Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist last year abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

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.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    New snow and increasing winds make it possible to find cohesive slabs of drifted snow on leeward slopes at middle and upper elevations. Southwest winds may thicken slabs throughout the day particularly near the Continental Divide. 

    Look for signs of wind-affected snow along exposed ridges, cross-loaded gullies or bowls, and downwind from prominent terrain features. Rippled snow surfaces and dune-shaped features are visual cues of wind-affected snow. Cracking around your feet or machine are signs of unstable snow that should direct you to less steep or more sheltered terrain. Slabs 8+ inches thick will be difficult to manage.  Recognize that slab thickness can vary significantly across a slope. 

    (2/26/2025)

    A well-developed cornice line on a mid-elevation forested ridgeline. A small soft slab that was triggered from wind-blown snow is visible beneath the cornice.

    Photo: Mark Dundas

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    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. 

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