Bulletin d’avalanche

West Slopes South

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 6 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

A weak upper snowpack may be stressed by rising temperatures or recent wind loading. This is not your standard Cascadian snowpack, so don't treat it as such. Make trip plans that limit or eliminate your exposure to slopes steeper than 30 degrees.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2.5

    You need to continue to make travel plans that account for persistent weak layers in the upper snowpack. These layers may not provide direct feedback to you as a traveler, but they exist and are capable of producing surprising avalanches. Slabs may break widely or even trigger remotely (from a distance) if they fail. Red flags such as long shooting cracks, whumpfing collapses, and widely breaking avalanches are all signs that the snowpack is unhappy, but are not guaranteed to occur before a slab releases. The greatest uncertainty surrounding this problem remains the likelihood of triggering. 

    With recent wind-loading and now a warm-up on the horizon, avalanche activity on these layers could be on the rise. Earlier this week, we saw an uptick in activity as temperatures warmed on Tuesday. Don't treat Saturday like a standard bluebird weekend - this problem is different.

    Our normal tips and tricks for evaluating stability won't work. Uptrack tests, small test slopes, and even hand pits can't give you a sense for where or how these weak layers will fail. Your best management technique will be to avoid all open slopes over 30 degrees. That includes wind-loaded terrain and even large openings in treed areas.

    (2/27/2026)

    A widely-breaking avalanche in the Sourdough Range of Mount Rainier National Park. This one doesn't have a confirmed failure date, but you can bet it's persistent by how wide it is.

    Photo: Crystal Mountain Pro Patrol

  • Loose Wet

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

    With temperatures on the rise and more sunshine in the forecast, wet avalanche activity may follow. Look out for wet avalanches anywhere the snow surface is getting moist. If you see snow shedding from trees and rocks, or fresh pinwheels and rollerballs, then you'll know the snow surface is destabilizing and wet slides could soon follow.

    This avalanche problem is typically easy to manage, but with persistent weak layers lurking below the surface, it becomes more complex. In addition to fanning out and growing in size as they descend, the threat now exists that they will trigger larger and more dangerous persistent slab avalanches. 

    If the mountains start to fall apart in the heat of the day, head for shaded, low-angled slopes, keeping aware of the terrain above you.

    (2/27/2026)

    Loose avalanches that failed due to sunshine and rising temperatures in the White Pass backcountry. Many of these originated as snow shed from trees or rocks.

    Photo: Dallas Glass

Avalanche Discussion

Observations of widely breaking avalanches continue to pour into our inbox. We've been notified of shooting cracks, whumpfing collapses, or atypical avalanche activity every day since Saturday, the 21st. That's good confirmation that the snowpack has been uphappy and is letting us all know. 

The unhappiness arises from two persistent weak layers that exist within the top couple of feet of the snowpack. The 2/13 buried surface hoar and 2/7 crust with facets have been identified as a problem near Crystal Mountain, White Pass, and parts of Mount Rainier National Park. We do not have any snowpack information from the southern volcanoes, but webcam imagery and seismic data provided to us from our friends at the USGS lead us to believe the problem exists there as well. This snowpack structure is atypical for the Cascades and has most avalanche professionals on edge. 

At the tail end of the workweek, wind loading throughout the zone was significant, building thicker, stiffer slabs over all that weak snow. Management of these wind slabs is largely the same as for the persistent slab problem: avoidance. You likely won't find one problem without the other. 

As we look forward to the upcoming weekend, the winds should die down and be replaced by sunshine and rising temperatures. This will add a layer of uncertainty and complexity to an already unsettling time in the mountains. How will the generally cold and weak upper snowpack respond to the warmth? The answer is unclear. But any triggered avalanche, whether wind slab, wet loose, or other, could step down to those buried weak layers, producing very large and dangerous avalanches. 

Régions couvertes