Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
Voir sur la carte

Danger d’avalanche

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

Points saillants

The threat of avalanches on buried weak layers should dictate your terrain selection on Saturday. Make travel plans that steer you well away from large open slopes where this problem is more likely. A lack of observed avalanches or whumpfing collapses does not indicate stability.

Problèmes avalancheux

  • Persistent Slabs

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

    Don't ignore the well-documented poor snowpack structure we have at Snoqualmie Pass. Rather, use it to drive your terrain selection on Saturday. Below the light and fluffy snow, buried weak layers 2-3 feet down consistently produce poor snowpack results, particularly on shaded aspects. The big question mark revolves around the likelihood of triggering. This problem likely won't give you any feedback that a slope is unstable until it releases. The only way to get any information about it is to dig down and take a look for yourself. Even then, your test results are only one piece of the puzzle and may not apply to nearby slopes. So what can you do? The best choice is to avoid large open terrain where triggering one of these slides would have devastating consequences. Instead of gambling, stick to small low-angle or treed slopes.

    (2/2/2025)

    This avalanche occurred after an audible whumpf. The slide failed on facets over a crust and released the entire width of the feature. NE, 3700ft

    Photo: Summit at Snoqualmie Professional Patrol

  • Wind Slabs

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

    Above our weak interfaces is plenty of recent storm snow that you may need to manage on slopes over 35 degrees. We’re wrapping this into a wind slab problem since wind-loaded slopes will be the most likely location to trigger an avalanche large enough to call consequential. With such low-density snow, blowing it around into shallow piles near ridgelines or the base of cliffs doesn't require much wind. Look for actively blowing snow, fresh cornices, or large pillow-like drifts to help identify wind-loaded features to avoid. You’ll know if you hit a wind-affected area because the snow should be stiffer than the light and fluffy found elsewhere. 

    In sheltered terrain, you may see loose avalanches running in the surface snow. Most of these should be small enough to call inconsequential but don't get caught off guard near a terrain trap.

    (2/6/2025)

    A large avalanche on Mount Snoqualmie. The failure layer is unknown. We suspect it failed on 2/5. [N/NE 6100' Crooked Couloir]

    Photo: Eddie Schoen

Avalanche Discussion

We've had a busy first week of February hunting down persistent weak layers within our snowpack. If you haven't been reading the forecast daily, we know of 3 persistent slabs that failed within our zone and a handful of whumpfs. The most recent direct feedback was Wednesday when The Summit at Snoqualmie Pro Patrol reported a whumpfing collapse followed by a small but deep avalanche (SW 5400'). The layers in question are the January Drought Layer (JDL) and the 1/10 complex. The setup will look a little different depending on where you look, but generally speaking, the JDL sits below a thin melt-freeze crust and consists of ~5cm of faceted snow over the more robust 1/10 complex. This weak structure is anywhere from 2-3 feet below the surface. Test results continue to suggest that these layers can propagate a fracture given the right trigger, including propagation saw tests repeatedly failing with cut lengths around 35 cm [PST35 END].

So what can you do about it? Well, not much. The structure is there and well-documented. We have been getting some feedback from it with those whumpfs and a handful of avalanches, but by and large, it won't speak to you as you travel. Conditions may "feel safe" as you travel through the beautiful snow. But now you're too smart to be fooled by that trick. You know the poor structure trumps snowpack tests or lack of whumpfing. Avoidance is the only solution. So, don't roll out your typical playbook and terrain selections. Please keep it simple and try to fight the inviting new snow on slopes you know are potentially dangerous. 

Above the persistent issues, the snowpack is generally right-side-up with a few interstorm layers and subtle melt-freeze crusts. Another shot of snow and an uptick in winds is expected on Saturday. You should manage the upper snowpack like typical post-storm snow on slopes over 35 degrees. But remember what's down there. On Thursday, an avalanche professional reported a large avalanche on Mount Snoqualmie. The failure date is unknown, but we suspect it occurred on 2/5. It looks similar to a large wind slab, but we can’t rule out that persistent grains were involved, especially given its aspect and elevation (N/NE ~6100’).

Régions couvertes