Bulletin d’avalanche

Swan Range

Flathead Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 5 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Large, destructive natural avalanches have occurred in the mountains as recently as yesterday. While the danger is slowly decreasing, the consequences remain severe. Give steep slopes and their runouts a wide margin today.

If you are headed to the northern Whitefish Range (e.g., Ten Lakes) or the southern Swan zone (e.g., Six Mile area), build in an even larger margin of safety—conditions there have been warmer and wetter.

Problèmes avalancheux

  • Persistent Slabs

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

    Deeply buried weak layers formed in January are being stressed by recent rain and prolonged warming. A gradual cooldown at the surface today will not immediately improve conditions at depth. Avalanches failing on this layer can break 3 to 5 feet deep (or more on wind-loaded slopes) and thousands of feet wide.

    Human-triggering will be difficult, but not impossible—especially from thin spots such as rocky outcrops or near trees. A more likely scenario is a smaller avalanche in the upper snowpack, or a falling cornice, stepping down to trigger a much larger, deeper release on the January Drought Layer.

    The only reliable management strategy is avoidance. Give steep slopes facing NW-N-SE a very wide margin.

    Wet Slab: After significant rainfall and several days without a refreeze, liquid water has weaseled its way into the snowpack. While observations have not consistently shown water penetrating deep enough to drive widespread wet slab activity, we have seen at least one suspected wet slab near Condon, and the potential remains—especially in the northern Whitefish and southern Swan. The distinction between wet and dry slab isn’t too important today, and the travel advice remains the same: avoidance of steep slopes.

    (3/21/2026)

    Large avalanches can break widely. Stay far back from steep slopes and their start zones. 

    Photo: Josh Lipkowitz

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–3.5

    Last weekend's snow and wind grew impressive cornices along alpine ridges. Sustained above-freezing temperatures and rain have weakened these overhanging ledges of snow, and failure remains possible. Tumbling chunks of snow can cause large avalanches to fail on buried weak layers. Stay well back from the edge if traveling along ridgelines.

    (3/20/2026)

    Rain and warming have weakened cornice across the region.  Tumbling cornices can often trigger large avalanches on the slopes below. 

     Photo: Adam Clark

Avalanche Discussion

Today’s cooling trend will bring a welcome reprieve from the sustained warm, wet conditions of the past week. While our bodies will notice this change quickly, deeper layers in the snowpack will not. The slab continues to change, and though the spigot will shut off at some point today, the water in the hose still has to make its way through the snowpack. Where it winds up, we don’t yet know.

Water movement through snow is highly variable, even on the same slope. Combine that with differences in prior snowpack structure and a very different weather pattern across the advisory area during this warmup, and you end up with a lot of uncertainty. The Flathead appears to have experienced the most significant rainfall and melt, with Tunnel Snow Station losing a staggering 34” of snow over the past week, while most other stations have lost 9–11”. Rain reached far higher in the Flathead Range—up to roughly 8,000’—whereas in the southern Whitefish and northern Swan, runnels generally stopped around 6,000–6,500’. The Flathead Range remains primed for big avalanches today. 

Even as danger drops from high to considerable in the Swan and Whitefish Ranges today, caution remains critical—large, destructive avalanches are still possible. When the January Drought Layer fails, it fails massively. Yesterday on Lost Johnny, we observed a slide that crossed two faces, breaking over 4,000’ wide and more than 6’ deep at its thickest point. This is the scale of what we’re dealing with.

In many start zones above 6,500’, the JDL remains dry and intact. This layer will continue to guide our travel decisions, likely for the rest of the season.

Régions couvertes