Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Tue
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 with heavy snow and strong wind near and above treeline.  You can trigger dangerous persistent slab avalanches on slopes steeper than 30 degrees at upper elevations. Rain will keep wet avalanches possible at lower elevations.

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 best way to stay safe is to avoid where these avalanches exist. It's not realistic to manage the risk of an avalanche once you trigger it.

    The highest elevation, leeward slopes will be the most dangerous.  Above treeline, snow will stay dry and southwest wind will drift snow. You can trigger these avalanches from long distances away. They may even run naturally and may come down from slopes above you. Keep your distance from slopes 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) Part of a remotely triggered persistent slab avalanche (D2) that was ~500ft wide and 15"-20" deep. Lanham creek, 5800ft, NE.

  • Loose Wet

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

    Loose wet avalanches could be triggered or run spontaneously during the day. These could be large, and may gouge down to the early December crust. You will probably see evidence of recent activity if you look around at steep hillsides, as many naturals may run overnight Saturday into Sunday morning. Signs of loose wet instability are rollerballs, and wet sticky snow that entrains as it moves downhill. The best way to manage large loose wet avalanches is to avoid being underneath very steep slopes, even in forested terrain if the trees are spaced out. 

    Example of a large loose wet avalanche.

Avalanche Discussion

On Saturday and Sunday observers noted a cycle of natural slab avalanches in the zone up to D2.5 (big enough to injure, bury or kill a person). Some of these had widely propagating crowns, and are suspected to have run on facets above the prominent 12/9 crust. On Sunday, observers reported a slab avalanche on Lichtenberg Mtn, SE, 5600ft with a crown depth estimated at 1-2 meters (up to 6 feet). On Saturday, observers reported a widespread cycle of slab avalanches mostly on northerly aspects above 5,500ft. On the 17th a party remotely triggered a large avalanche on a northeast aspect at 5800ft above Lanham Lake with a crown about 500ft wide.

Régions couvertes