Bulletin d’avalanche

East Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions continue for Tuesday, as we are on the tail end of a significant avalanche cycle. Keep your distance from slopes steeper than 30 degrees especially near and above treeline. Stay out from under large, overhead avalanche paths.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    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 steeper than 30 degrees. Make sure you're not standing below or adjacent to steeper slopes. Use clues to stay out of avalanche paths, like trees stripped of uphill branches or openings in vegetation that run up slopes. Watch for obvious signs of instability like recent avalanches, whumphing collapses, or cracks shooting through the snow.

    (12/18/2020) Example of a widely propagating persistent slab that surprised experienced backcountry travelers in the Stevens Pass zone. The slide was triggered from below.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Watch for triggering avalanches in recent storm snow. Cold snow will fall with cooling temperatures on Monday night. Following travel advice for the Persistent Slab avalanches will keep you from triggering avalanches in the storm snow as well. At upper elevations, this new snow may be drifted and adding stress to the underlying weak layer. In addition, you may be able to trigger small avalanches on lower elevation slopes. At the lowest elevations, you may find heavy wet snow that has yet to freeze. 

Avalanche Discussion

By Tuesday morning 24 hour snow totals will approach 2 feet. This likely tipped the balance of the snowpack. The stormy conditions have limited observations but in adjacent zones, good evidence of a widespread avalanche cycle exists. On Monday, observers reported small natural avalanches in storm snow and large collapses above 6,000ft (likely involving buried facets). You can find a layer of weak facets about 3 feet below the snow surface that was buried in early December. This rests on a crust on many slopes which is especially thick below 5,500ft. Throughout the week, observers have reported numerous collapses, propagating test results, and even avalanches on this weak layer in the past week. On the 18th, observers reported triggering a size D1.5 avalanche in the Cuthroat drainage on a S aspect at 5,300ft.

Régions couvertes