Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Small natural storm slab avalanches were observed on Sunday and more snow is on the way. Even though this may not seem like a big storm by Snoqualmie’s standards, you could easily trigger shallow slabs on steep slopes at mid and upper elevations. Look for lower angled terrain to avoid this problem.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    The crowns from Sunday’s small natural storm slabs are pretty compelling evidence suggesting that this problem will only grow as we add more snow. Even though storm totals might appear modest, they add to a series of small storms each of which brought 2-5” of snow over the past few weeks. You can use uptrack tests, hand pits, and small slopes to see how the new snow reacts. However, there are also a few potential weak layers in the upper snowpack that may require a shovel to observe (see discussion for details). You may trigger a storm slab avalanche on any open slope greater than 35 degrees. On Sunday, natural avalanches tended to occur on steep convex rollovers in the terrain. While we don’t anticipate these slides growing large enough to bury you, they could easily knock you over and hurt you by pushing you into a tree, rock, or gully. As more snow piles up in the afternoon, these slides should only get deeper and possibly easier to trigger.

    (3/13/2022)

    Very small natural storm slab avalanches Sunday (3/13) on the north slope of Chair Peak. Notice these slides all occurred on very steep convex rollovers. 

    Photo: Shane Robinson

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Near and below the rain-snow line loose wet avalanches could be an issue. While the lower elevation snowpack has been through a lot this winter, a few inches of wet heavy snow and significant rain could cause the surface to become ripe to slide. If you find wet and sticky snow or see new rollerballs, expect loose wet avalanches. Fortunately, these slides should stay relatively small and not pose much of a risk. Just make sure to consider them before you traverse across a steep slope above a creek or cliff. Terrain traps like these can significantly increase the consequences of even small avalanches.

    (3/11/2022) Wet sticky snow like this lets you know the surface may be becoming unstable. Photo: Dallas Glass

Avalanche Discussion

Sunday’s storm at Snoqualmie brought 4-5” of snow to the upper elevation terrain. While this did result in a few storm slab and loose dry avalanches, unexpected sunshine combined with warm temperatures to also make the snow surface wet and sticky. Several travelers reported rollerballs, natural point release slides, and a few human-triggered loose wet avalanches. 

At mid and upper elevations a very aspect snowpack formed over the past few weeks. On southerly slopes, a series of melt-freeze crusts have allowed recent snow to bond well. Depending on the slope, these tend to eventually merge into the very prominent Early March Crust. In shaded terrain, three layers are worth noting. The 3/12 crust formed during warm weather this past week. This is often a thin and breakable crust near the base of the new snow. A layer of 1-1.5mm facets can frequently be found above the very prominent and thick Early March Crust. Until now, these weak grains have generally lacked a slab over them. Will this storm cause that to change? We’ll have to wait and see. Fortunately, the Early March Crust is very thick and strong. Right now, we do not have any layers of concern below this easy to identify snowpack marker. 

At lower elevations, the snowpack continues to be very well consolidated. Instead, you may encounter challenging travel with rough surfaces, icy slopes, wet heavy snow, frozen debris, and open creeks.

Régions couvertes