Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

Dangerous avalanche conditions continue after a widespread cycle of very large avalanches. Above 5600ft, it may still be possible to trigger a very large and deadly avalanche. The best way to deal with the uncertainty of triggering avalanches on deeply buried weak layers is to stick to slopes less than 35 degrees and avoid lingering below avalanche terrain.

Problemi valanghivi

  • Wind Slabs

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

    Watch for triggering avalanches in recently drifted snow. Following travel advice for the Persistent Slab avalanches will keep you from triggering avalanches in recent storm snow as well. Avoid leeward slopes where the snow looks thick and pillowed. look for wind features in the snow and areas of deeper snow adjacent to shallower areas. Feel for stiffer snow under your skis or feet. At upper elevations, this new snow may have added stress to the underlying weak layer. 

    (12/22/2020) Avalanche workers intentionally triggered a fresh wind slab avalanche on an ENE aspect at 5,000ft near Stevens Pass. The crown was 200ft wide and 18-24" deep.

  • Persistent Slabs

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

    Persistent slab avalanches could be very large and could easily bury or kill you. These dangerous and surprising avalanches can catch even the most experienced backcountry travelers. The most dangerous slopes will be at higher elevations, where southwest wind formed drifts and where the snow stayed mostly dry. You may be able to trigger them from long distances away. They may come down from slopes above you. Keep your distance from any slope 35 degrees and steeper. Make sure you're not standing below or adjacent to steeper slopes. While it's slowly becoming harder to trigger these avalanches, we still have a lot of uncertainty. It's a good idea to give the weak layer more time before venturing into avalanche terrain.

    You can find a thin weak layer of small facets (and in places surface hoar) buried about 2-4 feet below the surface. Near the top of Washington Pass, this weak layer will be sitting on an icy crust. Further east in the zone, the crust becomes thin and is breaking down into a mix of melt forms and weak grains. On Wednesday, observers reported whumpfing collapses and tests that indicated the potential to trigger avalanches on this weak layer, especially above 5,600ft. At lower elevations, there's less concern for triggering persistent slab avalanches. However, it's possible that you could trigger an avalanche that starts in terrain well above where you travel.  

    (12/22/2020) Many avalanche crowns at 7400-7800ft, SE-SW in Pine creek. A widespread avalanche cycle occurred on Dec 21st on Washington Pass.

Avalanche Discussion

Heavy snow and wind on the 21st tipped the balance of the snowpack. We've received good evidence of a widespread avalanche cycle in the Highway 20 area. An observer reported a handful of large avalanches near Silverstar and Varden creek drainages. This includes slab avalanches on a northeast aspect at 6,400ft just west of Silverstar Creek, a west aspect at 6,800ft on Gardner Mountain, and a northeast aspect at 8,000ft on Silverstar Mountain. All were size D2. Many avalanches were visible on southeast through southwest aspects of Delancey Ridge and Pine Creek above 7000ft. Some crowns propagated hundreds of feet with debris running over 2000ft into the valley below.

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