Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Another round of heavy snow and strong winds will maintain very dangerous avalanche conditions at Snoqualmie Pass on Saturday. A weak snowpack will make managing terrain more difficult than you may be used to. Let the storm run its course by keeping away from all avalanche terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Observations from Snoqualmie Pass on Friday continue to find a weak snowpack structure within the zone which may produce larger, deeper, and surprising avalanches on Saturday. There are currently two crusts within the snowpack that have weak snow grains sitting above or below them. With continued high precipitation rates on Saturday and more load added to stress these layers, avalanches could trigger remotely or propagate widely either naturally or by human trigger. Stay away from all terrain where avalanches can start, run, or stop.

    (2/4/2021) This thin avalanche failed just above the 2/1 crust layer in the Snow Lake Divide area of Snoqualmie Pass. Similar natural and human triggered slides were reported by several professionals at Snoqualmie Pass. Photo Renne Shapiro.

  • Storm Slabs

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

    If we didn’t have an existing weak snowpack, this storm would still be capable of creating plenty of avalanches. Snowfall is expected to increase throughout the day with a slight bit of warming in the afternoon hours. These fluctuating snow levels combined with strong winds should create multiple potential weak interfaces in the recent storm snow. Any avalanche failing on these layers could act as a trigger for those deeper persistent slabs. Even if you suspect that a persistent issue does not exist in your area, you should stay out of avalanche terrain as this storm runs its course.

    (1/31/2021) This Wind Slab was intentionally triggered on a wind-loaded convexity in the Kendall area last weekend. The slab initially broke on a density change before stepping down and failing on the 1/13 crust. Similar activity is expected this weekend with much thicker slabs.

Avalanche Discussion

Saturday should be a similar storm as Thursday night at Snoqualmie Pass, except lower freezing levels are expected and the bulk of the precipitation should come during the daylight hours, increasing the hazard throughout the day. On Friday, Alpental Patrol reported slabs as deep as 3 feet triggered during control work above the rain/snow line, while wet avalanches were triggered at lower elevations. Professionals in the Kendall area were able to verify the existence of our layers of concern and weak snow grains, which are driving the Persistent Slab problem. The two layers we are most concerned with are the 2/1 crust, which has weak snow above and below it. And the Mid-January Crust (1/13), which contains weak snow above it. Although these weak snow grains have shown signs of healing in recent days, they have also been the point of failure for multiple small avalanches. 

As we continue to receive new snow and wind, slab depth atop these weak layers will increase. Slopes that have reached their tipping point already could reload and produce another round of avalanches. More concerning may be slopes that have not yet reached their tipping point.  Saturday's storm could be enough to finally tip the scales, producing large and deadly avalanches. Recent avalanches, persistent grains in the snowpack, strong winds, and heavy snow are all red flags informing you that the snowpack is unstable and needs time to heal. Continue to exercise patience and caution as this storm cycle plays out.

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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