Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Peligro de aludes

Thu
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You can trigger avalanches in areas where the winds have built deep drifts of snow. These slabs may step down to deeper weak layers in areas around Blewett Pass and Mission Ridge. Identify slopes with stiff snow layers over soft layers using your probe or ski pole, and pay attention to warning signs such as audible collapses in the snowpack or shooting cracks in the snow. These are signs you should travel in wind-sheltered areas or low angle slopes. 

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Moderate westerly ridgeline winds picked up on Tuesday and will continue overnight and into Wednesday morning. As a result, wind slabs formed at the base of cliffs, lee aspects of ridgelines, and in gullies where the wind blows across the slope. There is potential for these wind slabs to step down to deeper weak layers, creating a large and dangerous avalanche.

    Surface texture can help you identify wind affected terrain, even from a distance. A rippled surface indicates that the winds have been drifting snow into slabs. Look for signs of blowing and drifting snow and use small hand pits to identify stronger layers of wind-driven snow over soft powder snow. Cracks shooting out from your skis, snowboard, or equipment and loud whumphing collapses are a sign that steep slopes could avalanche. 

    (12/3/2022) An example of a shooting crack in a wind-loaded pocket. One of the red-flag signs of instability that shouldn't be ignored. Also, take note of the rippled looking surface indicating wind affected terrain.

    Photo: Dallas Glass

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    It has been a week since the last significant loading event, and red flag observations of collapsing and cracking are decreasing. However, even without these loud warning signs, it's important to dig down and identify any weak, sugary layers in the snowpack lingering below last week's storm snow. In areas where you find this weak snowpack structure, it is important to continue to make conservative terrain choices and use lower angle routes. We suspect areas near Mission Ridge and Blewett Pass have elevated danger associated with this problem. 

    While these layers may be beginning to heal, it is a slow process, and there is still the possibility of triggering a large and dangerous avalanche that runs at or near the ground. Northern aspects above 5000ft, particularly locations where the wind has drifted snow, are the most likely places to trigger these avalanches.

    (2/9/2021)

    Example of a persistent slab avalanche from 2021

    Photo: Matt Primomo

Avalanche Discussion

While access to higher elevations has improved significantly, it still requires lengthy approaches with many trees, shrubs, and stumps to avoid. Therefore, we are just beginning to understand the distribution and reactivity of these weak layers surrounding the 11/22 and 11/25 crusts throughout the zone, and we still have quite a lot of uncertainty. Evidence continues to roll in as avalanche professionals, and winter recreationists report finding this snowpack structure in many locations. However, some areas don't have enough snow overlaying this weak layer to produce avalanches. Therefore, conservative terrain choices are warranted until we gain more information. We have yet to put this layer to the test with another big storm, but snow is in the forecast, and the next storm event may give us additional information on how sensitive this layer is to triggering. 

If you are out and about in the mountains, you can help us by submitting an observation. 

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