Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Downwind slopes hold slabs of wind drifted snow that could be triggered in steep, unsupported terrain. Shallow new slabs might also form near ridgelines. Identify and navigate around steep wind loaded features on lower angle, planar terrain. 

Problèmes avalancheux

  • Wind Slabs

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

    As the current crop of wind slabs gains strength, places where you can trigger one become more isolated. If you do trigger one of the older, deeper slabs on Tuesday it will likely be on a convex rollover, a gully wall, or around a cliff or rocky outcropping. A skiff of new snow and moderate ridgeline winds could make shallow new slabs as well.

    Tune into the pattern of wind loading by using blowing snow, scoured snow surfaces, cornice-like features, and changes in snow texture to figure out where wind slabs might lie in wait. Use small test slopes to get a read on how wind slabs hold up under load. Small hand pits can give a sense of how wind slabs are bonded to the layer below.

    Small wind loaded features at ridgeline can serve as test slopes to gauge the reactivity of fresh wind slabs.

     

Avalanche Discussion

Late Sunday brought a report of a snowmobile triggered avalanche on Mt. St. Helens where the rider was caught and buried over 6’ deep. Rescuers were able to successfully extract the rider and no significant injuries were reported. More information is available here.

Widespread sun and wet loose avalanches are not expected Tuesday. If the sun does make an appearance keep an eye on terrain overhead that is warming up and producing rollerballs or very small loose wet avalanches.

Last night’s weather forecast generally met expectations today. Moderate westerly winds were recorded across the zone and near-freezing temperatures prevailed near treeline. A bit of an inversion was seen midday with temperatures in the high 30’s at upper elevations. Skies went full bluebird in many areas by lunchtime but clouds started to thicken again mid-afternoon. No avalanche observations were submitted Monday so the size and extent of wet loose avalanches are unknown. 

The current snowpack below the most recently formed wind slabs consists of alternating layers of rounded grains and rain crusts. Buried surface hoar and/or facet layers that previously produced avalanches have been dormant and likely rounded out. The biggest question mark is if weak snow surfaces from late last week were preserved intact under the new snow. Take an extra minute or five to look at the interface between new and older layers before diving into consequential terrain. 

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