Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Wed
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2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

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 eastern part of the zone.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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.

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1

    On many 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.

  • Persistent Slabs

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

    You may still be able to trigger wide and surprising avalanches on older, faceted grains or buried surface hoar 2-3ft below the surface. 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 about 2-3 feet below the surface near Washington Pass and especially in the Cutthroat drainage. The most recent avalanche suspected on this layer was on the 3rd. Test results and a lack of recent signs of instability indicate that avalanches are becoming harder to trigger. Further east, 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 the eastern mountains of the Twisp and Chewuch drainages.

    (2/3/2021) A ski triggered avalanche was reported in Portley Bowl on 2/2. The next day an observer took the bottom photograph at 10:50AM. The majority of the rest of the slopes in the bowl had avalanched, with no ski tracks observed in or out of the slides. These may have been solar triggered, and suspected to have failed on a buried surface hoar layer from 1/30.

Avalanche Discussion

Preliminary avalanche incident information Monday February 8th, 2021: Two snow bike riders were caught and buried by a very large avalanche in the mountains west of Salmon la Sac Sno-Park along Cle Elum Lake. One snow biker was partially buried and was able to dig himself out. The other rider was fully buried and killed by the avalanche. The avalanche occurred on a north aspect at 4400 ft in the Knox Creek drainage. This terrain lies in NWAC’s East Central forecast zone. Avalanche classification: HS-AV-R3-D3-O. 

All of us at NWAC want to extend our condolences to family, friends and the local community following this tragic event.  

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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. Last Wednesday, we believe that a significant portion of Portley Bowl avalanched naturally following a ski triggered slab on a smaller part of the bowl on Tuesday. Another skier had a close call on Tuesday 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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