Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

On isolated slopes at upper elevations, a weak snowpack structure still exists. On some of these slopes, you may still be able to trigger an avalanche that breaks 1 to 2 feet deep on old, weak snow. Elsewhere, the biggest hazards to you or your machine are rocks, stumps, logs, and brush.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    Isolated wind-sheltered and shaded terrain above about 7000 feet harbor a weak snowpack. Either avoid steep, consequential slopes that fit this description, or test them with dropped cornices or large column tests. Cracking, triggered slides, or propagation in tests are clear signs you've found a slope where your weight or the weight of your machine can trigger an avalanche. 

    (12/17/2023) A structure that shuold prompt you to think twice. Test pit result ECTP27 on buried 5mm surface hoar 45 cm down. Photo: David Kerner

Avalanche Discussion

A below-average snowpack and poor travel conditions didn't deter riders from the backcountry this past weekend. Thanks to the dozen people who submitted observations. We heard from people who made it to high summits in the Flathead Range, others who overnighted at cabins or bivouaced on ridges, and motorized riders in a Level 1 course.  A lot of miles walked in boots with boards on backs. A lot of miles ridden dodging obstacles that can damage a machine. Determined. 

Most observations described a weak, shallow  snowpack marked by melt-freeze crusts and in many cases, a well-preserved layer of surface hoar (12/1). This layer is capped by a melt-freeze crust several inches thick. When isolated in tests, it still produces propagation with medium or hard force. Slopes where the overlying melt-freeze crust isn't as robust may still be sensitive to the weight of a person or machine. And getting caught in any slide will likely have disproportionately severe consequences, because of the shallow snowpack and numerous hard things a person getting tumbled downhill could - will - hit. So we're continuing to list a Persistent Slab avalanche hazard at upper elevations. 

None of the reports described other signs of instability, however. The chances of triggering a slide on the 12/1 surface hoar, or weak snow near the ground, are low but not zero. The variability between slopes means you'll have to dig and test to get relevent info for decisions to commit to steep slopes. If you dig, be alert for a layer of large, intact surface hoar capped by a thin melt-freeze crust, particularly if tests propagate or collapse on that layer. Dropped cornices that produce shooting cracks or pull out slabs are an obvious sign that you've found one of the isolated slopes that are dangerous.

Regioni coperte