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

Lo esencial

Watch out for small slabs of wind-drifted snow. Dune-shaped drifts and wind-textured snow surfaces are visual clues for areas to steer around. Move to shadier aspects if you feel the warm sun and see the surface snow become wet and rollerball. Although it is unlikely, the consequences for triggering a 2 to 4+ feet thick on shaded aspects remain severe. 

Problemas de aludes

  • Wind Slabs

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

    The most sensitive slabs of drifted snow are those that formed the most recently, from westerly winds. Those that are ripe for triggering should crack around your boards or machine. Thankfully, these slabs should be relatively small. However, you can run into trouble in consequential terrain. Avoid getting caught above cliff bands or thick stands of trees.

    An older generation of slabs developed this weekend. North and east winds wreaked havoc in some areas and left others unscathed. Slabs from that wind event should be unreactive to a person's weight except on isolated slopes. Keep your eyes open for these, since they may be larger in size and more consequential. Look for evidence of drifting in unusual places and utilize small test slopes before committing to larger objectives.

    (3/25/2024)

    Riders outside of WMR used small test slope with safe runout zones to check sensitivity of recently formed wind slabs. 

  • Persistent Slabs

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

    There are no new reports of avalanches failing on weak snow buried 2 to 4+ feet deep in the last week. These layers should be gaining strength and are near a depth where it is difficult for a human to trigger. You are unlikely to trigger a slide where a hard and supportable crust exists just below the surface.

    If you choose to ride where the problem exists, the safest way to manage it is through terrain selection. Choose planar slopes less than 35 degrees. Yes, that does involve breaking out the inclinometer. If you want to step out and accept more risk, stack the odds by avoiding common trigger points. Two that come to mind are convex rollovers and rocky areas where the snowpack appears thin and variable.

    (3/17/2024)

    Identify the type of terrain this avalanche failed in. It is unsupported and rocky terrain. These are common terrain characteristics where natural avalanches failed during the last warming event. 

    Photo: Mark Dundas

Avalanche Discussion

Small Wind Slabs and Wet Loose avalanches are the themes for recent avalanche activity (wet loose photo, wind slab video). This is a breath of fresh air after the last run of very large natural avalanches.

Although slabs of drifted snow exist on all aspects, we highlighted the aspects and elevations where you are most likely to trigger a slab. Westerly winds are creating a more sensitive generation. Older Wind Slabs on north and west-facing slopes are becoming less sensitive to the weight of a person or machine.

Wet Loose avalanche activity is focused on south-facing slopes that receive direct sunlight. Intermittent cloud cover has helped slow the warming. Today, we may see a brief period of sun. If this does happen, Wet Loose avalanches can initiate rapidly this time of year. Thankfully, slides will be small in size and relatively harmless.

The Persistent Slab problem is complex yet simple. Since avalanche activity has shut off, we have to rely on snowpits to determine where the structure remains intact. This is where it is complex. In some areas, the weak layer is noticeably softer and weaker above the crust. In other areas, and even in nearby drainages, the same weak layer is almost non-existent. This spatial variability makes it feel complex.

The travel advice for avoiding the problem is simple. The safest option is to stick to slopes where a hard crust exists beneath the most recent snow. A hard crust reduces the chances of triggering a slab avalanche failing deeper in the snowpack. The aspects where this supportable crust exists are also the same aspects where the weak layer was less developed. When this weak layer was active, many avalanches failed in unsupported and rocky terrain on north-facing slopes. Remain skeptical of these areas.

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