Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

A major winter storm and a known buried weak layer could create very dangerous avalanche conditions across the West South zone Saturday. Natural avalanches are expected, especially in the morning hours. If you decide to brave the storm, steer around all open avalanche slopes near and above treeline.

Avalanche problems

  • Storm Slabs

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

    As if the high precipitation rates and significant snowfall weren’t enough to build very dangerous conditions, strong winds and a known buried weak layer (read the discussion for details) could push the snowpack past the brink. We’re expecting a natural avalanche cycle overnight. However, because significant snowfall will persist into Satuday morning, so too could the very dangerous conditions. Give this storm and avalanche cycle time to play out away from slopes where avalanches may start, run, and stop. 

    At lower elevations, and in locations that receive less than a foot of snow, conditions will be slightly less dangerous. In these areas use small slopes and uptrack tests to see how the snow reacts. If it fails easily or cracks, avoid nearby slopes over 35 degrees.

    (12/8/2022)

    A small shallow human-triggered slab in the Crystal Mt backcountry Thursday 12/8.

    Photo: Shane Robinson

Avalanche Discussion

Timing: With the heaviest precipitation expected overnight, we anticipate a natural avalanche cycle. However, different locations within the zone could reach their tipping point at different times. In some areas, large natural avalanches may still occur in the morning. As the day goes on and precipitation slowly tapers, the avalanche danger could slowly decline. 

Location: This weather pattern favors the volcanoes and Crystal Mt. Mt St Helens could easily receive 2.5-3.5 in of precipitation by Saturday afternoon. In these areas, you may find 15-30 in of new snow before the sunsets. Needless to say, avalanche danger could remain very dangerous for the locations where the storm continues to rage. For White Pass and Government Meadows, we expect less snowfall. In these areas, the avalanche danger may be locally lower. 

Persistent Weaklayer: On Friday an NWAC Forecaster and avalanche professionals observed buried surface hoar at Mt Rainier and near Crystal Mt. It was also observed at Mt Hood and Stevens Pass. This leads us to believe it likely exists at Mt St Helen, Mt Adams, and possibly White Pass. In all instances, observers noted the layer failed and propagated in snowpack tests, but had not yet produced any known avalanches. This storm could change that equation. Avalanches failing on persistent grains may fail very easily, trigger remotely, and wrap around terrain features. The buried surface hoar was typically found 10-20in (25-50cm) below the surface prior to this storm on all aspects near treeline. Avalanches involving this old layer would likely be large and deadly. 

Even though it looks and feels a lot like winter, early season conditions still exist. Don’t let your excitement for the soft snow carry you into open creeks, holes near rocks, or shallowly buried trees.

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