Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Recent avalanches, weak snowpack structure, heavy precipitation, mild temperatures, and strong winds all point towards one thing; very dangerous avalanche conditions. Stay away from anywhere an avalanche can start, run, or stop.

Avalanche problems

  • Persistent Slabs

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

    This storm on its own would likely produce significant avalanche activity. As it combines with a weak snowpack structure you could see surprising slides that trigger remotely, step-down into older snow layers, and run far distances. On Thursday, three separate groups of professionals reported avalanches failing just above the 2/1 crust. These thin slabs propagated widely across features. By Friday morning this same weak layer will be 18-24” deep and much more concerning. Stay away from all avalanche terrain including areas where avalanches run and 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.

  • Loose Wet

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

    The forecast shows the rain-snow line should stay just above pass level more much of the day. As a result, expect a wet and punchy snow surface that could produce natural loose avalanches. Closer to the rain-snow line these slides may entrain significant snow and grow large. Stay off of and out from under very steep slopes, especially during periods of heavy precipitation.

    (12/18/2020) Example: This loose wet avalanche was triggered by a tree bomb on the Alpental Rd.

Avalanche Discussion

The current weather and snowpack setup check all the boxes for a natural avalanche cycle. While the heaviest precipitation may occur before dawn, loading should continue into the day along with natural avalanches. A weak snowpack structure has been well documented through numerous observations across the zone. We expect this storm to tip the scales and cause avalanches on these buried older weak layers. 

Currently, two layers of concern exist in the upper snowpack. 1). A thin crust (2/1) with weak snow above and below. In some cases, facets and/or surface hoar were observed at this interface. Natural and triggered avalanches occurred on this layer Thursday. As it gets buried deeper it could become more reactive and produce large avalanches. 2). The 1/13 crust and facets now lay deep in the snowpack (3’ or more by Friday morning). So far, we have not seen significant avalanche activity on this layer. However, it has been very active in adjacent forecast zones. You could trigger avalanches on this layer or shallower slides might step-down and fail on these weak old snow grains. 

Snow pits and snowpack tests serve as great tools for tracking these persistent layers but don’t overlook the critical “red-flag” data. Recent natural and triggered avalanches, persistent grains, in the snowpack, significant loading, strong winds, and relatively warm temperatures all indicate unstable snow.

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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