Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

A lack of confidence in the snowpack combined with another round of stormy weather warrants a cautious approach on Friday. Avoid traveling on all open slopes greater than 35 degrees, and limit your time in the terrain below. With all the recent snow, plenty of weaknesses exists to produce large and dangerous avalanches.

Avalanche problems

  • Storm Slabs

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

    With moderate snowfall rates, strong winds, and fluctuating snow levels Thursday night into Friday, expect new and potentially easy to trigger slabs on any open slope greater than 35 degrees. Take time to make observations within the new snow. Use frequent small slope tests and hand-pits to feel the snow layers and how they might bond to the underlying surface. On southerly aspects, this new snow will accumulate over a thin crust, which could make it easier to cause avalanches in these locations. 

    This is a windy storm. Consequently, you’ll also encounter thicker and firmer wind slabs in exposed terrain at mid and upper elevations. Despite this change in avalanche problem, the travel advice remains the same; avoid traveling on open slopes greater than 35 degrees. If you suspect the wind loaded snow onto a slope, give it a wide berth. Wind slabs often catch even experienced travels off guard.

    (2/18/2021) These natural storm slab avalanches likely failed Tuesday or Wednesday (2/16-17) on Kendall Peak near Snoqualmie Pass. SW 5400. SS-N-D1.5/R2-N.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    On Thursday NWAC staff investigated the deep persistent weak layers at one location at Snoqualmie Pass. Weak facets above the mid-January crust showed little sign of change over the past week. Snowpack tests continued to produce sudden results suggesting avalanches may still occur. Our last observed slide on this layer occurred Feb 10, however stormy weather limited recent observations. You may see avalanches step down into this old snow or you could trigger slides from shallower points in the snowpack. Any resulting avalanche would certainly become very large and destructive. Consider staying out of large open startzones and limiting your exposure to the terrain below them.

    (2/18/2021) This snow profile shows the upper 7+ ft of the snowpack. You can see all three prominent persistent layers mentioned in the forecast.

Avalanche Discussion

The active weather pattern continues. Snoqualmie Pass went 30 hrs without recording precipitation Wednesday into Thursday. Now another storm system may drop nearly a foot of snow by Friday afternoon. This will maintain and even slightly increase the avalanche hazard. Expect the most dangerous avalanche conditions in the morning and during periods of heavier snowfall. Recent storms deposited more than 4’ of snow at the Pass between 2/11 and 2/16. This resulted in nearly a week straight of natural and triggered avalanches up to 3’ thick. Many of the weaknesses within the storm snow show significant signs of gaining strength. However, avalanches could continue to fail or step down into these recent storm layers in isolated areas. Deeper in the snowpack still, you can find the 2/1 and mid-January persistent weak layers about 6ft or more below the surface as of Thursday. Weak facets above both of these crusts continue to give us pause. Due to the depth of these layers monitoring and tracking continues to be very difficult. A high degree of uncertainty exists surrounding the potential for these persistent weak layers to produce avalanches. 

With all the recent snow, expect deep travel conditions. This brings with it the risk for deep snow immersion and tree well hazards. Please follow this link for more information. 

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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