Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

The danger of triggering slabs that fail on weak snow buried deep in the snowpack lingers. You can reduce your exposure to this hazard by sticking to planar or concave slopes with runouts free of rocks, brush, trees, and gullies. Triggering wet snow avalanches remains a hazard on steep slopes where the snow surface hasn't refrozen. 

Problemi valanghivi

  • Loose Wet

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

    After several days of above-freezing air temperatures, you can trigger wet snow avalanches at low and mid elevations. The dense debris can make even small slides difficult to escape. The most dangerous terrain will be very steep slopes where rollerballs released from your skis or machine entrain more snow as they move downhill. If you encounter these conditions, retreat to lower-angled slopes. Or levitate to 7000 feet.

    (1/20/2024) Rollerballs and tree bombs increased by mid afternoon. They're a clear sign of wet snow avalanche danger when they entrain more snow as they move downhill. Photo: Jeff Metsky

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Triggering large avalanches that break 1 to 4 feet deep remains a hazard on steep slopes. The problematic structure - weak facets over a hard crust - appears most developed on slopes facing east through south to west. Audible collapses observed in all three zones the past week indicate this structure remains sensitive to the weight of a person or machine, particularly on slopes where the slab is less than two feet deep. At low elevations, this hazard exists on roadcuts and other steep slopes with continuous snow cover. 

    The most reliable way to reduce your exposure to this hazard is by staying off of and out from under steep slopes. Whumpfing collapses are a clear sign this hazard exists. If you don't hear these, you can dig into the snow and look for faceted, “sugary” snow around a crust 1 to 4 feet below the surface. Riding slopes where you find it means accepting a risk of triggering dangerous slides. 

    (1/20/2024)

    Snowprofile at 5900 feet on SE aspect. It's an example of the Persistent Slab avalanche structure: a thick, hard slab above crusts and weak layers near the ground.

    Photo: Sarah Williams

Avalanche Discussion

Ch-ch-changes. Rain and wild swings in temperature are putting the snowpack in the region through some changes. In the short term, the quality of the riding is suffering. In the long run, the water and heat are reducing the distribution and sensitivity of a Persistent Slab avalanche problem that's a legacy from December. Cam's video below is a quick summary of the problem.

We're not in the clear yet, however, so it remains important to approach terrain cautiously. Evaluating terrain for potential consequences is more reliable than determing stability. Convex rolls - where slopes abruptly turn steeper - are likely trigger points. Runouts with dense alder and brush, cliffs, gullies, or roadbeds can increase your chances of being injured or fully buried. Leeward slopes that collect wind-drifted snow can harbor thin slabs that, once moving, can step down to more deeply buried weak layers. The terrain where you're least exposed to a Persistent Slab avalanche tends to be planar or concave slopes with clean runouts.

You can see the importance of terrain selection in the report on a fatal avalanche accident near Lookout Pass earlier this month. Events like that are devastating for the people and families involved. They can also act as mirrors that show alternate realities for our own habits and decisions. In Stevens Peak accident, the triggered slide failed in a snowpack with similar layers as ours, on a convex slope above a terrain trap. It highlights the importance of readily recognizing potentially dangerous terrain. That's a skill that develops with practice in conditions like we have now. 

Regioni coperte