Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Thu
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2 · Moderato
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2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Wind-drifted snow near the top of mid-elevations and at upper elevations could avalanche with a human trigger. A few inches of snow during the day may hide larger preexisting slabs that formed Christmas night. Identify wind-drifted snow features, where the snow is heavier and deeper, and avoid these features on steep slopes in areas where there's greater than around 6" of dry snow at the surface. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Thick, large slabs deposited in unusual locations exist at upper elevations and possibly the upper reaches of mid-elevations. It's possible that the weight of a human could trigger an avalanche on one of these wind slabs. The slabs formed just over a day ago with extreme wind, so they may be found lower on a slope or drifted into unusual areas.

    We're not quite sure how reactive these slabs may be, and we have limited information from upper elevations. Be prepared to evaluate conditions for yourself if you make it this high. Due to to intensity of the winds, the slabs could be quite firm. You might not find yourself sinking into them at all. Just because surfaces may be relatively hard, it's not a guarantee that you couldn't find a spot where you could trigger an avalanche. Dig down to underlying layers and evaluate the bond beneath the new snow layer. If a stiffer slab is sitting over a softer layer of snow you might be able to trigger an avalanche.

    A few inches of snow is forecasted to fall during the day Wednesday. It'll still be windy, but this new layer could disguise underlying slabs, or could form newer and more reactive shallow slabs. When you find more than about 6" of dry snow over underlying layers, start on small slopes before stepping out onto larger ones. When in doubt, steer clear of wind-loaded slopes steeper than 30°. 

    Example photo: A slab avalanche that failed in a wind-loaded area. Note the cornice above, a clear sign that wind loading occurred on the slope. Schreibers area. This is similar to what you might see on Wednesday. 

    Photo: Graham Clark

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Snowline for Wednesday's precipitation may hover at a similar elevation to the Christmas storm, within the mid-elevation band. Wet new snow layers may rollerball and could produce small wet loose avalanches on steep slopes. If you see rollerballs or small wet loose avalanches, avoid large and steep slopes nearby. 

    Continued small, shallow snowpack shedding events may occur on steep, smooth slopes in areas where a fully saturated snowpack exists. 

    Example photo: Rollerballs in the new snow may lead to small wet loose avalanches. Bearpaw area. Photo: Andrew Kiefer

Avalanche Discussion

The Christmas storm dropped over 2 inches of water since midday on the 25th and through much of the night. Wind gusts were in the 50mph's for a few hours during peak snowfall instensity. Four inches of slushy snow was reported at 5,000ft, which resulted in "good skiing".  We aren't exactly sure of the elevation where there was remarkably more snow, but we suspect it's somewhere in the vicinity of the transition between mid and upper elevation bands.  At some higher elevation, probably above at least 6000ft or so, the storm equated to about 2ft of highly wind-affected snow. 

Before the Christmas storm, around 6 inches of wind affected snow exists from the previous week at mid and upper elevations. Beneath that layer, a crust exists. From there to the ground, snow layers are moist with varying crusts, from at least 5000ft and lower. We don't expect avalanche activity to occur beneath the crust in areas where the crust hasn't been completely softened by the warm temperatures and rain. 

As is the trend for this year, beware of early-season hazards like shallowly buried rocks and roots, and open creeks. Don't forget there's an extremely variable crust under the new snow layers, and it may be exposed in some locations due to the extreme wind. Snow at mid and lower elevations will likely be punchy, possibly down to the ground, if you're on foot. If you make it out, especially to upper elevations, we'd love to hear from you! Please submit an observation using THIS link, or better yet, use our app, Avy. 

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