Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 7 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A sensitive, buried weak layer is keeping the avalanche danger elevated in the Swan Range. Two recent remotely triggered slides confirm that dangerous avalanche conditions exist. The best way to manage this problem is to select lower-angle terrain that is not connected to steep slopes. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Observers report an impressively thick and well-preserved layer of surface hoar in the Swan Range. We assume that this weak snow was responsible for the two recent remotely triggered slides near Mt Aeneas (see attached image). 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 two or three feet deep on wind-loaded slopes.

    The weekend heat wave and recent elevated wind speeds stiffened last week's snowfall into a cohesive slab on many slopes. As evidenced by recent slides, these can be triggered remotely from flat terrain above, to the side, and below steep slopes. 

    Cracks beneath your skis or machine indicate you have found a slab, while cracks shooting away from you indicate a sensitive slab. This is a near-surface problem, and hand pits are a good way to confirm the presence of surface hoar.

    Choose low-angle slopes that are not connected to steep slopes for a safer, more enjoyable experience. 

     

       

     

     

    (1/31/2026)

    Riders traverse over hard slab debris from a remotely-triggered avalanche on a wind-loaded slope. We assume this slide failed on a buried layer of surface hoar. The hard slab formed from consistent, moderate-to-strong southwesterly winds that transported the recent 10+ inches of new snow. 

Avalanche Discussion

Tricky avalanche conditions are developing across the area as weak snow and crusts formed during the January drought are now capped by a slab in many locations. This morning, we transitioned from a Storm Slab problem to a Persistent Slab problem in all zones. We are keeping the danger rating at CONSIDERABLE in the Swan Range today, with the plan to drop to MODERATE on Tuesday.

Swan Range - A widespread, well-preserved surface hoar layer was the culprit in two remotely triggered slides on Friday and Saturday (Observation, Observation). The Swan Range remains our primary concern because surface hoar may persist for extended periods, can be remotely triggered, and produce avalanches wider than expected.

Whitefish Range - Friday, observers noted long shooting cracks in the surface slab that became cohesive during the mid-day warm-up (image).  On Saturday, a motorized observer triggered a small, soft-slab avalanche in the northern part of the range (Observation). This slide most likely failed due to the weak-layer + crust setup, but did not propagate widely because of the soft nature of the overlying slab. On Sunday, Rob and Lloyd conducted a FOFAC Level 1 motorized class in Kimmerly Basin (southern Whitefish Range), where they obtained pit results of ECTP 1 and 2 on buried surface hoar 15 cm down on a mid-elevation north aspect.  At the same time, a Level 1 avalanche class noted a developing surface slab (image) in the southern Whitefish Range. 

Flathead Range/southern Glacier Park - Challenging access has limited observations from this zone. Josh and Mike traveled to the Skyland area on Sunday and found buried surface hoar under 4-6" of recent soft snow. The only locations where this weak layer was a concern were along ridgelines where the wind had stiffened the recent snow into a slab (Observation). An experienced group visited southern Glacier Park and encountered a variety of snow conditions. Above 6000 feet, a very thin crust capped 3-8 inches of soft snow. Lower down, corn gave way to mank, ending with substantial blow-down on the valley floor (Observation). 

February 2nd is Groundhog Day, the midpoint between the shortest, darkest day of the year on the winter solstice and the spring equinox.

 

 

 

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