Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Thu
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Out of date — this forecast expired 6 years ago.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

Avalanches on Wednesday will be easier to trigger on steep slopes, convexities, or wind-loaded features. There is a lot of uncertainty around conditions, so keep your terrain selection mellow while we all gather information and let the snowpack heal. Any triggered avalanche will be capable of growing large enough to be fatal.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Snoqualmie Pass has received over 4 feet of snow since 2/11, creating dangerous Storm Slabs at all elevations. Slabs have been reactive naturally and to human triggers over the course of this storm cycle, with multiple points of failure. Strong winds near the tail end of this storm were able to transport loose snow onto leeward slopes near ridgelines to create thicker, and possibly more reactive slabs. On Wednesday, you will be most likely to trigger avalanches in wind-loaded terrain, on convex rollovers, or near rocky terrain such as cliffs and gullies. Using hand pits, test slopes, or looking for visual clues such as cracking will only key you into instabilities in the uppermost part of the recent storm snow. In order to get the full picture, you will need to dig down to the 2/11 interface to see how all of the recent snow has bonded. This interface was very reactive near the start of the storm cycle, resulting in some surprising avalanches on Saturday. If you find that the snow is unstable either near the surface or in deeper layers, dial back your terrain choices to avoid slopes over 35 degrees. 

    (2/15/2021) This skier triggered Storm Slab occurred in Kendall trees as temperatures began to warm and the snowpack started to destabilize on Monday afternoon (2/15). [Photo: Matt Schonwald]

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    The Mid-January crust/facet combo and 2/1 interface may be over 7 feet deep at this point. This may be too deep to be reactive to human triggers, but with a huge load recently added, we’re going to continue to be suspicious of these layers until we can see what happened out there. The weak structure was confirmed on Sunday and our last avalanche on this layer was less than a week ago. You should continue to stay away from big, steep, or open slopes, particularly at upper elevations. At all elevations, put a large buffer between you and large avalanche paths. This layer could possibly be activated if you trigger a large storm slab avalanche in the upper snowpack and may be more likely on slopes that get wind-loaded.

    (2/10/2021) This natural deep slab avalanche was observed from the Denny Trees area on Wednesday. It may have been triggered by a piece of cornice from above. Low Mountain, NE, 5000' HS-N-D2.5/R2-O, Photo: Jonathon Spitzer

Avalanche Discussion

Wednesday should finally give us a relative break in the weather at Snoqualmie Pass. Observations have been extremely limited the past few days, and that doesn’t come as a surprise. Heavy snow, strong winds, widespread avalanches, and uncertainty around deeper weak layers have resulted in high avalanche danger and kept most people out of the mountains. A lack of observations and such a potent storm leaves us with a lot of uncertainty, but what we can tell you is that there is a lot of recent snow, and the snowpack will need time to adjust to this load. We may have made it through the bulk of the natural avalanche cycle, but many slopes are now primed and ready for human triggers to come along. Keep your terrain selection conservative as we gather information on conditions and let the snowpack heal.

On Saturday, slabs were failing on persistent grain types at the 2/11 interface and surprising a lot of professionals and recreationalists. This layer is now around 4 feet deep, and we do not know if those grains have survived the cycle. If they have, avalanches could propagate widely, trigger remotely, or break in surprising ways. Additionally, we may get some sun-breaks on Wednesday that could help to trigger some loose avalanches. Maybe at the lowest elevations these could be wet, but most of them should be dry. Look for these on steeper slopes starting at a point near trees and rocks before fanning out as they descend. These avalanches may also be triggered by humans on steep slopes where unconsolidated snow exists. With so much recent snow, any triggered avalanche, whether it’s loose or a slab, has the ability to gauge down and entrain snow, growing large. In fact, the recent snow is a real hazard all on its own due to its depth. You can learn more about snow immersion hazard here.

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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