Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Thu
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Fresh snow and wind may form sentive drifts along ridges and in open bowls. Steer away from etched snow surfaces or dune-shaped features. You can still trigger a large avalanche on buried weak layers where the snowpack is not capped by a hard crust.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–2.5

    February's Atmospheric River and warming produced widespread avalanches on buried weak layers. The threat of triggering slabs that break 2 to 3 feet deep lingers on steep, shaded slopes where weak layers were not wiped out by recent avalanches or capped by a thick and supportable crust.  Keep in mind that slopes harboring the softest riding conditions are where you are most likely to encounter this problem. 

    Weak layers may not give obvious signs of instability before avalanching. Dig below the surface to look for layers of buried surface hoar, facets, and faceted crusts before traveling on or under steep slopes. Sudden collapses or propagation in column tests are prompts to seek out lower-angled and less complex terrain.

    (3/1/2025)

    The crown of a large avalanche that released on 3/1 shortly after noon. The slab likely failed on the January Drought Layer.

    Photo: Tyler Kitch

Avalanche Discussion

Buried weak layers were delivered a one-two punch during the second half of February:

  1. Jab from the left: An Atmospheric River hit NW Montana with rain, snowfall, and wind resulting in a natura cycle of large slab avalanches. This loading was particularly effective on shaded and wind-loaded slopes.
  2. Cross with the right: Warming temperatures and sunshine last weekend caused widespread and large loose wet activity especially on solar aspects. There were also some slab and glide avalanches in the mix.

As temperatures moderate, I’m tempted say weak layers are down for the count. However, I have a couple qualms that the fight isn’t over yet:

  • Observations from shaded slopes above 6000’ have found a mostly dry snowpack with only a thin melt-freeze crust at the surface.
  • Snowpack tests on these slopes continue to produce some unstable results.

You should be curious what’s below your feet or machine anywhere the snowpack isn’t capped by a thick and supportable melt-freeze crust. Take a moment to dig in and answer this question. If you find a weak layer in the top 3 to 4 feet of the snowpack (and especially if you get unstable test results) I would consider moving to lower angle terrain on the off chance these layers get up off that mat and start swinging.

Cornices and glide cracks weakened during the recent warming. Limit your time below these hazards. Many low-elevation sites haven’t had a decent refreeze. Expect to find unsupportable isothermal snow that will make travel difficult.  

Regioni coperte