Bulletin d’avalanche

Olympics

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Wind slabs may be more reactive than you would expect given the relatively small amounts of new snow and wind loading. Although slabs within the new snow may not be large enough to harm you, on steep terrain in the lee of ridgelines, they could break down to an old snow interface around 1 ft down. 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Reports of weaker interfaces about 10-12" down and another 2 inches down should have you especially alert for wind slabs. Why? The former has generally not shown full propensity to propagate, but perhaps could with additional wind loading. The latter needs a slab on top of it and with only an additional 2-3" of snow expected, that means we need winds to generate a 6" snow within the new and recent snow. These slabs are most likely to lurk on the lee sides of ridgelines. And you're most likely to trigger them on slopes steeper than 35 degrees or where there slope steepens below you. Use more conservative entry points if you recreate on wind-loaded aspects. Observe changes in the snow surface for signs indicating how far down the wind loading extends on the slope. Lastly, check the reactivity of snow within the upper 2 ft of a windloaded test slope and dial it back if the slab propagates in an ECT.

    (1/2/2025)

    Example from the West South zone: Obvious signs of wind transport along this exposed ridge pointed toward potentially loaded slopes. 

    Photo: Dallas Glass

Avalanche Discussion

Observers found buried may have found buried surface hoar at the 1/3 interface with 2" of lower density snow above it. Expect 1-3" more of snow above this by Sunday. Below this, snow gradually incrased in hardness to 4F above a layer of feathery buried surface hoar around 8-12" below the snow surface. This layer was reactive in CT and shovel tilt tests on shaded aspects, but didn't fully propagate across the column. It wasn't reactive on southerly aspects.  If an avalanche were to fail on this lower weakness, it would be a hard slab, breaking more widely than you expect. Therefore, it's a good idea not to trigger one. The best way to stay safe is to avoid triggering a surficial wind slab that stress this layer or result in a slab that steps down. You can read more about the interfaces in question from Saturday's observation and a 12/30 observation. The observers also noted a crown from an older avalanche that appeared to have been triggered by cornice fall above extreme terrain.

If you do find evidence of more widespread reactivity than we expect on Sunday, don't hesitate to dial it back and give steep open slopes some space.

On Friday, NPS Rangers reported a layer that failed around 1 meter down on a density and grain interface. This layer didn't propagate. A party on 1/2 may have identified an older wind slab that retained some reactity about 1.5 ft down. Such an older wind slab should be gaining strength, but it's not a bad idea to have a look before committing to a steeper slope on Saturay.

Ample snow cover makes for easier travel above 4000', however near this elevation, holes, creeks, and other obstacles quickly impede easy navigation. 

You'd expect to find cracking, whumphs or potentially small natural avalanches in actively wind loading terrain.Prior to this storm, 

Share what you see and submit an observation!

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