Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

This weather pattern isn't done with us yet, and more snow with increasing winds on Thursday will keep the avalanche danger elevated. You could easily trigger large avalanches, particularly in wind-affected areas. Avoid steep terrain, particularly slopes below ridges and the base of cliffs, with deep slabs of wind-drifted snow. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    With winds up to 20-30mph on Thursday, fresh wind slabs may be the more obvious avalanche problem, but we can't rule out storm slab avalanches in steep, sheltered terrain. The most potential for sensitive, very large avalanches is on lee slopes at mid and upper elevations. But don't get caught off guard by steep features and slopes in sheltered terrain where you can trigger storm slabs. Choose low-angle slopes to avoid triggering a dangerous avalanche. Alpental Ski Patrol triggered a very large avalanche that ran on a melt-freeze crust on Wednesday. While explosives triggered this avalanche, similar avalanches with smaller triggers have occurred in other zones, and some ran naturally. These avalanches would be many feet deep and could wrap around terrain features.

    (12/20/2022)

    Example:  You could still trigger storm and wind slabs of all shapes and sizes on Thursday, including deep ones involving all the recent snow. 

    Photo: WSDOT Avalanche Team

Avalanche Discussion

Another 6-8 inches of snow is in the forecast for Thursday, and wind speeds will pick up throughout the day. Observers at lower elevations reported 20-30cm of snow over a crust formed during a brief warm-up on Monday night. Since the storm began on Monday afternoon, over 4" of water, 3-4ft of snow, have fallen in the Snoqualmie Pass area. The backcountry landscape looks significantly different than just a few days ago. Both the snowpack and our information on conditions need time to adjust to this new landscape. With this increased uncertainty, avoid stepping out into bigger terrain too quickly. Enjoy the significantly better snow conditions on lower-angle slopes as you gather more information on the state of the snowpack. 

We still have uncertainty regarding several weak layers in the upper snowpack (Jan 4, Jan 2, 12/25, and Solstice Crust) that contain crust/facet combinations. However, the very large (D3) avalanche triggered by Alpental Ski Patrol during avalanche control is critical information that these deeply buried layers may still be active. Before this storm, snowpack test results were variable, but these layers failed and propagated in some. In other zones, these layers have proven to be an ongoing problem. This is enough evidence to suggest any one of these weak layers could produce very large avalanches. Until we can gather more information on their potential reactivity, extra caution and wide margins of safety are warranted. 

Regioni coperte