Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

Avoid travel in all avalanche terrain. This includes lower-elevation areas that can be overrun by avalanches from above. Heavy rainfall will further weaken the snowpack and spur a round of wet avalanches. Danger will be greatest in the morning before rain turns to snow but plan around dangerous conditions for the entire day.

Problèmes avalancheux

  • Glide Cracks

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1.5–2.5

    Glide avalanches occur when the entire snowpack slides on the ground below. Rain will weaken the bond between the snowpack and the ground and make these much more likely. In addition to glide, expect to see some combination of wet loose, wet slab, and cornice fall avalanches depending on the terrain.

    It’s nearly impossible to say which snowy slopes will produce avalanches or when they will happen. You are most likely to see natural avalanches during or immediately after periods of heavy rainfall. But glide avalanches can still release well after it stops raining. The best plan will be to just avoid traveling on or under big slopes, or any terrain with overhead hazards. 

    (12/4/2024)

    Look for rocky features big and small to shed more snow with heavy rainfall.

  • Storm Slabs

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

    We all anticipate the end of warm weather and rain and a return to snowy conditions. As the snow starts to pile up, look for instability in the layers of new snow using hand shears, test slopes, and other simple tests. Shooting cracks are a sign you could trigger an avalanche if you head onto a steep slope. You are most likely to trigger a fresh slab in wind-loaded terrain, but consider all slopes suspect until proven innocent. 

    You are more likely to trigger small slab avalanches like this when fresh layers of snow are poorly bonded together.

    Photo: Irene Henninger

Avalanche Discussion

Rainfall events can present a challenge for avalanche forecasting in this part of the Cascades. A cold, dry snowpack combined with copious rainfall is a tried and true recipe for avalanches. But sometimes the snowpack has already seen significant warming or rain. Maybe the transition from rain to snow is unknown, so you don’t know how much liquid water will fall from the sky before it turns white. It would be nice to think every rain event will produce big avalanches, but it’s also possible you could see much less natural avalanche activity than expected.

In this case, the snowpack might actually absorb the forecast water amounts quite well, but based on observations in other zones, there is a lot of snow ready to peel off rock faces around West Central. These falling blocks of snow and glide avalanches might start to gouge out wet snow lower on the slope and make some big, big piles in the flats below. While you might not experience High danger and widespread natural avalanche activity, it would be best to start the day with the mindset that High danger requires - avoiding all avalanche terrain.

 

Régions couvertes