Bulletin d’avalanche

Stevens Pass

Dec 20 – 21, 2018Northwest Avalanche Center
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Archivé · expiré 8 years ago

Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Points saillants

You can trigger avalanches at upper elevations due to drifting snow and strong winds. Minimize your exposure to large steep slopes and avalanche paths. If you experience collapsing, cracking in the snow, or see recent avalanches, avoid open slopes 35 degrees or steeper.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1

    Steer around wind loaded features on slopes steeper than 35 degrees. Use caution just below ridges and avoid slopes where the snow is thickly pillowed and deep.

    Avalanches will be easier to trigger as you climb higher in the mountains. Strong wind from the past 3 days has formed slabs near and above treeline. You can trigger these avalanches where you see fresh wind features. Older wind slabs will be harder to see, as they’ve been covered by recent snow. Probing for stiff snow just below the surface can help you identify these areas.

  • Deep Persistent Slabs

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

    Persistent slabs are difficult to predict and often break much larger and wider than you expect. Minimize your exposure to avalanche terrain:

    -Limit the amount of time you spend near slopes 35 degrees and steeper.

    -Put an extra buffer of terrain between where you travel and where avalanches could start.

    -Stay well out from under large avalanche paths and identify safer areas to stop and regroup.

    You are most likely to trigger these avalanches in the eastern portion of the zone. At the top of Stevens Pass, these avalanches are now difficult, but not impossible, to trigger. Persistent Slab avalanches due to old weak snow that formed in early December. If you dig in the snow, you will find a layer of sugar-like, facets and old surface hoar buried 5-6 feet below the surface.

Snowpack Discussion

Regional Synopsis: December 19, 2018

Why has the avalanche danger been so high for so long? Two reasons: A very active and wet weather pattern combined with a widespread persistent weak layer.

For perspective, the approximate snow totals from 12/9-12/19 are:

  • Mt Baker: 102”

  • Washington Pass: 55”

  • Stevens Pass: 76” mid-mountain

  • Snoqualmie Pass: 68” mid-mountain

  • Crystal Mountain 70” Green Valley

  • Paradise: 78”

  • Mt Hood Meadows: 44” mid-mountain

  • Olympics: 48”

In many areas, a layer of buried surface hoar and/or weak sugary facets was buried on December 9th. This layer has been the cause of numerous natural, explosive, and skier triggered avalanches. As this layer gets deeper it gets harder to assess. In short, the scenario is tricky and getting more dangerous by the day.

Higher snowfall totals along the Hwy 542 corridor/Mt Baker area have driven several avalanche cycles during this period. Loading from recent storms has been more incremental to the east and south of the Mt. Baker area, so we have not yet experienced a widespread cycle in other areas.

When will we reach the breaking point? It’s hard to say. What we do know is we have a deep weak layer, reports of very large explosives triggered slides at Mission Ridge and Crystal Mountain, and more storms on the way.

Be patient and continue to stick to lower angle slopes with nothing above you.  This is a good time to avoid areas where avalanches can start, run, and stop.

We’d like to thank all of you who have sent NWAC your observations. If you are out in the mountains, let us know what you see.

Régions couvertes