Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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In sintesi

On Friday, you can trigger slab avalanches near and above treeline where the wind deposited stiffer slabs of snow over the past three days. Watch whumphing collapses and cracks shooting through the snow and stay off of slopes over 35 degrees with deeper pillows and drifts. You may be able to trigger large avalanches on steep slopes in the eastern mountains if you see these warning signs.

Problemi valanghivi

  • Wind Slabs

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

    To stay safe, steer around fresh pillows of snow or stick to windward terrain and slopes less than 35 degrees. Avoid areas with terrain traps like rocks and cliffs where avalanches could have dangerous consequences. Pay attention to localized wind drifting direction to clue you into where you may be able to trigger an avalanche. Winds out of both the northeast and west drifted slabs since Tuesday.  In isolated high-elevation terrain, the new load of wind-deposited snow could stress more deeply buried weak layers. See more below.

    (12/14/2022)

    Blowing snow from northeast winds in the Blue Lake area.

    Photo: Willie Webster

  • Persistent Slabs

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

    If you're traveling near or east of Mazama, consider the potential for triggering these dangerous avalanches. There are ample signs of instability from the eastern mountains and lowland foothills of the Methow Valley. Stick to lower-angled slopes if you see cracks shooting through the snow, experience loud collapses, or find strong over weak layers that produce sudden or propagating test results. You'll find a weak layer of facets in the lower half to a third of the snowpack and often under one or two crusts. 

    Triggering an avalanche on older weak layers near Washington Pass and the Cascade crest is unlikely but not out of the question. Generally, observers have found no older weak layers of concern in these areas. A few observations during past loading events indicate persistent slab avalanches could be possible near valley bottoms and in isolated areas above 7,000ft, where the mid-November facets are still weak. See Discussion for details. If you hit the wrong spot, you could trigger a dangerous avalanche.  

    (12/14/2022)

    Large avalanche crown running across the top of an east facing slope in Finley Canyon, southeast of Twisp.

    Photo: Public Obs

Avalanche Discussion

Since Tuesday, observers reported plumes of blowing snow and cracking in freshly drifted wind slabs above treeline. Winds should be light on Friday.

 On Wednesday, an observer in Finley Canyon reported a large natural avalanche that propagated over 500ft wide on an east aspect and likely involved the mid-November facets. On Monday, observer, Drew Lovell, reported on conditions both north and south of Washington Pass. Observers have found a layer of surface hoar, buried December 8th, about a foot below the snow surface. The layer has generally not been a problem for avalanches in this zone. On Sunday, an observer on Delancey Ridge reported propagating test results on the mid-November facets, 50cm below the surface.

At the tail end of last weekend's storm, observers reported two notably deep avalanches on Big Kangaroo Peak, WNW, 7,700ft. While we can't confirm this, there's suspicion that they may have run on older weak layers. On December 3rd, I experienced a large collapse on an adjacent slope in a shallow area (~100cm) of older drifted slabs resting on the mid-November facets. While notable, these observations are outliers to most other observations from mid to upper elevations near the Cascade crest that report the layer as unreactive or less concerning. 

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