Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Continued snowfall accompanied by moderate winds should help create dangerous avalanche conditions on Sunday. You are more likely to trigger an avalanche in wind-loaded terrain on steep slopes over 35 degrees. Look for visual clues such as textured surfaces or smooth pillow-like piles of snow to help you identify these areas to avoid.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Winds around the pass should remain strong enough to blow around freshly fallen snow into unstable Wind Slabs on Sunday. Look for these slabs to develop on the leeward side of ridgelines, on convex features, or near rocky terrain such as confined chutes or the base of cliffs. Slabs should be thicker and possibly more reactive as you ascend in elevation, but could develop even down in the trees. You can use visual clues such as textured surfaces, freshly built cornices, or actively blowing snow to help you find where Wind Slabs may have developed. Using small test slopes or upslopes tests are great ways to determine how the snow is reacting to your weight and if a slab is present. If you notice cracking of the surface or that the snow is firm and feels hollow, you should head for slopes under 35 degrees that are sheltered from the wind.

    (4/9/2022)

    Wind-loaded test slopes produced cracking and showed slab character on Kendall Peak on 4/9. A good indication that human trigger Wind Slabs were possible on larger slopes.

    Photo: Andy Harrington

Avalanche Discussion

The calendar tells us it’s April, but step outside at Snoqualmie Pass and you’ll quickly realize that winter weather has a strong grasp on our zone. Stormy conditions should persist throughout the weekend, with additional snowfall and gusty winds. On Saturday, NWAC forecasters on Kendall Peak observed plenty of signs of wind effect with textured surfaces, scoured areas, and fresh drifts. The recent storm snow was generally well bonded to the underlying 4/8 crust and in areas not affected by the wind, the snow lacked slab characteristics. Most of the storm snow contained graupel, which was a threat for Dry Loose avalanches on steeper slopes. The weather was all over the place, with periods of sunshine, heavy snow, and gusty winds, sometimes within only minutes of each other.

The amount of new snow received to this point is hard to pin down due to wind transport, but various reports found anywhere from 5-10” of new snow at mid to upper elevations over the 4/8 crust. On Sunday, this depth will only increase and the winds should again be strong enough to drift the low-density storm snow into thicker slabs. The storm may have its greatest impact in the morning hours before transitioning into a more showery pattern in the afternoon. As we incrementally increase the amount of storm snow, we should crest the threshold for larger and more dangerous avalanches. While Wind Slabs may be the most concerning problem you will need to manage, loose avalanche problems (both dry and wet) should have your attention as well. On Saturday, it only took a few sun breaks to warm up the snow at lower elevations and start to approach the threshold for pushable Wet Loose avalanches. This is common in the spring so be prepared to avoid steeper sunny slopes if the weather forecast busts and there are breaks in the clouds on Sunday. While we expect the majority of these loose avalanches to be small, don’t get swept off your feet in consequential terrain.

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