Bulletin d’avalanche

East Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions will continue due to a weak snowpack structure. You can trigger unsurvivable, very large avalanches on weak layers  2-4 feet below the surface, especially where the wind has piled the snow even deeper. Avoid being on or under terrain where very large avalanches could start or run from above, and stay out of large and overlapping avalanche paths.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    Very large natural and triggered avalanches were reported on older weak layers on Saturday; see photo here and more below.  Put a large buffer of terain between your group and large start zones and complex avalanche paths above 6,500ft.  Choose smaller, well-supported slopes and stay out from under large overhead terrain. If you see cracks shooting through the snow or feel whumphing collapses, stick to slopes under 30 degrees. 

    A recent load from snow and wind has stressed the underlying weak snowpack structure. Look for strong-over-weak snowpack structure and sudden or propagating snowpack tests results to help you identify the problem. The most problematic slopes will be where you find a thin weak layer layer of facets over Feb 25th interface (sometimes a crust 1-2.5' below the surface) and the Jan 31st crust, 2-4' below the surface. Observers reported very large natural avalanches in the past week, some that are suspected to have run on this weak layer. This same weak snowpack has already been the source of numerous close calls and one fatality in the Eastern Cascades.

    A very large avalanche was triggered by skiers on 3/2 on Kangaroo Ridge. This broke very widely and ran almost the entire length of the path. We suspect this ran on a persistent weak layer.

    Pk 8183, WNW, 7,600ft

    (3/2/2024) Photo: Willie Webster

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    You're most likely to trigger avalanches in the recent layers of snow near the surface or where the wind has formed subtlely stiffer slabs. Small, loose avalanches in recent storm snow will be easy to trigger on steep, wind-sheltered slopes. If enough sun gets through the clouds, avalanches could become easy to trigger on southern aspects.

    Take time to test the new snow on inconsequential slopes before traveling in terrain steeper than 35 degrees. Avalanches at mid and upper elevations could be unsurvivable. There, you will need to manage the more deadly consequences of persistent slab avalanches and avoid large avalanche terrain all together.

    (12/20/2021)

    Example storm slab avalanche on a small slope.

    Photo: Adam Butterfield

Avalanche Discussion

Preliminary Report: An avalanche accident occurred on Friday, March 1 near Darland Mt in the Ahtanum Meadows area (East South zone). Two snowmobilers were involved in the slide. One rider was fully buried and killed. The avalanche occurred around 6600ft in a generally east-facing bowl. NWAC staff will visit the accident site on Saturday. Our deepest condolences to the family, friends, and community.

Signs of instability have been abundant in the past week and dramatically so on Saturday. Multiple close calls and numerous snowpack observations in the Highway 20 corridor point to a couple of buried weak layers (2/25 and 1/31) in the top 2-4 feet of the snowpack. On Saturday, an NWAC observer witnessed another group trigger a widely breaking, very large avalanche on Kangaroo Ridge. It ran almost the entire length of the avalanche path. While we can't confirm, we suspect this ran on one of the persistent weak layers. More details on the Kangaroo Ridge avalanche can be found in the photo caption below and in this observation. In a sepereate event on the southeast sholder of Cutthroat Peak (6,400ft, SE) a party remotely triggered avalanches that propagated to either side of them 800-1000ft after leaving a profile site that they dug on the slope. A number of other very large natural avalanches have been reported, mostly from upper elevations, that appear to involve deeper weak layers.

On Thursday, a group of skiers near Cutthroat Lake (7,100ft, SE) felt a very large collapse and observed cracks that broke several hundred feet across and down the slope. While no avalanche occurred, a quick profile determined a weak layer of facets was 60cm down near a crust. Since Wednesday, observers reported a widspread cycle of avalanches, some up to size D3. While many avalanches likely occured within the recent snow from the last week, we suspect some may have ran on older weak layers. Earlier in the week,  observers near Blue Lake found whumphing collapses and confirmed the instability was on a layer of faceted snow 2ft down above the late January crust.  

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

Régions couvertes