Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
2 · Modéré
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

Avalanche danger will increase as the storm arrives, with 6-8 inches and strong winds forecasted through the afternoon. As more snow accumulates, start paying attention to thicker wind-drifted deposits. When you find wind-loaded drifts of snow breaking and sliding in large pockets on steep slopes, avoid those areas.

Problèmes avalancheux

  • Wind Slabs

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

    New wind slab problems will develop in the afternoon. Strong winds will quickly redistribute the freshly-fallen snow, and human-triggered wind slab avalanches will be likely by the end of the day. In addition to the rapid change we’ll see over just a few hours, new snow, especially at first, may struggle to stick to the old snow surface. This will especially be the case in the thicker wind deposits. 

    Expect to find drifts along ridgelines, in gullies, and around rock features. Identify areas of wind loading and feel for changes in the snow surface. Pay attention to cracking and other signs of weakness such as whumphs.   When you find these characteristics, steer around slopes greater than 35 degrees or shift to terrain where wind loading hasn’t occurred.

    Windy conditions will develop fresh cornices and load slopes near ridgelines. This shallow slab was likely in wind-loaded terrain.

    Photo: Dallas Glass

  • Persistent Slabs

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

    Our concerns around the persistent weak layer haven’t gone away yet. It has been several days since an avalanche was reported on this layer, but with new snow (weight) added to the snowpack we may see avalanches on the layer again. 

    • The layers are most prevalent on shady aspects above 5400 feet in elevation.  
    • There is around 2  feet of new snow above the weak layer.
    • Observed avalanche sizes are ~D2.
    • Snowpack tests produce inconsistent results, sometimes even in the same snowpit.
    • Many steep slopes where riders got out on with no results saw nearby slopes or another location on that slope avalanche on the weak layer. 

    Although the likelihood of triggering one of these avalanches is low, the consequences could be high if you are in a consequential spot in the terrain. Remember, persistent slab avalanches can be triggered from low on the slope or remotely.  Factor in what would happen if you trigger a large avalanche on the slope you’re thinking of getting out on.

    (2/12/2022)

    Natural avalanche suspected of failing in January 30th crust-facet layers. Estimated date of occurrence between Feb 8th-11th. East-northeast aspect at 6200' or Mt. Baker/Schriebers.

    Photo: Graham Clark 

    Photo: Lee Lazzara

Avalanche Discussion

The incoming storm starts by hitting the West North zone hardest on Saturday before shifting its intensity further south into Sunday. Expect to see another 6-8 inches and strong winds continuing overnight. Snow will continue redistributing into more reactive slabs through the weekend. 

All of a sudden we’re back to winter with cooler temperatures and fresh snow. The good thing about this storm is that aside from locations with the persistent weak layer, our avalanche concerns are primarily limited to the new snow layers. This problem is relatively shallow and easy to identify. With serious melting occurring in recent weeks, don’t forget about the crusty, variable surfaces beneath the new snow while you’re out on Saturday.

Régions couvertes