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
1 · Débil
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

Bitter cold temperatures are today's primary danger. Plan your day so you can quickly escape to shelter. The cold can also exaggerate the consequences of triggering slabs of drifted snow or sluffs of loose snow. The safest riding today will be on mid-elevation slopes less than 35 degrees that are sheltered from the wind.

Problemas de aludes

  • Wind Slabs

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

    As you climb towards ridgelines and summits, you're more likely to encounter dense slabs of wind-drifted snow.  Likewise, your chances of triggering these increase as slope angles approach or exceed about 35 degrees. Low-density surface snow may mask visual clues to these slabs, so probe or dig down to check for dense snow over softer snow in terrain prone to collecting wind-blown snow: the tops of chutes, leeward slopes below cornices, and cross-loaded gullies.  The western and eastern halves of the forecast region may harbor fresh slabs on opposite sides of the compass.

    (12/23/2021)

    An FAC Forecaster team triggered this small, soft slab of drifted snow on a mid-elevation leeward slope in the southern corner of Glacier National Park.

    Photo: Nelson

  • Loose Dry

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

    On very steep slopes, you can trigger sliffs that run far and entrain enough debris to be dangerous or push you into a terrain trap. Avoid riding above gullies, trees, and cliffs that can magnify the consequences of small slides. Expect this hazard in upper-elevation terrain sheltered from the wind. It can be hard to escape moving debris in confined chutes. 

    (12/14/2021)

    Sluffs, like this one, are possible where cohesionless surface snow pours down steep slopes. The sluff in this picture did not entrain much snow and was harmless in size.

    Photo: Reardon

Avalanche Discussion

Dense slabs of drifted snow at or near the surface? Or loose, unconsolidated snow at the surface, with progressively harder snow below? That distinction will determine today's primary avalanche hazard on steep slopes. Both hazards will be more widespread at upper elevations.

You may find freshly-formed wind slabs on typically leeward slopes in the western half of the region, but further east, they are more likely to lurk on westerly slopes that are usually windward. That's because of a shift in wind directions and speeds overnight. During the day Tuesday, our Aeneas Ridge station recorded westerly winds averaging over 20 mph with gusts to 40, with Hornet in the Whitefish Range also showing moderate winds with strong gusts. However, stations further east, like Tunnel and Snowslip, showed light winds. Wind speeds dropped in the Swan and Whitefish Range once winds shifted to the east and north, but increased closer to the Divide, as Arctic air pushed in from the plains.

The upshot is that you'll need to identify which side of the compass harbors fresh slabs in the area you're riding. Older slabs generated around Christmas may hide under recent, low-density snow in upper-elevation, wind-exposed terrain. To find these, probe or dig, looking for dense or firm snow over softer snow. These may sit on thin weak layers like one reported in the southern Whitefish Range Tuesday. Isolated slabs may exist near places that funnel cold Arctic Air, like the notch in Canyon Creek. 

In terrain without a fresh or lingering Wind Slab avalanche problem, the primary hazard today will be triggering sluffs of loose, dry snow. While most will be small, they can be dangerous if they push you into a terrain trap, like a tree well, or gully. Triggered sluffs will run further and entrain more snow - and thus be more dangerous - on slopes with a continuously steep pitch. Have escape routes so you can move aside and let the debris pass. 

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