Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Thu
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Wind slabs lurk on steep convex slopes near and even well below ridgelines. Navigate around these potentially wind-loaded areas. Meanwhile, keep an eye on the sun and adjust your aspect when warming temperatures produce roller-ball activity, a precursor to potentially large loose wet avalanches . 

Problèmes avalancheux

  • Wind Slabs

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

    You are most likely to trigger a wind slab above treeline, where cooler temperatures and stronger winds aligned at the outset of Monday's storm to transport signicant snowfall. However, you can still trigger one near treeline. An OBSERVATION depicts several slab avalanches that released naturally, well below ridgeline during the storm. Reactive wind slabs are expected to linger another day in especially wind-loaded locations just below ridgelines or cross-loaded terrain features and might be triggered on steep, convex rollovers such as in the observation.  They will be slower to heal on colder, shaded aspects. Trying to determine which slopes were loaded by the strong winds at the start of Monday's storm may not work with lower density snow covering up the usual visual clues.  Be suspicious of slopes below recently formed cornices. Feel for firmer wind-stiffened snow and watch for cracking of snow surfaces as clear signs of instability and a message to stick to lower angle and lower consquence terrain.

    Consider your overhead exposure as well - you might be in the shade but as the sun climbs and snow sheds from rock faces, think about natural avalanches that could be triggered from above.  Fresh cornice development or loose wet avalanches may release due to the warm temperatures on connected slopes and could trigger wind slabs on the slopes below.

    (12/1/2020) These slabs released naturally on steep, convex rollovers during Monday's storm. Similar features might be triggered on Wednesday.

  • Loose Wet

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

    Wednesday's forecast is for sunshine with temperatures warming into the 40's at most elevations after a cool start below treeline.  While Tuesday stayed cool enough to inhibit loose wet avalanche activity, we think the warmth will be enough to destabilize slopes on Wednsesday. These avalanches will release on steep, sunny slopes from late morning into early afternoon.  While most will be small, they can entrain to the depth of recent dry, unconsolidated snow to become large. Move off steep sunny slopes by late morning and think about the terrain above and below you. 

    Ex: Be on the look out for loose wet avalanches, particularly below rocky outcrops and stands of trees.

Avalanche Discussion

The Mt Baker area received 12-16" of snow from Monday's storm. Strong winds that were seen during the first half of the storm backed off toward the end while impressive hourly snowfall rates continued through Monday afternoon.  On Tuesday, recreationists triggered small wind slabs involving the storm snow, but professionals witnessed less avalanche activity than expected with limited propagation. Cooling temperatures during the storm likely rendered the slabs less reactive.  Over the weekend, the West North zone saw several shallow human triggered soft slabs and one larger natural avalanche release in the Table Mt area. 

Snow depths range from 40-65 inches throughout the North Cascades, and continuous snow begins near 2500-3000ft. Snow coverage is well above average for this time of year, but early season conditions still exist. Stay alert for open creeks, tree wells, crevasses, or other exposed hazards. Consider the consequences when choosing terrain. Falling or getting caught in even a small avalanche could result in a rough ride.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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