Boletín de aludes

Swan Range

Flathead Avalanche Center
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Peligro de aludes

Wed
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Dangerous avalanche conditions may develop throughout the day. Heavy snowfall rates will cause new snow to slide easily with the weight of a human or machine. If you see 8 or more inches of new snow fall today, stick to slopes 35 degrees or less and stay out from underneath large avalanche-prone terrain.

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    If the weather forecast verifies, the avalanche danger will rise to considerable with roughly a foot of new snow expected today. This rapid change will cause slabs to become more reactive and dangerous as the day progresses. Utilize small test slopes to see how the new snow is bonding to the old snow interface. If you see shooting cracks or can trigger small avalanches, dial back your terrain choices and choose simpler terrain.

    (12/12/2021)

    Fracture lines from avalanches that released mid-storm on Whitefish Mountain in the central Whitefish Range. This area picked up 2 feet of new snow over the weekend of 12/11-12.

    Photo: Pete Costain

Avalanche Discussion

Weather models and forecasts upped the ante this morning. The Whitefish Range, Flathead Range, and Glacier National Park may see up to 8 inches of new snow by nightfall. The Swan Range raises the stakes with possibly 12 inches of new snow. Snowfall rates may reach an inch an hour for the greater part of the morning.  This new snow will sit on stiff windboard, broken precipitation particles, or near-surface facets. These surfaces, especially near-surface facets, can act as a weak layer for new snow to slide on.

How do you manage your terrain today? Pay close attention to how much new snow accumulates. Fold your hand and choose a new game with lower stakes if you see 8 inches of new snow pile up. Great riding will be had in terrain with mellow slope angles and no overhead hazard. New snow may form slabs, or may be cohesionless and sluff easily in steep terrain. Shooting cracks are your sign that the new snow is forming slabs and will become more dangerous. Expect moderate danger if you see less than 6 inches of new snow fall today. For this scenario, manage your sluff with defensive riding strategies and continue to monitor new snow depths. Be ready to dial back your slope angles with increased precipitation.

The December 11th storm packed a punch with snow totals reaching up to 30 inches in many parts of the forecast area. This storm fell right-side-up and bonded well to the old snow interface. Many observations pointed towards signs of stability (observation 1, observation 2, observation 3), however, we received a report of what appeared to be a large natural avalanche in the Whitefish Range (observation 4). This avalanche failed in steep, rocky, complex terrain. If conditions point you towards stepping out into larger terrain today, hedge your bets by choosing planar slopes with good run outs to avoid the off-chance of a small avalanche stepping down to a larger, more destructive avalanche today. I suspect these slopes to be isolated to upper elevations, or in areas of the Swan Range where a freezing rain crust exists about 2 feet below the surface. 

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