Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You can still trigger slab avalanches that formed with recent wind and snow. Use extra caution on slopes over 35 degrees where the wind has drifted snow into deeper slabs. If the new snow slides easily in tests or if you see recent avalanches at any elevation, stick to lower-angle slopes.

 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    The most dangerous areas will be leeward sides of ridges and wind-exposed features above treeline that are 35 degrees and steeper. Avalanches in these areas could be big enough to bury or kill you. Use your probe to feel for stiffer, deeper drifts to indicate wind-loaded slopes. You can avoid triggering these avalanches by sticking to wind-sheltered or windward terrain, or traveling on slopes less than 35 degrees.  If you see recent avalanches or cracks shooting through the snow, seek these areas of safer terrain.

    (1/17/2023)

    An example of natural wind slab avalanches near the base of a cliff. 

    Photo: Katie Warren

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    You may still be able to trigger avalanches on wind-sheltered slopes over 35 degrees. Look for stiffer snow over softer snow as an indicator that you can trigger storm slab avalanches. Use smaller, low-consequence test slopes to check how easily the snow slides. You can make many quick, informal tests as you move through the terrain.  Look at the interface that was buried at the beginning of this storm, about 1.5-2 feet below the surface. If you find sudden or propagating test results on the older, weak snow, stick to lower-angled slopes.

    (1/9/2023)

    An example of a shallow storm slab beneath a rock outcrop.

    Photo: Willie Webster

Avalanche Discussion

Good visibility on Wednesday allowed observers to tally the impacts of storms since the 3rd. They reported a number of large to very large (up to size D3) avalanches throughout the Highway 20, Washington Pass area. Crowns were mostly near ridges or below cliff bands in wind-loaded terrain. Many of these appear to have run during a 24-hour period on February 7th.

On Wednesday, observers near Vasiliki Ridge reported over 7" of new snow in 24 hours and notable wind drifting above treeline. Observers in the Hairpin Valley found almost 2 feet of snow below treeline that fell since the 3rd. While the Feb 3rd interface has generally been well-bonded, observers have reported mixed results. On Wednesday, a triggered slide near the Lyal glacier stepped down to the new/old interface and broke into a large avalanche, 6,400ft, east aspect. On Sunday also near Rainy Lake, I found planar shear at the Feb 3rd interface at a profile site near treeline, though I couldn't produce similar results in a number of other quick tests near and below treeline.

There are a few layers that we've been tracking in the upper snowpack. The February 3rd interface, buried by the most recent storm and could harbor small near-surface facets. The Jan 5th surface hoar (about 2-2.5ft below the surface) had previously been widespread and problematic in snowpack tests. With time and rounding of the grains, this layer may be strengthening. At a profile on Sunday above Rainy Lake, test results indicated that the layer was not a problem for avalanches at that location. Elsewhere, especially in the eastern mountains, this layer could still be an issue if it gets stressed with the weight of enough new snow.

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