Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions remain on the heels of a very strong and windy storm. You can trigger large avalanches in wind-drifted areas at mid and upper elevations. Prepare for very cold temperatures and deep snow hazards.

Problèmes avalancheux

  • Wind Slabs

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

    Use extra caution on all slopes steeper than 35 degrees. If you see cracks shooting through the snow, stick to lower-angle terrain. Use small test slopes to see if the snow slides easily. As winds should taper off by Wednesday, you'll need to look for clues like sculpted features and stiff surfaces to indicate previous wind-loading directions.

    On Tuesday and Tuesday night, strong southwest through northwest winds formed slabs at all elevations. The most dangerous areas will be near and above treeline on leeward slopes below ridges. You can trigger avalanches big enough to kill you at these upper elevations. Below treeline, avalanches won't be as big (but still dangerous) and they'll come in a wider variety of flavors. Expect wind slabs in open, wind-exposed terrain. In sheltered areas, you may be able to trigger storm slab or loose avalanches at an interface from Tuesday.

Avalanche Discussion

On Tuesday, observers reported easily triggering many soft slab avalanches in the upper portion of the new snow where a slightly heavier layer rested on very cold, dry snow. One observer was knocked over, partially buried, but uninjured. We received reports of widespread cracking even in wind-sheltered terrain. Westerly winds were strong enough to form drifts even below treeline.

Temperatures are extremely cold. Bring plenty of warm layers and monitor exposed skin for cold injuries. With all the new snow, falling in tree-wells and holes around creeks and boulders can be dangerous. Keep your partners in sight and within earshot.

As of Tuesday night, Stevens Pass picked up over 1.3" of water equivalent in the form of light, dry snow. Temperatures stayed cold throughout the mountain, though warmer air aloft created extreme temperature inversions, of 20 degrees Fahrenheit between 4,000-5,000 feet. This fell on another foot of very light snow that accumulated on Monday.

The December 18th interface holds weak grains of small facets, surface hoar, and crusts on southerly aspects. I found easy, sudden shears in snowpack tests on this interface on Monday. You may still be able to trigger avalanches on this interface 2-2.5 feet below the surface. The snowpack harbors weak layers, buried in late November, near the bottom of the snowpack. While they haven't been involved in avalanches in over a month, a very big storm could activate them.

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