Avalanche forecast

Olympics

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
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Out of date — this forecast expired 4 years ago.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

This is not your typical Moderate danger day due to the presence of a reactive persistent slab.  You can trigger a widely propagating and consequential avalanche on any open slope steeper than 30 degrees. Terrain selection puts control of the problem in your hands - traveling along ridgelines, through dense trees, or on smaller slopes of limited consequence. 

Avalanche problems

  • Persistent Slabs

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

    On Friday (12/16), an excellent observation confirmed the existence and reactivity of a slab overlying surface hoar buried 12/8. A column test near treeline in North Bowl failed on isolation on a thin gray line of surface hoar 15" below the surface. Test results on a SE aspect were more variable but still showed some reactivity. These results suggest the continued potential for human-triggered avalanches nearly a week after the last storm. Last weekend, the same layer was the culprit for a D1.5 natural avalanche (12/10) in Poma Bowl and a D2 remotely triggered an avalanche on a NW aspect at 5200 ft (12/11). These avalanches had all the hallmarks of failure on persistent grains. You don't want to get caught in one of these avalanches as the slab may be 1-2 ft deep in more deeply wind-loaded terrain. Buried surface hoar maintains notoriety for producing avalanches that can release on a low-angle slope, break above you, propagate widely, or trigger remotely as we have already seen.  Observations on this layer remain limited, leading to uncertainty of the problem's distribution. You should assume it exists throughout the terrain at this time. There's an old adage that when uncertainty increases, your terrain selection goes down. For this reason, we recommend more conservate terrain selection than you would normally choose on a Moderate day.  Stick to ridges, thick trees, and slopes less than 30 degrees to maintain a margin of safety. Give space to steeper, unsupported, or actively wind-loading slopes where the hazard will be most elevated. Whumps and rumbling collapses provide a warning that the risk of triggering an avalanche on a steeper slope nearby may be higher than forecast.

    For those that engage with avalanche terrain, recognize that you are accepting a lower likelihood, but higher consequence risk. You can use snow profiles and snowpack tests to confirm the presence of this layer, but they don’t prove its absence. Limit your risk as much as possible, by choosing smaller terrain features with friendly runouts (as opposed to terrain funnels or traps). 

    (12/10/2022)

    Natural soft slab running on surface hoar. Poma Bowl, Hurricane Ridge.

    Photo: NPS Olympic Rangers

Avalanche Discussion

These are not normal conditions at Hurricane Ridge and you can't expect the instabilities to change much through the weekend.

This is the time when we really need your observations. If you head out, did you find the slab/weak layer structure intact? Could you see a thin, grey line? Was it reactive? Saturday might be the final day to track snow surfaces to determine what might get buried when light snow starts falling and you can help us here as well. 

Even though it feels like winter, plenty of exposed and shallow buried obstacles still exist to make travel more challenging and potentially dangerous.

Regions covered