Bulletin d’avalanche

Swan Range

Flathead Avalanche Center
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Danger d’avalanche

Wed
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 9 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

An Avalanche Warning is in effect. Very dangerous avalanche conditions exist. Avoid traveling on or below steep terrain. Large avalanches will fail naturally and run long distances.

Problèmes avalancheux

  • Loose Wet

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

    Rain on dry snow is a recipe for instant avalanching. The wet debris from these slides can travel long distances and be very destructive. If you decide to go out today, plan a route that avoids all avalanche terrain. That includes the runouts of large paths and steep terrain in mature forests. Don’t let the tall alder at low elevations fool you into thinking it is safe from above.

    (12/13/2024)

    Debris pile and track from a large (D3) wet loose avalanche on the north face of Mount Penrose.  This likely occurred during an early-season warming event, similar to today. 

    Photo: Flathead Avalanche Center

  • Wind Slabs

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

    Wind speeds are cranking; hourly averages are above the threshold for drifting snow into thick, hard slabs. Avoid traveling on or below terrain that is being actively loaded by wind-drifted snow.

    Yesterday (Monday), we triggered slab avalanches and initiated shooting cracks on small test slopes. Expect more of the same today, and expect large avalanches to fail naturally. A human-triggered or natural avalanche that starts at upper elevations will travel long distances and entrain dense, wet snow below, making it difficult to survive. Avoid being on or below steep terrain.

    (12/7/2025)

    Common example of windloaded terrain along the Continental Divide from strong West winds with snow available for transport. 

    Photo: Michael Reavis

Avalanche Discussion

A potentially historic atmospheric river event is leading to very dangerous avalanche conditions. Rain on snow and heavy snow are overloading the snowpack. In the last 24 hours, remote weather stations are picking up anywhere from .75 to 2+ inches of Snow Water Equivelent and growing. Yesterday (Monday), we received reports of very large avalanches running to lower elevations (see photo). Overnight, high precipitation intensity and strong wind speeds likely led to a significant round of natural avalanches.

Today, a brief lull in precipitation and cooling temperatures should slightly decrease the likelihood of natural avalanches, though it’s nothing I’d hang my hat on. Rain on dry snow and warm temperatures often lead to impressively large avalanches that travel far distances. Complex avalanche conditions should lead to simple terrain selection. That includes choosing routes free of overhead hazards and avoiding steep slopes. I’d give all avalanche terrain, big or small, a wide margin today.

Looking ahead, we are in for another round of snow, rain, and strong wind tomorrow (Wednesday). Expect very dangerous avalanche conditions to remain in place until the storm passes.

Régions couvertes