Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Sun
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

Additional snowfall will maintain dangerous avalanche conditions at Snoqualmie Pass on Saturday. Slabs could break at any number of interfaces and be large enough to bury and kill you.  With so much uncertainty around old weak layers and complex weather patterns, you must choose simple terrain and let this storm run its course.

Problèmes avalancheux

  • Storm Slabs

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

    The snow will keep piling up, creating new interfaces and testing older ones. Failures could occur within the new snow or at its base. With crusts already in place, a good bed surface awaits for avalanches to run on once they fail. In some locations, you may see snow start to break into old snow layers, resulting in widely propagating slabs. Throw it all together, and this is not your standard storm cycle, so don't treat it as such. Weak snow, multiple crusts, and spotty distribution of old surfaces will complicate avalanche problems and render your ability to use our typical tips and tricks ineffective. Digging hand pits or using test slopes to gauge the storm snow's reactivity will only apply to that particular spot. Don’t feel confident extrapolating those results to other locations. You could test a slope, walk just a few feet, and find something completely different. Slabs will be larger as you ascend in elevation or wind-loaded terrain, increasing the possibility of them breaking into older, weaker layers. Don't roll out your standard storm day playbook, the likelihood of human-triggering may teter on very likely. Take a step back and choose appropriate terrain for the high level of uncertainty that currently exists.

    (1/11/2025)

    One of the numerous slab avalanches that occurred last time we got snow over a crust. Weak snow was suspected to have been involved in at least some of the slides that day.

Avalanche Discussion

After a month of high and dry weather created a weak and variable snowpack, a potent storm slammed into Snoqualmie Pass on Friday. Fluctuating freezing levels, strong winds, and heavy precipitation created touchy avalanche conditions. The Summit at Snoqualmie Pro Patrol reported slabs were reactive to both ski cuts and explosives throughout the day and that mixed precipitation reached the top of Alpental. A new surface crust formed as temperatures dropped, but snowfall quickly buried it. Further up the Alpental Valley, avalanche professionals reported touchy storm slabs in the morning hours and natural activity as a warm-up destabilized the storm snow.  As we set our sights on Saturday, continued precipitation and lowering temperatures should result in snowfall for the rest of the weekend. Strong to very strong winds will impact the zone, drifting snow into thicker drifts in exposed areas. Take extra care around those classic wind-loaded areas such as convex rollovers, leeward ridgelines, or rocky terrain such as the base of cliffs or sides of gullies/chutes. Natural avalanches could occur during or shortly after periods of strong winds or heavy precipitation.

As alluded to above, January's snow drought left us with plenty of weak snow on and near the surface. Variable has been the name of the game, with no discernable pattern in the distribution of surfaces. Near-surface facets, surface hoar, melt-freeze crusts, and wind-affected snow were intermingled throughout the landscape, often within feet of each other. The weak grains haven't been a problem to date, but now the time has come. This storm is building the required slab over them, and eventually, some slopes will reach their tipping point. Crusts will make an excellent sliding surface for any potential avalanche, and weak grains could result in more persistent-style slabs. We aren't jumping right into a persistent slab avalanche problem due to the spotty distribution of weak snow, but we may get there. You could see more surprising slides on shaded slopes and more failures on a crust on sun-exposed slopes but don't fully take that to the bank.

The take-home point is that we have a unique snowpack setup for our region and are in the midst of a standard Cascadian storm. Multiple long-time avalanche professionals have mentioned that the last time we had a similar snowpack was in 2017-2018, which resulted in 7 deaths throughout the Cascades in roughly a week. You can read the accident reports here to re-familiarize yourself. Needless to say, many professionals are on edge about how the next few weeks will play out. And that starts with Saturday.

So dial your terrain choices way back, and let the storm play out. We know everyone has pent-up desires after a lackluster January in the snow department. Take a moment to think and get your head back into the avalanche game after your mid-winter break. And please let us know what you see out there, avalanches or not, by submitting an observation. Now is the time for information sharing within the community. 

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