Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
4 · High
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Out of date — this forecast expired 6 years ago.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

The snowpack does not like rapid change and this dynamic storm continues to change conditions dramatically. Very large and destructive avalanches may run from upper elevations down to valley bottoms. Travel in or below terrain where avalanches can run or stop is not recommended.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    Additional snowfall and strong winds will continue to overload the snowpack and produce natural avalanches on Tuesday. Slabs will increase in size and reactivity as you ascend in elevation above the previous rain/snow line or where strong winds are able to thicken slabs or create complimentary Wind Slabs. We expect most avalanches to entrain significant snow, with the ability to run far distances and possibly step down to older layers in the snowpack. Even with lower hazard forecasted below treeline, slides are expected to run down into this elevation band. Many common low elevation travel routes may be in danger of overhead hazard. Tuesday will be another day to stay far away from large avalanche paths or slopes over 35 degrees.

    (2/22/2021) This very large avalanche (D3.5) started high on Denny Peak and ran full path (2500 vertical feet), under I-90, and then down into Franklin Falls where avalanche debris filled the pool. [Photo: John Stimberis/WSDOT Avalanche Crew]

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Significant loading will continue to test the deeper weak layers in our snowpack on Tuesday. We don’t know of any recent avalanches on these layers in the zone, but the setup is still there and they have started to awaken in the neighboring Stevens Pass and the East Central zones. The Mid-January crust was last measured close to 7 feet down and the 2/11 layer closer to 4 feet down from the surface before this atmospheric river event began. There could be slides on these layers from Monday, but we just don’t know about them yet. If the added load from this storm is enough to activate these layers, very large and destructive avalanches will occur. These slabs could release naturally or be triggered by other avalanches stepping down to the Mid-January crust. Continue to give all large avalanche paths and open slopes a wide berth until this storm is over.

    (2/20/2021) This deep avalanche likely failed on the mid-Jan crust Saturday near Stevens Pass. S, 4900' Photo: Wash DOT NCR.

  • Glide Cracks

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

    We just received a lot of rain at lower elevations, resulting in a significant wet avalanche cycle and we may not be done yet. It can take some time for water to percolate through the snowpack and weaken the bonds between snow crystals, releasing natural avalanches. Although listed as Glide, other wet snow related avalanches such as Wet Slab and Wet Loose are still on our minds, as these problems are often intermingled. The general cooling trend should help to minimize wet avalanche activity, but the reality is that the snowpack needs time to adjust to all the recent rain. Since wet avalanches are not well understood and the timing of wet avalanches are very difficult to predict, they can act in surprising ways. You can mitigate this uncertainty by minimizing your exposure through the selection of safe travel routes, staying off slopes over 35 degrees, and being aware of terrain above you at all times, especially if you notice large cracks in the snow that look like crevasses. 

    (2/22/2021) This very large (approaching D3) wet avalanche released naturally overnight on Sunday, running almost full path. It ran close to 1400 vertical feet on a SE aspect. [Photo: John Stimberis/WSDOT Avalanche Crew]

Avalanche Discussion

The pass has received over 3.5” of water since Sunday afternoon and it is going to keep snowing. Much of that precipitation fell as rain at lower elevations but should switch to snow as we move into Tuesday. Don't be surprised to find over 3 feet of new snow above the atmospheric river's rain/snow line. We have a lot of uncertainty around conditions in the mountains right now, but we do know that we just received a lot of water in a short period of time, and that avalanches did occur. Observations on Monday were obviously limited, but we got word of a few very large slides reported by avalanche professionals at WSDOT. Slides as large as D3.5 were reported, which ran both naturally on Sunday night and through avalanche control measures by the WSDOT avalanche crew. 

On Tuesday, you may not see a widespread natural avalanche cycle initiated at lower elevations since the wind will not be able to effectively help load the snowpack, but that doesn’t mean that it is safe. You will still be able to trigger avalanches as you travel and very large avalanches could come down from upper elevations into areas many people often consider as safe zones. One of the slides reported by WSDOT started high on Denny Peak and was able to run and fill up the pool at Franklin Falls, which is a common snowshoe/hiking destination down “in the flats”. With so much recent snow, any avalanche could step down or entrain enough snow to grow very large and destructive. Near ridgelines, cornices may have been freshly built by wind and new snow or destabilized by the rain, and could be primed to act as triggers on the slopes below. Continue to practice patience by letting this storm wrap up and allowing the snowpack to adjust to all of the recent changes.

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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