Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

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

Avalanches will be easiest to trigger and most dangerous on steep slopes where the wind drifts snow. A major westerly wind event will keep forming  stiff slabs that could overload the weak snowpack, resulting in large, widely breaking avalanches. Stay off and out from under wind-loaded slopes at middle and upper elevations. 

Avalanche problems

  • Persistent Slabs

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

    We expect especially dangerous conditions at middle- and upper-elevation leeward slopes. In wind-loaded areas, avalanches may break widely across terrain features or be triggered remotely. Look for actively blowing snow and thick pillow-like drifts to point out the danger. Keep your distance from these slopes and stay well out from under them. Treat this snowpack as guilty until we can rule out specific areas. Seek out low-angle terrain that's protected from the wind. 

    Long shooting cracks, whumping collapses, or natural avalanches are key indicators of dangerous avalanche conditions. Since the weekend, most observers have reported collapses at lower and middle elevations, including on wind-sheltered slopes. At low elevations, these avalanches may act more like your average storm slab, but the instability is already lasting longer than normal. Weak layers adjacent to crusts are widespread on a variety of slopes, just 1-1.5 feet deep, and have been the source of multiple avalanches in the past week. 

Avalanche Discussion

Ongoing westerly winds will dominate the weather at least through Friday. This wind event is so significant that the drifted slabs are adding stress to the weak, underlying snowpack. A major warm-up is coming over the weekend, which will maintain dangerous conditions.

On the 26th, Stevens Pass patrol reported natural and triggered avalanches in wind-loaded terrain on east and leeward sides of ridges. One person was caught and uninjured in a sized D1.5 slab avalanche. Westerly winds have been strong, driving intense wind loading. On the 23rd, 7-10" of snow accumulated and stressed weak faceted snow and buried surface hoar. Observers reported some natural and many human and explosive-triggered avalanches running to the uppermost (2/8) crust. Whumpfing collapses have been widespread. Moderate to strong winds drifted snow on the 25th, though we don't have much information on the impacts yet. In the Lichtenberg area on Tuesday, an NWAC forecaster also reported moist snow below 4500ft and a thin crust that formed and was quickly buried by fresh snow. Consistent with previous observations, snowpack tests have produced mixed results, but the snowpack is very weak. The uncertainty is a good reason to minimize exposure to avalanche terrain and enjoy the return to winter on lower-angle slopes. 

A layer of facets, including the 2/13 surface hoar, is now buried 8-15" deep, and the 2/8 crust is down 10-20". Avalanche activity from this week suggests that southern aspects may be more reactive than northern aspects. But the weak structure exists on all aspects around the compass.  In most areas, these avalanches have been small. While some have been triggered remotely, we have no reports of widely propagating slides in this zone. About 12-16" below the surface, you'll find a more stout, thicker crust with additional weak snow adjacent to it. Upper elevations will likely have a greater separation between crusts, with potentially more weak layers. We have limited information from upper elevations, above 6,000ft. If you travel there, we'd love to have your observations!

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