Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

Recent large avalanches, a variable and complex snowpack, and tempting soft snow make a dangerous combination. Don’t try and thread the needle with these conditions. Steer away from steep open slopes, particularly on shadier aspects.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    These aren’t all your normal PNW storm slabs. Don’t run your normal playbook. Quick hand pits, uptrack tests, and small slopes could leave you feeling overconfident about conditions. 

    Human-triggered storm slab avalanches were reported in the West South on Saturday. They were generally shallow and small. Several inter-storm layers could continue to produce slides, particularly in wind loaded terrain, on very steep slopes, or near convex rollovers. These slides should be smaller and easier to manage. They could also act as a trigger for deeper avalanches. 

    At least one large avalanche failed in weak old faceted snow on Saturday. These more scary avalanches will be nearly impossible to predict. Tracks on a slope don’t mean it’s safe. Dealing with a variable and impossible to predict problem needs a more conservative approach. Keep it dialed back and stick to lower angled or treed terrain.

    (2/1/2025)

    This intentionally triggered persistent slab, propagated the entire width of the feature. It failed on facets over a thin crust. ENE, 6200ft, SS-ASc-D2-R3-O, 20-24 in deep, 200 ft wide. White Pass backcoutnry

    Photo: Dallas Glass

Avalanche Discussion

When conditions are variable like this, focus on the evidence pointing toward instability. Recent avalanches, significant snowpack test results, and a known and well-documented weak layer all indicate larger avalanches can happen. Don’t let a few tests or “feelings” sway you otherwise. 

Is this a persistent slab? There certainly is a persistent weak layer. On Saturday an avalanche professional in the White Pass backcountry was able to intentionally trigger a persistent slab that failed on facets over a crust. So far, that’s the only known slide on this layer in this zone. That could change. Prior to this storm, the January Drought Layer (JDL) consisting of facets above a series of crusts was common on W-N-E aspects. South aspects typically held sold melt-freeze crusts. 

This storm has been impressive for the zone. Snow totals range from 10-24 inches and counting. As this storm winds down, cold temperatures and fluffy snow could make dry loose avalanches (sluffs) more common. These could even run in the trees.

At lower elevations, storm totals aren’t as significant. While it’s improved travel, “scratchy” seems to be the word often used. Avalanches down low should be smaller and confined to very steep terrain.

Régions couvertes