Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

There are 2-3’ of new snow in the mountains - deep snow and windy conditions could be difficult to navigate and extra caution is required for backcountry travel.  Avalanches are likely in areas where the wind is transporting abundant new snow onto downwind slopes. Be extra vigilant where you could fall into a tree well or some other terrain feature where you could get trapped in deep snow. Travel with a partner and keep them in sight at all times.

Problemi valanghivi

  • Wind Slabs

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

    Gusty winds and plenty of light-density snow equal fresh wind slabs. Easterly winds often come with an unusual pattern. Some mountains and ridges will see sustained strong winds - with lots of wind transport and slab formation - while other areas might remain calm. Look for the strongest winds to occur in the Mountain Loop, near both Passes, and along the crest. Avalanche danger near treeline is less where wind loading is less pronounced.

    Blowing and drifting snow will point the way toward slopes that are actively loading and building fat, smooth-looking slabs. Scoured ridgelines and other wind affected features can also reveal wind slab hideouts. Shooting cracks are a red flag that you have found an area of unstable slab. When in doubt just avoid steep terrain with recent wind loading no matter how big or small the slope.

    Signs of wind loading to look for Saturday.

    Photo: Dallas Glass

  • Loose Dry

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

    It just keeps snowing. You will likely see some sort of new snow avalanche in steep, wind sheltered terrain Saturday. These smaller avalanches will likely sit somewhere on the scale between dry loose and very soft slab avalanches. They shouldn’t present a serious danger on their own but it could be a different story with terrain traps below or on big, steep slopes where they can run far and entrain more snow.

    These kinds of avalanches shouldn’t take you by surprise. If you get into steep terrain some amount of snow will probably come down the hill with you. Look out for shallow slabs forming at the surface if loose snow becomes cohesive during sun breaks or with more warming than expected.

    (2/26/2023)

    Example of a human triggered dry loose avalanche in Swfit Creek just outside of the ski area boundary.

    Photo: Zack McGill - Cascade Mountain Ascents

Avalanche Discussion

While the danger from slab avalanches is mostly limited to wind affected terrain, conditions could be considered dangerous purely on the amount of new snow out there.  It won't take much wind, warming, sun or to set things off and produce natural avalanche activity. A smaller avalanche could step down to a deeper layer and produce a larger avalanche where a layer of graupel, small faceted grains, or even weak new snow has not fully rounded out.

A few naturally triggered slab avalanches were reported from both Steven and Snoqualmie Pass. Slabs formed out of the dry loose snow in wind affected terrain or where sun breaks allowed the snow surface to warm and stiffen up

An observer in West North found 8-12” of new snow near treeline with near bottomless recent snow below. Ski penetration was measured at 2’ and stepping off your preferred method of floatation resulted in near burial. No signs of instability were reported. Testing showed the potential for propagation at slight density changes within the recent storm snow. Avalanche mitigation work produced loose snow and very soft slab avalanches running fast and far on steep slopes. No other slab avalanches were reported but visibility was too poor to see much. 

 

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