Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

It's going to warm up during the day and your largest avalanche concern will be wet loose avalanches running in the snow surface. These are most likely to be a problem where the snow was previously dry and low density, so shadier mid to upper elevation aspects are where you could have the highest chances of encountering these avalanches. If snow surfaces become wet and heavy or if you notice rollerballs or small slides running down, stay off and away from steep snow-covered slopes. 

Problèmes avalancheux

  • Loose Wet

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

    Forecasts call for overcast skies and a freezing level rising to about 6000ft on Sunday before temperatures cool and our next storm hits Sunday night. With such warm temperatures and overcast skies, "greenhousing" might come into effect, where the sun's warmth is trapped beneath the clouds, and all aspects moisten. If this occurs, areas with previously cold dry powder will be most affected. Below treeline terrain is mainly crusty or previously affected by rain, so there shouldn't be much soft loose snow that will slide with warming. Consider a higher likelihood of wet avalanches if you find more than a few inches of new snow below treeline.

    Look for pinwheels or balls of snow rolling down the slope as telltale signs of warming. Small wet loose avalanches could be a sign larger ones are not far behind. If you travel out onto a steep slope when it is moist and you're sinking in more than a few inches, there is a good chance you could trigger a slide beneath you. Slides might occur naturally if the snow gets wet and heavy enough. They probably will not be large enough to bury and kill you, but these wet loose avalanches are still not something you'd want to get caught in, especially if they send you into a terrain trap. 

    The energy balance has to be just right for greenhousing to occur, and we're not quite sure whether there may be less avalanche activity, or more, on Sunday. We may just get heavy sticky snow rather than avalanches. Despite being unsure of the extent of avalanche activity, the best way to manage it is to continuously pay attention to the snow beneath and around you, and when you start noticing those previously mentioned signs of the snowpack losing strength and warming, start shifting your travels to lower angle terrain and away from beneath steep, large slopes. 

    Rollerballs and small wet loose avalanches similar to what you might see on Sunday. Avoid traveling on or under steep slopes if you see this. Photo: Andrew Kiefer

Avalanche Discussion

Avalanche conditions differ across the various frontiers of the West Central zone. Storm and wind slabs were generally smaller and less reactive further south and east. It's a different story to the north where there was more snow and rain, more wind, and more avalanches in the last week. Most relevant is an unusual pattern of avalanche activity reported on February 8th in the West North zone (obs, obs). These avalanches were large, surprising, and quite dangerous.  One was triggered from low on the slope. They are not typical wind slabs but they occurred in obviously wind-loaded terrain. No injuries were reported but in one of the avalanches the rider was buried with a hand exposed and promptly dug out. 

No avalanches like these were reported anywhere else on the west slopes. However, there is a lot of big alpine terrain in the West Central zone that could hold a similar snowpack - a layer of facets and thin melt-freeze crust buried anywhere from 1-4 feet deep. You are most likely to find this setup in the farthest northern and eastern alpine areas of the zone.

Pits may or may not do much to help you gauge if the slope in front of you is good to go. If you head into steep, wind-loaded terrain above treeline you might simply be assuming a bit more risk than usual.

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