Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

Riders have been caught, carried, and buried by large avalanches during the last week. You can trigger avalanches from a distance or on connected low-angle slopes. Plan your route to give a wide buffer to any steep slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    We received another report of a remotely-triggered avalanche on a buried weak layer, this time near WMR. This has become common since a layer of weak snow and surface hoar was buried in late January.  Large and destructive avalanches breaking 2 to 3 feet deep have been triggered from low-angle slopes well above, below, or hundreds of feet away from typical start zones. Several riders have been caught, carried, and partially or fully buried, even as they try to avoid this problem. 

    The hotspot for activity has been slopes facing northwest through east to southeast. When dealing with an unruly layer like this, a simple approach is best: stay well back from steep slopes where the problem exists. 

     

  • Storm Slabs

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

    1 to 2 feet of recent storm snow blankets portions of the advisory area.  Cold temperatures have delayed its settlement. Storm snow can remain reactive as the slab consolidates, especially where it rests on a crust or has been thickened by wind.  Observations from Friday noted small slab avalanches on sheltered and windward slopes. Cracking in the snow's surface implies that slabs are reactive to the weight of a rider. If you like to use test slopes to assess storm instability, recognize that the amount of recent snow can result in large avalanches on even small slopes.  This is especially true if it steps down to a buried weak layer.  Make sure you don't bite off more than you can chew. 

    Dry Loose: It will be possible to trigger sluffs on steep slopes where recent snow remains unsettled. Small sluffs may run naturally on very steep slopes that receive direct sunlight, especially those with rocky outcrops. Choose slopes that allow you to escape sluffs by moving across the fall line. 

    You may still find soft slabs in areas favored by recent snowfall.  These will be most reactive where the slab rests on a crust or has been stiffened by wind.

Avalanche Discussion

These are the days that forecasters dream of, but not in a good way: fresh snow and sunshine luring weekend crowds onto an unruly persistent weak layer. With this in mind, FAC released a Special Avalanche Bulletin on Thursday 2/19. This is the best tool we have for communicating particularly dangerous avalanche conditions when the rating is less than HIGH. We even got on the phone to call local outfitters and operations.

The current persistent slab problem is remarkable. One longtime local and doctor of snow described it as the “touchiest they’ve seen in maybe 10+ years.” Similar conditions resulted in a fatality near Fernie, BC, on Tuesday.

As you aim to avoid the large avalanches on a buried weak layer, don’t overlook hazards in the recent snow. We’ve received plenty during the last week. This will make it difficult to find any steep slopes to travel on safely. Don’t get caught trying to thread the needle. 

Regioni coperte