Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You can easily trigger large avalanches on weak snow at the base of the snowpack. Northern aspects above 5000ft are the most likely area to find these dangerous conditions. These avalanches may be up to 3 feet deep, potentially even deeper in areas where the winds have drifted snow. Whumphing collapses under your skis, feet, or equipment are warning signs to stay on low angle terrain. You can anticipate this problem to linger for a while as these weak, surgery snow grains are slow to heal.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2

    Currently, the snowpack is sending clear signs of danger, and observers across the East Central Zone from Mission Ridge to Holden are reporting loud audible whumphs and shooting cracks. At the base of the snowpack, an old layer of facets and surface hoar are the culprits. Avalanches have been running down to the ground on these layers in and around Mission Ridge. These types of avalanches are slow to heal, and conditions remain touchy. You could trigger avalanches 1.5-3 feet deep, and slides may run on the rocky ground, increasing the consequences further. You can trigger these avalanches remotely from low angle terrain below steep slopes or from adjacent slopes, so be sure to keep tuned into the surrounding terrain. Be especially suspicious of large, steep slopes and areas with stiffer wind drifted snow. Areas above 5,000ft that face NW-NE may be the most likely place to trigger this deeper weak layer. However, folks are finding signs of instability even as low as 3,600ft in old clear cuts on north aspects.Evidence is increasing that this weak layer may not be a problem on SE and SW aspects, but we need more information to boost confidence.

    Example persistent slab avalanche from the Salmon la Sac drainage in 2021. Photo: Matt Primomo

Avalanche Discussion

Evidence of this reactive layer keeps piling up as avalanche professionals, and winter recreationists continue to report collapsing and cracking. Patrol at Mission Ridge has reported another touchy day on Saturday in terrain without previous avalanche control efforts. These slides ran on a thin crust from around 11/25, and many stepped down to or ran on the ground (or on basal facets from 11/22). On Thursday in Icicle Creek, there were multiple reports of whumphing tied to basal facets (11/22) in locations as low as 3,600ft on North facing slopes. Observers at Holden and Dirtyface also reported some whumphing on these deeply buried weak layers. All of this is strong evidence that this layer is not ready to be trusted yet, and could produce surprising and wide avalanches. 

It's still early season, and the snowpack is relatively shallow and unconsolidated. With deep, unconsolidated snow out there, make sure to stay within earshot or visual of partners. Tree wells are open, and plentiful buried snags, creeks, and rocks exist. If you are out and about in the mountains, let us know what you find by submitting an observation.

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