Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Strong winds will create unstable slabs of wind drifted snow near and above treeline. Identify and avoid steep terrain where dense slabs are forming below ridgelines and other terrain features.  Conditions could be different than expected due to uncertainty about snowfall amounts on Wednesday.

Problèmes avalancheux

  • Wind Slabs

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

    A combination of new snow and strong ridgeline winds will build fresh wind slabs. They may be more pronounced in the north end of the zone where wind speeds and new snow amounts could be higher. Be prepared for greater danger in all areas if new snow is deeper than forecast. Be ready to adjust your plan toward less wind exposed and lower angle slopes.

    Use caution as you ascend into wind affected terrain. Use cornices, scoured ridgelines, and drifts behind objects to identify areas that hold wind slabs. Test slopes and hand shears can help you evaluate slab reactivity on small, non-consequential terrain features. 

    (12/20/2021)

    Scoured ridgelines and cornices indicate the typical direction of wind loading.

    Photo:  Lee Lazzara

Avalanche Discussion

Several days of stormy weather are in the forecast for the Cascades with continued snowfall and periods of strong wind, potentially through Christmas. New snow amounts vary widely from south to north in the West Central and also with weather forecast uncertainty. Areas near Stevens Pass could see as little as a few inches as opposed to 2’ or more as one travels closer to Highway 20.

Clear night skies and light winds in the northern end of the zone may have created a weak snow surface of surface hoar or small facets. In some regions, these weak snow grains were severely damaged by a rise in freezing levels on Tuesday and accompanying light rain. Despite the latter observation,  new snow falling on surface hoar or facets is still a point of uncertainty and could enhance avalanche danger in the coming days. 

Reported avalanche activity was minimal since the natural avalanche cycle on December 18th. Human and snowmobile triggered wind slab avalanches were reported on the 19th around Mt. Baker. Small loose wet avalanches related to periods of clear sky and strong sun were reported the same day and also on Monday the 20th.

Régions couvertes