Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

You can trigger dangerous avalanches from far away or in overhead terrain, especially where the wind drifts new snow. Watch and listen for signs of the danger including recent avalanches, loud collapsing noises, blowing snow, and snowpack tests that fail suddenly. Keep your distance and stay out from under large, steep slopes and places where avalanches could start, run, or stop.

Problemi valanghivi

  • Persistent Slabs

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

    You can trigger dangerous persistent slab avalanches on slopes 35 degrees and steeper. You may be able to trigger these avalanches from far away or from overhead slopes. Avoid being on or under suspect slopes, especially where you see fresh drifts. Leeward slopes at upper elevations where the wind deposits snow could be the most dangerous. Put a large buffer of terrain between where you travel and large start zones. Minimize your exposure to large avalanche paths and look for safe locations to stop or regroup.

    "Red flag" signs of the danger include whumphing collapses, cracks shooting through the snow, and tests that propagate or fail suddenly. The late-January weak layer can be found 1.5-2 feet below the surface and is a combination of weak, sugar-like facets and crusts. You may find the weakest snow sandwiched between two crusts. At mid-elevations, about 5,300-5,600ft, you can find buried surface hoar at this interface. We have good information about the problem near Washington Pass and Hart's Pass. We believe that the problem exists elsewhere in the zone, though we have less information about the nature of it there. 

    (2/1/2022)

    A similar snowpack structure and avalanche concerns exists in the Stevens Pass zone: Very long shooting crack in a wind drifted slope on a north aspect at 4,000ft near Henry Creek. The slab failed in weak, faceted grains above a stout crust. The crack ran about 100ft long.

    Photo: Matt Primomo

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Light snow accumulation and moderate to strong west and northwest winds will form shallow slabs at upper elevations. While you can keep from triggering these small avalanches by steering around the drifts, the persistent slab avalanches are much more difficult to avoid. Consider that you could also trigger these more deadly avalanches on most slopes where you see fresh wind loading. This could be enough to overload deeper weak layers. To stay safe, you will need to avoid both the wind slab and persistent slab avalanches.

    (1/9/2022)

    An example of wind transport and a wind slab avalanche from early January. West Rib of Silverstar. NW, 7,300ft

    Photo: Will Govus

Avalanche Discussion

Since earlier in the week, observers have reported numerous signs of instability, tests showing the potential for triggering avalanches, and now a couple of triggered avalanches on the late January facet/crust layer. Plenty of warning signs exist to show that we're dealing with dangerous avalanche conditions.

On Friday, observers reported remotely triggering a slab avalanche (size R4-D1.5) from approximately 600ft away on an east aspect near treeline in the Hart's Pass areas. This avalanche triggered another (sympathetic) small slab avalanche. Similarly, on Thursday, observers noted many whumphing collapses in Cutthroat, Wilow Creek, and West Fork of Cedar Creek. Professionals found sudden collapse test results and propagating extended column tests on a north aspect at 6,800ft. Another observer, on Kangaroo Ridge, also reported collapses in mid-elevation terrain and sudden collapse test results at 6,600ft, SW. The late January crust/facet weak layer has been responsible for these avalanches and signs of instability. Below treeline, specifically in the 5,300-5600' range in the Washington Pass area,  large surface hoar was widely observed at the same interface.

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