Bulletin d’avalanche

Swan Range

Flathead Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering a large avalanche on a buried weak layer remains our primary concern.  Sunny slopes with a stout, supportable crust offer the safest option for navigating this challenging problem. Today's light rain may wet previously dry snow and initiate small loose slides. 

If today's storm overproduces, the danger may rise on slopes without a strong crust, where the threat of large natural and human-triggered avalanches may increase.

Problèmes avalancheux

  • Persistent Slabs

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

    An impressively thick, well-preserved layer of surface hoar was responsible for rider-triggered slides, collapsing, and cracking in the Swan Range last weekend, 1/31 and 2/1. This layer is identified by a grey stripe in pit walls and lies within the top foot or so of the surface in sheltered terrain and around two feet deep on wind-loaded slopes.

    The recent heat wave has stiffened surface snow into a cohesive slab on polar aspects and a crust of varying strength on sunny slopes. You may not notice signs of instability, such as cracking or collapsing, before triggering a slide. These can be triggered remotely from flat terrain above, to the side, and below steep slopes. 

    This is a near-surface problem, and hand pits are a useful tool for confirming the presence of a buried weak layer.  

    Sticking to a supportable crust will minimize the risk of impacting the weak layer. Choose low-angle slopes that are not connected to steep slopes in areas without a crust. 

    Wet Loose: Today's forecasted rain may wet previously dry snow, resulting in small wet loose slides. If the freezing line rises higher than expected, this problem will become more widespread.

     

    (1/31/2026)

    This is a pile of hard slab debris from a remotely triggered avalanche near Mt Aeneas. We assume this slide failed on a buried layer of surface hoar on a wind-loaded slope. 

     

Avalanche Discussion

Cooler weather and precipitation return to the Flathead today through Monday. Decreasing temperatures will be a welcome relief after the previous 4 days of near-record warmth. During the heat wave, temperatures peaked on Thursday, with upper-elevation stations reaching 50°F (image)!

Today's precipitation is forecast to be light, with a stronger pulse expected overnight. If this storm overproduces today, the danger may rise on slopes without a strong crust. Rain or snow could impact the buried weak layer by adding weight to the surface and possibly triggering a large avalanche. Rain may wet dry snow, resulting in small, wet, loose slides on northerly terrain.

Sustained sunshine and warm temperatures triggered natural slab avalanches on sunny slopes in the Flathead Range (image, image, image). We assume these failed on a buried weak layer that has been responsible for this past week's avalanche activity, including rider-triggered slides in the Whitefish Range (image, image), the Swan Range (image), and the Flathead Range (image).

This week's balmy conditions wetted the top 10+ cm on many sunny slopes, forming a crust. Cooling temperatures should make this layer supportable to riders in many locations. This strong layer will minimize the impact of both your weight and the incoming snowfall on the weak layer, and will be the safest areas to ride.    

Polar aspects remained mostly dry below the top few centimeters of the surface. These slopes remain the most dangerous and will be tested with the incoming snowfall, especially on wind-loaded slopes. Caution should be used when traveling in areas without a supportable surface crust.

Régions couvertes