Boletín de aludes

Flathead Range & Glacier NP

Flathead Avalanche Center
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Peligro de aludes

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

Lo esencial

You can still trigger a large avalanche in both wind-affected and sheltered terrain. Small slides could cause a larger, more destructive avalanche on a buried weak layer. Manage your sluff on steep slopes with loose surface snow, and opt for low-angle terrain if the snow cracks and collapses under your feet or machine. 

Problemas de aludes

  • Wind Slabs

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

    Today, winds will shift to southwesterly and redistribute abundant recent snowfall into sensitive slabs at the upper elevation. Previous northeasterly winds have drifted snow in unusual locations at all elevations, including on or near the valley floor. These features may form on surfaces of low-density snow or facets atop hard slabs, resulting in avalanches that can break easily and wider than expected. 

    You've found a slab if the snow surface becomes stiffer than you've been traveling through. Cracks shooting out from your skis, board, or machine indicate instability. Look for ripples, dunes, and fresh cornices, signs the wind has been at work. 

    It is still possible to trigger a slab avalanche in wind-sheltered terrain. Natural or triggered avalanches at the surface have the potential to initiate the larger Persistent Slab avalanche described below. 

     

    (1/18/2024)

    Wind-driffted snow was confined to ridgelines at this location. 

    Photo: Cam Johnson

  • Loose Dry

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

    Loose Dry avalanches are likely on steep, sheltered slopes with eight or more inches of recent snow. Sluffs are difficult to escape on continuously steep slopes and in confined gullies. They are particularly dangerous if they carry you through exposed hazards, over a cliff, or into a terrain trap where even small amounts of snow can pile high above you. Choose slopes that allow you to manage your sluff and do not ski or ride directly above your partner. 

    (12/24/2023)

    Easily triggered but harmless sluffs triggered while sidehilling in the northern Whitefish Range.

    Photo: blase reardon

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    You can still trigger a hard slab on weak layers buried 1-4+ feet deep. Avalanches failing on these layers occurred during each of the last two storms; however, the distribution of this problem remains unclear.

    You may or may not observe obvious warning signs like snowpack cracking or collapsing before triggering a slide. Avalanches could be triggered remotely, from gentler terrain below, above, or to the sides of steep slopes. Persistent Slab avalanches can break wider and higher on slopes than expected. The only way to identify this problem is to dig into the snow. Look for weak snow resting on a crust formed in late December.

    Small slides in the new snow can step down to these layers and initiate a large avalanche. 

    This problem may exist on isolated, open, unvegetated slopes at low elevations, like steep cut banks and road cuts.

    (1/18/2024)

    Crown from a large to very large avalanche that failed naturally. Likely failed overnight on 1/17. 

    Photo: Cam Johnson

Avalanche Discussion

It’s been a good fight, but only one can prevail in the cage match between warm and cold air masses. As we enter the weekend, an incoming warm front will choke out any remaining arctic air. Currently, cold air is still entrenched in the Middle Fork and North Forks of the Flathead, where it’s -20 to -10 degrees Fahrenheit, but it will soon be on its way out.  

Probably the biggest winners in this rumble were people who enjoy powder snow. Wednesday’s overrunning event produced 1-2 feet of low-density snowfall throughout the advisory area. Yesterday (Thursday), Cam and I visited the Flathead Range, where we found deep blower snow on all aspects and elevations. We also used great visibility to catalog recent avalanches along the crest. Many small to large (D1-D2) sluffs and soft slabs had run mid-storm.  We also noted several very large (D3) avalanches that had run during the last two weeks. Likewise, BNSF Avalanche Safety reported a widespread soft slab cycle late Wednesday evening in John F Stevens Canyon. 

Although natural activity has tapered off, a rider can still trigger a slab avalanche in wind-affected and sheltered terrain. With new snow and tolerable temperatures, the hype is high to get out of the house and into the mountains. Take a conservative mindset as you return to the slopes.

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