Boletín de aludes

East Slopes North

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 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Significant recent snow and wind have left heightened avalanche danger on slopes 35 degrees and steeper. You can trigger loose avalanches at lower elevations and drifted wind slab avalanches at upper elevations. Deeply buried weak layers of snow leave a chance for triggering surprising and very large avalanches, especially in the far eastern and western parts of the zone.

Problemas de aludes

  • Loose Dry

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

    On wind-sheltered slopes, the snow surface is light and uncohesive. You can trigger loose avalanches on slopes near to 40 degrees. While these avalanches can be easy to predict, they can be dangerous if you get caught off guard. Use caution around terrain traps like rocks, cliffs, and gullies where loose avalanches could bury you or cause injury. While traveling on steeper slopes, be aware of any snow that begins to slide around or behind you. Slow down or move to the side so these avalanches don't carry you down-slope. Make sure to stop and regroup well off to the side and in safer terrain if others are traveling on overhead slopes.

    (2/9/2021) An example of dry loose avalanches on Snoqualmie Pass. Don't get knocked off your feet or pushed into a terrain trap by one of these when there is so much snow. [Photo: Zack Wentz]

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    You may still be able to trigger wide and surprising avalanches on older, faceted grains or buried surface hoar in both the far western and eastern reaches of the zone. Audible whumphing collapses, cracks shooting through the snow, and widely propagating avalanches are all warning signs. You could trigger slides on convex rolls and unsupported features. While the likelihood of these avalanches is dropping, the consequences remain high. If in doubt, opt for lower angle terrain and consider sticking to slopes less than 35 degrees.

    Observers are still finding a layer of buried surface hoar and small facets in the top 3 feet of the snowpack near Washington Pass. East of Washington Pass, the most recent known persistent slab avalanche was on February 3rd. Observers suspect a very large avalanche involved persistent weak layers near Rainy Pass on the 8th (see discussion). Far east and just west of Washington Pass, you may be able to trigger avalanches on older, weak facets above or between crusts from mid-January. This weak layer is also about 3 feet below the surface in these areas.

    (2/9/2021) A very large avalanche at 6,400ft, ENE near Rainy Pass. This avalanche may have run on 8th on a deeply buried persistent weak layer. You can see many snowmobile tracks in the area. Photo: Jeff Ward

  • Wind Slabs

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

    As recently as Saturday night, strong westerly winds formed slabs on leeward slopes. Wind slabs will be bigger and easier to trigger above treeline. Feel for wind stiffened or hollow sounding snow as you enter open areas and change aspects. Be especially careful of cross loaded gully features and cornices. Watch for shooting cracks or whumphing collapses as a clear sign of instability.  Wind slabs could also step down to other weak snow layers in the top 2ft of the snowpack.

    (2/6/2021) A skier intentionally triggered a small wind slab avalanche on a SW aspect at 74000ft near Washington Pass on Saturday.

Avalanche Discussion

An avalanche fatality occurred on February 8th in the Knox Creek drainage in the neighboring East Central zone. Our condolences go to the friends and families of those involved. Similar avalanche conditions may exist near the eastern and western boundaries of this zone.

On Tuesday, an observer on Whistler Mountain reported sudden and propagating test results on a west aspect at 6,000ft as well as on a NW aspect at 6,600ft. The weak layer was facets on a crust from mid-January (1/14) down about 90cm at 6,600ft. This weak layer appears to be more shallowly buried and more problematic west of Washington Pass, as well as in the far eastern mountains of the Twisp River and Chewuch drainages. A very large avalanche was reported at 6,400ft, ENE near Rainy Pass. This avalanche may have run on the 8th, perhaps on the same (1/14) persistent weak layer as observed on Whistler Mtn.

On Monday, observers near the hairpin on Washington Pass reported an additional 5 inches of snow overnight with over 2 feet of storm snow since the 5th and wind transport at ridgetops. Observers on Delancey Ridge reported about half as much storm snow and still found tests indicating propagation on the Jan 30th interface of facets and surface hoar at 6050ft on a southeast aspect. On Sunday, observers dug a profile on a SW aspect at 7,200ft and found reactive storm interfaces down 1 foot and a layer of rounding facets (likely Jan 30th) about 2 feet below the surface. 

On Saturday, a skier intentionally triggered a small wind slab on a cross-loaded southwest slope at 7400ft near Washington Pass. On Friday, a large ski triggered avalanche was reported near treeline along with several small wind slabs in steep terrain below cliff features in Cutthroat drainage. A week ago, on February 3rd, we believe that a significant portion of Portley Bowl avalanched naturally following a ski triggered slab on a smaller part of the bowl on the 2nd. Another skier had a close call, also on February 2nd, near an area often thought of as 'safe' ski terrain. We suspect buried surface hoar as the culprit for these two avalanches last week.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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