Boletín de aludes

Flathead Range & Glacier NP

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 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The avalanche danger will rise with rapid warming throughout the day. Move to shady, lower-angled slopes before roller balls and small sluffs start running from rocky outcrops. Deeply buried weak layers may become more reactive with rising temperatures. Cornice fall can be the trigger for a destructive slab avalanche. Avoid slopes with cornices and glide cracks overhead. Plan to be down and out from under steep terrain before you find yourself sinking into unsupportable snow.

Problemas de aludes

  • Loose Wet

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

    Solar radiation and daytime warming will again increase the chance of wet loose avalanches. To reduce your risk, move to shaded, north-facing slopes before the snow thaws enough that you find yourself ankle-deep in slush. Roller balls and small wet loose avalanches coming from steep rocky areas are warning signs. You’ll have to start and end your day early if you plan to ride on or under steep, sunny slopes.

    (3/16/2021) Roller balls are a precursor to wet loose avalanches.

  • Cornices

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

    Observers have noted cracks and holes opening up near the roots of sagging cornices.  Some of these overhanging masses fell in John Stevens Canyon last week. They can be just the bomb needed to trigger a destructive hard slab avalanche. These broad visors of snow are hazards in their own right. Stay out from underneath them as the sun heats ridgelines throughout the day.

    (3/14/2021) Big Cornice Sagging

  • Persistent Slabs

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

    Weak layers formed in January sit below 2 to 6 feet of firm snow. Triggering one of these layers is becoming increasingly unlikely, but the result would be an unsurvivable avalanche. Stick to slopes less than 35 degrees if you do not feel a supportable crust under your feet. If you choose to step out into steeper terrain, avoid slopes near rocky outcrops, with variable snow cover, or with cornices overhead. Cornice fall can be the trigger that sets off a big avalanche. Expose only one person at a time and keep your partners in sight.

    (3/11/2021) A recent Persistent Slab avalanche possibly triggered by a cornice fall on Mt Cameahwait in the Flathead Range. Recent warming contributed to cornice failure.

Avalanche Discussion

Warm spring weather brings a full spectrum, a rainbow, of avalanche hazards. 

Reports of a few loose wet avalanches and roller balls came yesterday from the Swan and Flathead Ranges. Glide cracks have been expanding, and failing as avalanches, across the region. Observers have also noted cracks and holes opening up behind sagging cornices. The last hard slab avalanches ran in the heat of the afternoon between the 11th and 14th.

Clearing skies overnight allowed temperatures to drop below freezing. They are forecast to rise rapidly by late morning, again thawing surface crusts, trickling melt water into glide cracks, and weakening the roots of cornices. Rocky and vegetated areas will warm first and most.

As the sun beats down on the snowpack the avalanche danger will rise on southerly slopes where the surface crust breaks down. On cold, dry, north-facing terrain there is no supportable crust, meaning you're more likely to affect buried weak layers on those aspects.

Midwinter weak layers sit 2 to 6 feet deep beneath hard slabs on all aspects. They are becoming increasingly difficult to trigger. A cornice bomb might be just the kind of thing that could release a large, destructive avalanche.

Your lucky charm will be to move to shady, lower-angled slopes before it gets too hot. Watch for roller balls and small sluffs running from rocky outcrops. Plan to be down and out from under steep terrain before finding yourself ankle-deep in wet snow. 

Continue to avoid slopes below cornices and glide cracks. These hazards are more obvious, but less predictable.

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