Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

7a UPDATE: Avalanche Warning, 18" of snow overnight with 2" of water equivalent. Avoid traveling in avalanche all terrain. Ongoing snow and strong west wind will make it easy to trigger large and destructive avalanches that could break widely across slopes. Stay far away from and well out from under wind-loaded, open slopes that are steeper than 30 degrees.

Problèmes avalancheux

  • Persistent Slabs

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

    Persistent slab avalanches are difficult to manage and can catch even experienced travelers by surprise. Obvious signs of avalanche danger include cracks shooting through the snow, whumphing collapses, and recent avalanches. The best way to stay safe is to avoid open slopes steeper than 30 degrees and put a large buffer of terrain between where you travel and all avalanche paths. Make sure to regroup and stop only in truly safe terrain, well away from and out from under steeper slopes. You may be able to trigger these avalanches from a long distance away. Triggering avalanches is likely on recently wind loaded slopes, and they may be especially reactive on southerly slopes that are typically sun-exposed.

     About 2-3 feet below the snow surface, you can find a softer layer of snow above a crust formed in mid-January. On Friday, observers confirmed avalanches that broke widely and were remotely triggered on this layer. This snowpack structure can be found on most slopes, and there's uncertainty around how widespread these avalanches will be in the terrain. To be safe, approach any slope steeper than 30 degrees with extreme caution. When in doubt, avoid avalanche terrain.

    (2/6/2021) This slab was intentionally triggered by a small cornice drop on Saturday (2/6) in the Crystal backcountry. It propagated widely and is believed to have run on the Mid-January crust/facet combo. Similar avalanches have been reported from this zone. [E aspect, 6300'. Photo: Jeremy Allyn]

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2

    Watch for wind-stiffened snow, drifting, and actively blowing snow. Avoid leeward slopes where westerly wind has deposited thick slabs over the past 3 days. Avalanches will be bigger and easier to trigger above treeline. You may even be able to trigger wind slab avalanches in open terrain below treeline. Any slide could break into older weak layers of snow causing a very large and destructive persistent slab avalanche. Use caution near cornices and the edge of ridgelines. You may be able to trigger wind features and cornices very easily. 

    You can trigger both loose and slab avalanches in storm snow on wind-sheltered slopes. Fluctuating temperatures over the past couple of days may leave strong over weak layering in the upper snowpack. Whether you're in sheltered or wind-exposed terrain, you can use small, inconsequential slopes to check if the storm snow slides or cracks easily.

    Example storm slab on a small test slope.

Avalanche Discussion

Uncertainty exists around avalanche danger and precipitation for Sunday. Poor visibility and dangerous conditions have limited observation for the past couple of days. The peak of avalanche activity likely will have occurred Saturday night, but it's difficult to be certain about the exact conditions on Sunday. With this in mind, use extra caution and be certain of your ability to avoid any and all avalanche terrain, if necessary.

On Friday, I observed a very large and widely propagating persistent slab avalanche in Highlands Bowl (SE at 5,600ft) outside of the boundary of Stevens Pass resort. Professional guides reported huge collapses (whumphs) below Skyline Lake. Ski Patrol at the pass remotely triggered 2ft deep avalanches while skinning on a ridgeline. These were on northeast aspects at 5,800ft and ran on the mid-January crust facet layer. WSDOT triggered large avalanches in both new snow, and older snow early in the morning as well. One was a D3 avalanche (big enough to break trees) and ran on the same crust. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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