Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
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

Recent avalanches on deeply buried weak layers combined with new snow and wind are keeping the avalanche hazard elevated. Even if you don’t see recent avalanches or experience cracking or collapsing, don’t let your guard down—the snowpack is still dangerous. Steep, open slopes facing east, north, and west could produce avalanches large enough to bury, injure, or kill. The safest move is to stick to lower-angle terrain or head for the forest, where you'll find great snow and safer conditions. 

Problèmes avalancheux

  • Persistent Slabs

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

    Recent avalanches, rumbling whumpfs (would-be avalanches if the slope was steeper), and repeated poor snowpack tests all tell the same story. It is possible to trigger persistent slab avalanche on steep open slopes on the northern half of the compass, where 2-3.5 ft of snow has capped multiple well-documented weak layers. There are signs of this problem at all elevations. While all notable results have been on the northern half of the dial, we don't yet have full confidence that you couldn't find this problem on an isolated south-facing slope, especially on slopes that are somewhat locally protected from direct sun.  By itself, the nature of this problem should be enough to shape your travel plans, even in clear weather. With more snow and wind Wednesday and overnight into Thursday, a conservative tour plan is advised.

    Though the formation of these problems is complex, the strategy for staying safe is quite simple. Don’t try and outsmart this one. Tracks don’t mean a slope is safe, snowpack tests may not reveal the problem, and you likely won’t see obvious warning signs before a slope releases. Keep it simple—avoid steep, open slopes facing west, north, or east.   

    (2/2/2025)

    This avalanche released after a 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

  • Storm Slabs

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

    Another round of snow with increasing winds means that storm and wind slabs should be on your radar. Even if new snowfall doesn't amount to much, there are large quantities of snow available for wind transport which could add to the hazard. Slabs will be most sensitive in steep wind-loaded terrain below ridge lines, cornices, cliffs, and at the tops of gullies and chutes. Given the knee-deep depth of soft and unconsolidated snow out there, soft storm slabs could be a problem at all elevations, even out of the wind zone. By avoiding the persistent slab problem, you will also avoid the brunt of any storm/wind slab instabilities. If you are traveling in steeper terrain on the southern half of the compass or in the forest, feel for hard over soft snow and look for signs of wind-loading like blowing snow, textured surfaces, and lens-like deposits, and avoid slopes where you see those signs. Dry loose avalanches could also run fast and far in the fresh snow. An appearance by the sun may cause some show to shed from trees or make dry loose avalanches a bit more likely.

    This problem isn't the main hazard on Thursday, but, triggering one of these slides could step down into deeply buried weak layers and trigger a more substantial and consequential avalanche. 

    This skier triggered storm slab occurred in wind affected snow on Saturday. Photo: Kyle Rowe

Avalanche Discussion

Avalanche conditions remain complex at the Pass. NWAC forecasters and local avalanche professionals continue to note poor structure and propagating test results on deeply buried weak layers. They also noted minimal reactivity in the storm snow and generally excellent travel conditions in the conservative terrain where they travelled. A small breakable crust was observed down about 3" on steep south-facing slopes from Wednesday's sun, though this did little to impact the excellent riding conditions. Some snowpack tests seem to indicate the persistent slab problem may be getting just a bit harder to trigger below a stiffer slab, but the propagation potential for a deadly avalanche is still very much present. 

Sometimes these problems present with a rumbling roar, and other times they make themselves known with a more discomforting growl. At the Pass, we may still be in the discomforting growl phase. Don't discount this as there is every reason to be uncomfortable with the snowpack. Don't wait for your own rumbling roar to convince you to dial things back. The nature of persistent slabs are such that as we get further out from significant snowfall, the likelihood of triggering a deadly avalanche generally decreases, but the potential consequences don't change at all. Don't let the drop in top-line danger level impact your thinking about this problem, as very little has changed within the snowpack. These types of problems are number games. Many (perhaps most) slopes won't avalanche, some may, and there is no safe way to manage a problem like that. You have to avoid it. Remember, structure trumps individual pit results, and this snowpack structure isn't good. A 2-3.5 ft slab of snow has buried the weak January Drought Layer (JDL) comprised of facets, crusts, and surface hoar, depending on location. A bit below is the also suspect 1/10 crust complex complete with facets on top and within. Either of these layers could fail and it doesn't really matter which.

With a conservative tour plan that avoids steep open terrain on the northern half of the compass, you don't need to dig a pit to stay safe and have a great day in the mountains. If you do decide to dig, the purpose should be to help build a dataset that shows trends over time, not to clear a slope as stable. When we all put our observations together, overtime, we may be able to further isolate this problem to specific aspects or elevations. But, at the individual level, a pit is highly variable, and test results should not be used to assess a specific slope as safe. Remember, we didn't get here overnight, and this problem won't magically go away overnight either. 

Please help us hone in on this problem by submitting an observations. All obs are helpful, whether they involve a pit or not!

Régions couvertes