Boletín de aludes

Flathead Range & Glacier NP

Flathead Avalanche Center
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Peligro de aludes

Fri
Alta montaña
1 · Débil
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

Continue to steer clear of steep rollovers and fresh deposits of drifted snow, which are the exceptions to the mostly stable conditions. You are more likely to find these booby-traps at upper elevations. Reduce the consequences of a low-likelihood event by riding one at a time and keeping your partner in sight.

Problemas de aludes

  • Deep Persistent Slabs

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

    If you're stepping out into consequential terrain at upper elevations, stack the deck in your favor by avoiding steep start zones with convex profiles that are likely to harbor variable snow depths. These slopes are where a person's weight might be able to collapse weak layers near the ground and trigger a very large avalanche. Reduce your exposure to this low-likelihood, high-consequences hazard by traveling quickly under start zones like these when they've been in full sun for awhile. 

    (1/26/2022)

    A well-consolidated snowpack like this isn't where you're likely to trigger a large slab on weak layers near the ground. In this profile, tests did not produce failures or propagation at the Dec. 3 interface about a foot off the ground.

    Photo: Jeff Metsky

Avalanche Discussion

A high-amplitude ridge on the Pacific Coast continues to block storms from reaching our forecast region. Until it breaks down - possibly Monday - we can enjoy blue skies at upper elevations, and a well-consolidated snowpack that contines to stabilize. In these conditions, the slopes where you can still trigger an avalanche are isolated.  

You're most likely to find one of these isolated exceptions at upper elevations on convex slopes where the snowpack is dotted with thin spots. These are often slopes where crosswinds scour away patches of snow, keeping snow depths shallow  and variable. Weak, collapsible snow is more developed and better preserved in the thin spots. The weak layers are also closer to the surface, so they're more easily affected by a person's weight or strain prompted by radiation that warms the surface of the snowpack. Without X-ray glasses, we can't detect the thin spots, or monitor the stresses in the snowpack. So it's best to simply stay off of and out from under start zones like these. 

At mid-elevations, evidence indicates these basal weak layers are strengthening and unlikely to collapse. The snowpack is settling and a weak temperature gradient is strengthening weak layers near the ground. In the past few days, large column tests in the Flathead Range and southern Whitefish Range have produced no propagation on the Dec. 3 interface. One observer did note his small column test produced a sudden failure on a basal weak layer in southern Glacier National Park. We've removed the Deep Persistent Slab avalanche problem from mid-elevations. I'm still wary of windward, sunny slopes where the snowpack is shallow and very soft snow exists near the ground. 

If you're stepping out into consequential terrain in the high peaks , keep in mind that confidence in the forecast diminishes above 8000 feet. We've had few observations from that terrain this season, and it's where the rain-snow line hovered early season. Tuesday's winds were stronger at that elevation, and more likely to have drifted recent snow.

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