Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Heavy snow, wind, and maybe even rain will make for very dangerous avalanche conditions. If you choose to go in the mountains, be confident in your ability to avoid avalanche terrain and stay out from under areas where avalanches could come down from above. The danger may be highest near the Cascade crest and anywhere that receives significant heavy snow or rain.

Problemi valanghivi

  • Storm Slabs

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

    Make sure to stay well away from tracks and runouts of pathes, where avalanche could come from above.  Pick truly safe terrain to stop and regroup in. By the end of the day, you may see natural avalanches on a variety of slopes. Avalanches could be large if they break into snow that fell since the 18th. If you signs of instability, like cracks shooting through the snow or whumphing collpases, avoid avalanche terrain. When in doubt, stick to slopes under 30 degrees. 

    Warm, heavy snow will slide easily on the weak upper snowpack. Make your own observatios to asess the hazard and be ready to choose safer terrain. The cold temperatures have kept observations limited and diminished our confidence in the forecast.

    (2/5/2022)

    An example of a skier triggered avalanche near Maple Pass last season.

    Photo: NWAC public obs

  • Persistent Slabs

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

     The new snow is making it easier to trigger these dangerous avalanches. If you see cracks shooting through the snow, experience loud collapses, or find strong over weak layers that produce sudden or propagating test results, stick to lower-angled slopes. These avalanches are most likely near and east of Mazama. With the ongoing loading of new snow, keep an eye out for signs of instability. You'll find a weak layer of facets in the lower half to third of the snowpack and often under one or two crusts. 

    Triggering persistent slab avalanches near Washington Pass and the Cascade crest isn't out of the question. Some recent avalanches were suspected to have involved the December 8th surface hoar, about 2 feet below the surface. Older observations indicate that persistent slab avalanches on weak layers in the lower snowpack could be possible near valley bottoms and in isolated areas above 7,000ft, where the mid-November facets are still weak.

    (12/18/2022)

    Very small persistent slab avalanches released on unsupported features when a skier approached from above.  Silverstar - Below Treeline

    Photo: Katie Warren

Avalanche Discussion

The incoming storm will bring warmer temperatures as we enter the weekend. It remains to be seen just how warm it will get and if we'll receive any rain. Small amounts of rain could reach Rainy Pass or Washington Pass by the end of Saturday. There may also be light rain near and down valley of Twisp. Stay tuned for this dynamic storm as it's been challenging to forecast.

On Friday, Observers near the Silverstar drainage reported up to 4" of new "cake frosting" on the surface. The mountains close to the Cascade crest picked up close to 20" of snow through the 20th. On Tuesday, observers near Cutthroat Lake reported two larger natural slab avalanches likely due to new snow and wind loading. At least one of these may have run on older weak layers around 7,200ft, ENE in Swamp Creek (see photo below).  Observers continue to report lots of collapsing and cracks shooting through the snow in the eastern foothills. On the 18th, an observer triggered a small avalanche on an unsupported northerly feature below treeline in the Silverstar drainage. The slide ran on the mid-November facets. 

The December 18th interface holds weak grains of small facets, surface hoar, and crusts on southerly aspects. You may be able to find buried surface hoar from December 8th about 2 feet below the snow surface.

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