Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

You could still encounter unstable snow in wind-loaded areas on Thursday. Avoid features that look “fat” compared to the surrounding terrain, especially on steep convexities or near confined rocky gullies. Slabs will be thicker on the volcanoes, where more snow fell during Monday’s storm.

Problemi valanghivi

  • Wind Slabs

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

    Continue to keep an eye out for Wind Slabs near ridgelines, on convex features, or near rocky terrain such as the base of cliffs or confined gullies on Thursday. These slabs should be stiffer than the surrounding snow and could even feel hollow in places. Feel for changes in the consistency of the snow as you travel to help you identify the areas we’re concerned about. Wind-loaded features may look “pillow-like” or “fat” compared to the surrounding terrain and you might notice some textured surfaces nearby. If you suspect a slope to be wind-loaded, steer around it by choosing lower-angled terrain.

    (2/14/2023)

    A large slab avalanche triggered by a snowmobiler on 2/14. Note the convex nature of the slope and the rocks that were exposed.

    Photo: Shane Campbell

Avalanche Discussion

As we distance ourselves from our last major storm on Monday, we find ourselves in a bit of a transition period Thursday. Fresh storm snow should continue to settle and stabilize, while sunny weather will start to dissipate. We dropped the Wet Loose problem we’ve been running the past few days during the predominantly pleasant weather. This decision wasn’t made without hesitation, however. Thursday should be the warmest day of the week, but breezier and cloudier. These weather influences combined with the fact that sunny slopes have already had a chance to avalanche the past 2 days led us to drop the problem. 

On Tuesday, two avalanches were triggered in wind-loaded terrain in the West South zone. A shallower slab was triggered near White Pass by skiers in a steep gully near rocks. A deeper slab was triggered by snowmobilers on Mount St. Helens on a convex slope, exposing rocks in the process. These avalanches speak to us on two levels. One - they help confirm the variability of snow depths over the 2/13 interface in the zone. Two - they help to highlight the more likely locations for you to trigger a lingering slab on Thursday.  In the case of Mount St. Helens, this is the third time an avalanche this size has been triggered a day after a storm in the last 3 weeks. In the first instance, a snowmobiler was fully buried.

Any triggered avalanche on Thursday is expected to occur within the recent storm snow over the 2/13 interface. Near the crest, you should find this layer 5-7 inches below the surface. On the volcanoes, it will be closer to a foot down. Exposure to wind will obviously change these target depths, but you should be able to find it without much effort. Slopes that see direct sunshine will likely contain a surface crust while shaded slopes hold cold dry storm snow. 

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