Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering a large, dangerous avalanche on a buried weak layer remains our primary concern. Choose lower-angled terrain free of rollovers to outsmart this tricky problem. A poor refreeze overnight coupled with today's warm temperatures may develop wet snow hazards. Move to a different aspect if the surface warms up and becomes unsupportable.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    We remain wary of triggering a slide on a weak layer buried 1-2 feet below the surface above a hard, slick crust. This layer appears to be gaining strength and is providing less feedback over time, but this is a tricky problem. Slopes that don't offer clues, such as audible failures (whumphing) or shooting cracks (like the picture accompanying this problem), should not automatically be deemed safe. The same goes for slopes where snowpits don't identify this problem because these weak layers are not everywhere on the hill. Use terrain to avoid triggering a large, dangerous avalanche by choosing slopes less than 30 degrees in steepness free from rollovers.  

    (3/15/2022)

    Guy giving a stomp to an unsupported slope to test buried weak layers. 

    Photo: Blase Reardon

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Friday, observers reported basketball-sized pinwheels and a supportable crust in the morning becoming bottomless mush by the afternoon. A poor refreeze overnight combined with today's warm temperatures may provide a repeat of yesterday. Most of the action will occur in the mid-elevation band, although isolated slopes at upper elevations may also develop wet snow instabilities. Clues that you have overstayed your welcome are crusts breaking down and rollerball activity forming. Stay ahead of this morning's sunshine and move to a different aspect or elevation band if the surface snow becomes wet. Limit your time traveling above terrain traps or in long-running gullies.

    (3/18/2022)

    Wet Loose debris came within 50 feet of reaching the Marion Lake trail. This path slides occasionally and is located near the wilderness boundary sign.

    Photo: Paul Fotter

Avalanche Discussion

A trough of low pressure and associated cold front is forecast to affect our area this evening with several inches of snow, strong winds, and much cooler temperatures. The fast-moving nature of this system should result in only modest amounts of snow. The avalanche danger may increase overnight due to new snow totals and strong, gusty westerly winds. The Swan Range is favored for snow, and if totals meet or exceed forecast amounts, a storm slab problem may develop. If not, expect a wind slab problem to be a concern tomorrow. The Whitefish Range and the Flathead Range may only pick up several inches of snow, but a wind slab problem may be on tap with elevated wind speeds. 

The Persistent Slab problem remains our primary concern. Feedback such as whumphing or collapsing, shooting cracks, and triggered avalanches are becoming much less frequent than we experienced earlier in the week. The buried layer of near-surface facets responsible for a series of triggered and natural slides is slowly gaining strength, but we do not have enough confidence to drop this problem. One week ago today, Saturday, March 12, is when warm overnight temperatures and wind transformed cold, low-density surface snow into a slab. Numerous skier-triggered and natural avalanches were reported last weekend. Tuesday's warm, dense snow initiated several slides on buried weak layers in the southern Whitefish Range. The last recorded Persistent Slab avalanches occurred Wednesday when skiers remotely triggered slides in the southern Whitefish Range and the Flathead Range. The terrain is always the answer when dealing with this type of problem. Continue to choose slopes less than 30 degrees in steepness free of rollovers.

Support the Flathead Valley Ski Education Foundation by attending the screening of Mission: Mt. Mangart. A story of 10th Mountain Division "Ski Troops" in WWII. Saturday, March 19, at the O'Shaughnessy Center in Whitefish. Get your tickets here.

The FAC March intern Megan wrote this week's weekly summary of weather, snowpack, and avalanche conditions. You can find this and the weekly summary video in the Conditions Blog tab. 

Our final Community Chat is next Tuesday, March 22. In these events, Host Sara Boilen debriefs near-misses. This time she turns the attention to a close call she had earlier this season. Sign up for this virtual, free event here.

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