Boletín de aludes

Swan Range

Flathead Avalanche Center
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Peligro de aludes

Thu
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Southwest winds will transport 6 to 12 inches of low-density snow into fresh slabs. Manage your risk by avoiding these wind-loaded slopes and by paying attention to blowing snow and drifting dunes along ridgelines. A triggered wind slab may have the potential to impact weaker layers buried in the snowpack.

Problemas de aludes

  • Wind Slabs

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

    Southwest winds will transport the new low-density snow near and below ridgelines into 1 to 2-foot slabs. To find these, use your hand or ski pole to feel the texture of the near-surface snow. If it is stiffer or more consolidated, you've found a drift that may be dangerous if it's on a slope steeper than about 35 degrees and more than about 8 inches thick. Today's winds may continue to form pockets of stiff snow mid-slope that can be sensitive to a person's weight. Pay attention to the consequences of being caught in even small slides in terrain with rocks, cliffs, trees, and terrain traps.

    (1/30/2023)

    Older cornices along the ridge with pockets of new wind drifts from N winds in the Swan Range.

  • Loose Dry

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–1.5

    At upper and middle elevations, shaded and sheltered slopes will have new, cohesionless dry snow.  Before skiing or riding slopes steeper than 35 degrees, consider what terrain features are connected or below you.  Triggering sluff that leads to terrain traps, such as cliffs, tree wells, or gullies, can have deadly consequences.  Keep the lure of powder skiing and riding in perspective today.

    (1/29/2023) Loose dry avalanche unintentionally triggered by skier. Not caught.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–3

    Within the past week, riders have triggered avalanches on a buried layer of facets or surface hoar. Snowpits continue to reveal that this weak snow is present in various locations and reactive in tests. This layer is found on shady aspects 1-2 feet below the surface in the Whitefish Range, Flathead Range, and southern Glacier Park, and 1-3 feet below the surface in the Swan Range. Buried facets and surface hoar appear to be slowly gaining strength, but recent snowfall and wind continue to test this layer. The easiest way to manage this problem is through terrain selection. Continue to choose lower-angle terrain free of overhead hazards and convexities. Slopes with clean runouts are an excellent way to build a margin of safety into your day.

    (1/31/2023)

    Snowpit on SE aspect in the Swan Range.  Failed on a persistent weak layer 50cm from the surface,  ECT20.

    Photo: sw

Avalanche Discussion

Regarding avalanche hazards, the prevailing southwest winds will continue to be the driving force in building fresh 1 to 2-foot slabs. Wind speeds in the Whitefish Range and the Flathead Range were light overnight, with some moderate gusts. In the Swan, the Aeneas Ridge station reported average sustained winds of 30 mph with 50 mph gusts. 

These winds followed the arrival of yesterday's (Tuesday) low-density powder. The Swan Range received the most snowfall, with Noisy Basin's weather station reporting 10 inches of snow with very little snow water equivalent (0.7 inches) in 24 hours. The WMR ski area reports 6 inches of new snow, with much lesser totals in the Flathead Range. This type of snow quality is exceptional for the Flathead and is on par with Southwest Montana's coined description of "cold smoke."

Given the low-density snowfall, sluffing in sheltered locations is to be expected. This problem is confined to steep terrain, generally above 38 degrees, and is most dangerous in long-running gullies or lengthy sustained pitches. The cold temperatures will keep the new snow cohesionless, inhibiting bonding in places where this snow rests on wind-hardened surface snow.

We don't anticipate the light amount of water weight from yesterday's storm to awaken buried weak layers. However, a triggered wind slab may have the potential to step down and initiate a Persistent Slab avalanche, particularly in the Swan Range, where these weak layers appear to be most problematic.

Come one, come all! Flathead Avalanche Friends Fest, a four-day festival from Feb 8-11, has a full schedule with mini-clinics, a keynote speaker, après, and a Big-A$$ Raffle. A little something for everyone. We hope you can join us to celebrate our community, learn about snow, and support our safety mission. Learn more here.

Motorized Level 1 - Instructed by Eric Knoff and Six Points Avalanche Education from Tuesday, February 7, 2023, to Thursday, February 9, 2023. More details are here.

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