Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Highlights

Very dangerous avalanche conditions will continue on Monday at Snoqualmie Pass. Slides will be very large and capable of running long distances toward valley bottoms. Stay away from all avalanche terrain until this storm is over.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    If there is a time for the deep persistent layers we have been talking about to come to life, it will be on Monday. There is a possibility that we could reach Extreme avalanche hazard if freezing levels are higher than predicted and we receive rain at upper elevations. If this happens, avalanches may break mature trees and be historically large. The Mid-January crust is now close to 7 feet down and the 2/11 layer is closer to 4 feet down from the surface. Uncertainty about if the input from this storm will be enough to tip the scales on these layers has us on edge. Regardless of the rating, these layers should shape your mindset for tomorrow and you shouldn’t go anywhere near avalanche terrain. The potential threat is too high to risk it.

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

  • Storm Slabs

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

    Above the rain/snow line, heavy snowfall and strong winds will help to overload the snowpack and trigger large to very large natural avalanches. These slides could fail on storm instabilities from this past week or at the new snow interface. Areas that are susceptible to wind-loading will have thicker and possibly more reactive 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. Monday is not a day to be anywhere near where avalanches can run or stop.

    (2/20/2021) This intentionally triggered storm slab occurred on Saturday near Gold Creek. W, 3800'. SS-ASc-D1-R2-N, 6-8" deep, 20' wide

  • Wet Slabs

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

    Below the rain/snow line, heavy rain will continue to destabilize the snowpack in a number of ways on Monday. Some areas will have already seen rain and natural avalanches occur before daybreak, while other areas will see rain for the first time as freezing levels creep up. Just because a path has already slid, doesn't mean that it can't slide again. There are multiple crusts and layers of cold dry snow at all elevations for water to pool on and break the snowpack’s bonding. As the amount of liquid water added to the snowpack increases, you may first witness Wet Loose avalanches before later seeing slabs release at some of these layers of concern. Glide avalanches could follow on smooth rocky, unsupported slopes. The timing of wet avalanches is very difficult to predict and they can act in surprising ways. Although we can’t predict the exact timing, we can tell you that they will occur on Monday and you should stay out of avalanche terrain at lower elevations.

    (12/21/2020) Example: This large wet slab occurred during a rain event earlier this winter.

Avalanche Discussion

The scariest part of this avalanche cycle begins on Sunday night and will continue into Monday. As noted above, we are teetering on Extreme avalanche hazard due to a weak snowpack, lots of recent cold snow, a forecasted warm-up, strong winds, and heavy precipitation - both liquid and solid. We don’t have the direct observations or recent avalanche occurrences on those deeper layers to put us at Extreme. That said, there will be several rounds of natural avalanches and we expect very large (D3) slides to occur on Monday. We could have forecasted 8 of the 9 avalanche problems for tomorrow and probably have been correct. With a complex snowpack and overlapping avalanche problems, it really doesn’t matter what color the map is, just keep it simple and stay away from the mountains while this one 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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