recipe for some unusual avalanches. When in doubt, give the snowpack time to adjust to the recent load by avoiding slopes over 35 degrees.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    If you were out in the mountains on Saturday, you may have found the recent snowfall to be generally light and fluffy. Snow that failed during uptrack tests, hand shears, or in your pits likely fell to pieces. While most slabs identified were indeed soft, that doesn’t mean that they’ll remain that way going forward. Fluctuating temperatures could help the snow to “slab up” more on Sunday or become more cohesive. Look for heavy snow over weaker snow, blocks failing in your tests, or cracking of the snow surface to help you understand how the snow is behaving. If you notice these signs, you should avoid open steep slopes over 35 degrees.

    To complicate matters, buried surface hoar was identified in the zone on Saturday (more in the discussion). If slabs are breaking on these persistent grain types, they can act in surprising ways such as propagating far distances or wrapping around terrain features. If you dig and see a thin gray line in the snow around the depth you are getting failures in your tests, you’ve likely found the issue and should take extra care.

    (12/9/2022)

    This skier triggered avalanche occurred Friday 12/9 in the Alpental Valley. N-NE, ~4000ft. SS-AS-D1-R1-U

Avalanche Discussion

A common phrase heard around Snoqualmie Pass on Saturday was, “there is way more snow than I was anticipating”. With well over a foot falling on Friday night, the storm total since 12/8 is approximately 2 feet. We may still squeak out another inch or two before this storm is finished on Sunday. 

On Saturday, NWAC forecasters in the Alpental Valley were able to confirm buried surface hoar does exist in the zone. Where it is present, you can expect to find this layer (12/8) anywhere from 1.5-2 feet below the surface and you may see a thin gray line. We are still getting a handle on its distribution, but if adjacent zones are any indication, it could be fairly widespread. It has been identified in the Mt. Hood, Olympics, West South, and Stevens Pass zones. We do not currently have any confirmed avalanches on this layer at Snoqualmie Pass. However, on Friday, three skier-triggered avalanches in the Alpental Valley appear to have broken at a depth that matches the 12/8 well. In the neighboring West South zone, there was a skier-triggered avalanche at White Pass that is believed to have failed on the 12/8 surface hoar. The avalanche was a hard slab close to 2.5 feet deep at its thickest and 150 feet wide. Avalanches such as this are not out of the question at Snoqualmie Pass on Sunday, particularly at mid to upper elevations. You should ease into terrain carefully and research what lurks beneath. 

With so much recent snow, early-season hazards are diminishing, but you should still look for holes and open creeks. And keep your partner in sight, it could be a struggle to get up if they stumble. 

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