Bulletin d’avalanche

Swan Range

Flathead Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 6 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering a large avalanche on a buried weak layer remains possible. Due to recent snow and wind, expect slabs to thicken with elevation and below areas of wind affect, such as ridgelines, saddles, or mountain tops.  Acknowledge the signs of collapsing and whumphing, while avoiding steep slopes without a stout surface crust. Enjoy another day of easy travel and sunshine on southerly facing slopes.

Problèmes avalancheux

  • Persistent Slabs

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

    A widespread weak layer of facets or buried surface hoar exists. Upper-elevation shaded slopes with a dense surface slab are the most likely places to trigger a large avalanche.  Expect the slab depth to increase with elevation and in areas that collect snow from typical wind directions. 

    Travel advice, at its simplest, is to stay on a stout surface crust. If you choose to recreate on shaded slopes, look and listen for clues of instability and maintain distance from steep slopes above or to the side of your location. Avalanches failing on a buried weak layer may be triggered remotely. Collapsing was reported in both the Swan and Whitefish ranges yesterday (Wednesday). This is a clear sign you’ve found a sensitive weak layer with a slab above it. 

    A 1 to 2-foot slab sits atop a widespread layer of buried surface hoar. A stout, supportable crust at the surface on southerly-facing aspects provides the safest route of travel to avoid tangling with this persistent slab problem.

    (2/10/2026) Photo: Guy Zoellner

Avalanche Discussion

The persistence of a buried weak layer remains across the forecast region. It’s hard to let our guard down when we have Extended Column Test scores being reported with easy to moderate force, and audible collapsing is reported in 2 out of 3 mountain ranges. Despite a long spell of sunny skies, light winds, and very little precipitation, the snowpack continues to show signs of instability in isolated areas.

We have dropped the Swan Range danger rating in the upper elevations. Due to dribs and drabs of recent snow, coupled with moderate winds, the slab sitting on the weak layer is likely thicker (1 to 2 feet) here than in other zones. The most concerning buried weak layer consists of large crystals of surface hoar atop a crust. This combination could produce large, remotely triggered avalanches. A grey stripe will easily give away the weak layer while digging. Stout surface crusts in the Swan are safe travel routes to avoid the current avalanche problem.  

The Whitefish range has only had a few inches of snow in the last several weeks. Despite this, observers reported reactive test results from a buried weak layer 25 cm below the surface yesterday (Wednesday). Another observer noted the surface crust breaking down and faceting on northerly slopes.

A welcome change in the weather pattern is expected this weekend. If we add a significant load to these buried weak layers, the conditions could change rapidly.

Régions couvertes