Bollettino valanghe

Swan Range

Flathead Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Open full map
Non aggiornato — questo bollettino è scaduto 6 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Shaded slopes above 6,000 feet harbor a weak layer buried 1 to 2 feet deep. A triggered avalanche will be large enough to bury or injure a person. South-facing slopes with a stout, supportable crust beneath the recent snow will provide the safest areas to recreate today.

If you see rollerballs forming this afternoon as temperatures rise, transition to areas with lower slope angles and move out from under rocky areas. While these avalanches will be small and relatively inconsequential, they could easily knock you off your feet if you’re on a slick, hard crust.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    A weak layer buried 1 to 2 feet deep exists on shaded slopes. You could trigger an avalanche on this layer remotely from a shallower slope below or further back on a ridgeline than you expect. Slab thickness will increase with elevation and in wind-affected areas.

    The best way to manage this problem is to let the surface crust thickness dictate your travel plans. A hard, stout, supportable crust that is beneath the few inches of recent snow is the safest route to go. Travel in places where you need sunglasses and your skis or machine are not breaking through more than 3-4 inches of snow. If you choose to ride in shaded terrain (i.e., better ski conditions), keep the slope angle low to provide a margin of safety.

    (2/10/2026)

    ECTP9 on the weak layer of buried surface hoar. Finding this structure, coupled with a breakable crust, steered us to ski a more Southerly aspect with a much more supportable crust.

    Photo: Guy Zoellner

Avalanche Discussion

Mountain travel right now is simple, yet tricky. The most alluring places are those that harbor the buried weak layer, possibly steering us to areas of the greatest danger. Recent snowfall has formed a cohesive 1 to 2 foot slab atop a buried layer of surface hoar or facets. Slabs are thicker (1 to 2+ feet) in the Swan and Flathead Ranges, and thinner (up to 1 foot) in the Whitefish Range. Areas downwind of ridgelines or mountain tops will have thicker slabs due to wind-drifted snow.

A round of natural and human-triggered avalanches occurred last week involving the weak layer. The snowpack structure is most worrisome on shaded slopes where a supportable crust does not exist. Signs of instability (shooting cracks, collapses) and recent avalanche activity have waned in recent days. The unanswered question is what could trigger an avalanche today? Recent extended column tests have failed with easy force, indicating this fragile layer of surface hoar can still propagate and cause an avalanche if triggered. 

Restraint is a management technique I’m using right now. Sticking to southerly-facing slopes with a very stout crust reduces the likelihood of triggering an avalanche on a buried weak layer. While not the best snow conditions on the mountain, it is the simplest way to avoid tangling with the possibility of triggering a large avalanche.

Regioni coperte