Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Another human-triggered slab avalanche occurred in the southern Whitefish Range. Loose snow avalanches may become possible to trigger during the heat of the day on sunny aspects. Triggering an avalanche 2 to 4 feet thick is a low probability, high consequence scenario. Keep it simple by selecting lower-angled slopes.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    A weak layer of facets near the early February Crust is the culprit of many natural and human-triggered avalanches in the last few weeks. The hotspot of avalanche activity occurred on slopes near and above 6500 feet that face NW-NE-E-SE. Continue to exercise caution on slopes that fit that description. If triggered, slabs can break 2 to 4 feet deep and will be difficult to escape. The most conservative option is to stick to lower-angled slopes in areas where the problem exists. Avoid convex rollovers if you decide to enter steeper terrain.

    Warming temperatures and solar radiation may stress weak layers buried in the snowpack. There is a layered cake of crusts and facets on solar aspects that have yet to cause a problem. The safest option is to give steep terrain a wide margin for error, especially during the heat of the day.

    A large Persistent Slab avalanche. This avalanche failed on an east-facing slope above 6500 feet. 

  • Wind Slabs

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

    Two recent human-triggered avalanches involving wind-drifted snow have occurred in the southern Whitefish Range. Wind Slabs range from thin to thick and new to old. The more sensitive of the two is a slab that is roughly a foot thick. Drifted snow should be fairly easy to identify by its dune-shaped appearance. Be wary of cross-loaded terrain features further downslope.

    Wind Slabs have formed on slopes that harbor weak layers buried deep in the snowpack. A small Wind Slab can step down to a more dangerous Persistent Slab avalanche. Avoid this problem by sticking to slopes less than 30 degrees, or by choosing terrain sheltered from the wind.

    (3/6/2024)

    A slab avalanche that was likely triggered by a rider. This avalanche failed on a mid-elevation slope in the southern Whitefish Range. 

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Solar radiation may cause a loose snow avalanche problem. This will likely start as a dry avalanche problem and transition to a wet avalanche problem late in the day. Rollerballs or pinwheels rolling down the hill are signs of an impending Wet Loose problem. Steep, rocky areas hit by the sun are typically the first place to slide. Move to lower-angle terrain or shaded aspects IF you see signs of warming.

    (2/6/2024)

    Rocky slopes getting hit by the sun are typically the first to slide. These are good terrain features to keep an eye on during the heat of the day. 

    Photo: Sarah for Beth Steele

Avalanche Discussion

The southern Whitefish Range has been the focal point for recent human-triggered slab avalanches. Avalanches are failing up to a foot thick on slopes that face east and southeast. FAC will visit these sites soon to gather more snowpack information. 

The effects of solar radiation are growing as we work our way towards spring. Freezing levels are forecasted to climb to roughly 4500 feet. This will likely increase the chances of triggering loose snow avalanches. Thankfully, loose snow avalanche problems caused by solar radiation are typically easy to manage. Signs like rollerballs, snow falling out of trees, and gloppy snow are indicators of wet snow. 

Warming temperatures and solar radiation can increase the likelihood of triggering a slab avalanche. These environmental factors lead to rapid settlement and increased creep rates in the snowpack. This stresses weak layers and can cause them to fail. We have a few different facet/crusts on solar aspects, and a facet/crust responsible for several near-misses and accidents. The safest bet is to give steep terrain a wide margin for error.

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