Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Snowfall will diminish on Tuesday but leave us with danger from slab avalanches at all elevations. Identify and avoid steep terrain with recent wind loading to reduce the risk of triggering an avalanche. Don't ignore obvious signs of instability like recent avalanches, shooting cracks, or whumping.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Wind slab avalanches were triggered in near and above treeline terrain on Monday in neighboring zones. They occurred on steep, unsupported terrain features. Small avalanches were observed to have released in a layer of colder, lighter snow about 10” down created by a quick drop in temperatures and a period of less wind on Sunday evening. A larger, remotely triggered avalanche on Shuksan Arm failed at or near the old surface crust buried by new snow on Sunday (photo).

    The wind slab distribution pattern is highly variable with big changes in slab depth over short distances. You can visually identify areas of wind loading by looking for pillowy drifts, cornices, and scoured snow surfaces. Dig down or use the handle of a ski pole to track the depth of new wind slabs over the old surface crust. Use simple tests like test slopes and hand shears to gather information as you gain elevation. Choose lower angle, planar slopes over unsupported, convex features to reduce the risk of triggering an avalanche in wind loaded terrain.

    (1/31/2022)

    Large, remotely triggered wind slab avalanche on Shuksan Arm in West North - N aspect @ ~5400'. The rain affected, old surface crust is visible at the bed surface.

    Photo: Liza Kimberly

  • Storm Slabs

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

    With a load of new snow from Monday’s storm, natural avalanches, signs of instability like whumphing, and unstable snowpack test results were noted in neighboring Stevens Pass. In addition to the usual instability that comes with new snow, variable old snow surfaces of slick crust, facets, or surface hoar are the likely culprits behind instability observed to the east. While these issues are not likely widespread across West Central, keep them in mind on Tuesday and use extra caution if traveling in areas south of the Mountain Loop.

    Test slopes, hand pits, and other snowpack tests will provide useful information, but the bond of new storm slabs to the old surface could be very different a short distance away. Reduce uncertainty by choosing lower angle, simpler terrain with less exposure to avalanches will the snowpack adjusts the new load.

    (1/31/2022)

    Small fracture on a NW aspect at 4,000ft in Stevens Pass. This failed on very weak faceted grains within a crust/facet sandwich. Small whumphing was also observed on nearby slopes.

    Photo: Matt Primomo

Avalanche Discussion

Precipitation totals from the last storm ranged from 1" to 2" across West Central with rain changing to snow at all elevations by Monday morning. The heaviest snowfall was associated with a Puget Sound Convergence Zone that centered on areas south of the Mountain Loop. New snow depths of 1' were observed in West North with up to 2' in wind loaded locations. Winds were strong during most of the storm with a lull when snow levels dropped.  Another period of strong winds formed additional wind slabs Monday morning.

In most areas of West Central warm conditions at the outset of the storm likely had a positive effect on the bond of new snow and wind slab layers. Snowpack observations in other zones found wet snow made for a good bond to the wide variety of old snow surfaces. Wind slab avalanches at this elevation were shallow and released within the layers of new snow. It is a different story moving into alpine terrain as colder snow may have preserved weak snow surfaces and provided the setup for surprising avalanches like the one that occurred on Shuksan Arm on Monday.

Use extra caution and go with a conservative terrain mindset moving into higher elevations.  Though no natural avalanches were observed above treeline, a large, remotely triggered avalanche is a telling sign there could be a major difference in snow stability with a small gain in elevation.

Regions covered