Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

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

Points saillants

Gusty winds could build sensitive drifts on alpine slopes. Cracking around your feet or machine is a sign of unstable snow. Choose slopes sheltered from the wind for safer riding.

An incoming storm may increase the avalanche hazard overnight and into Saturday.

Problèmes avalancheux

  • Wind Slabs

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

    Gusty southwesterly winds have ramped up ahead of the incoming storm.  Fresh snowfall will add some fuel to wind slab formation. Precipitation isn't forecasted to start until late afternoon, however, expect this problem to become more widespread and sensitive if the storm arrives early.

    • Blowing snow points in the direction of wind-loaded slopes.
    • Sensitive drifts may form on typical leeward slopes, downwind from ridges and saddles, or in cross-loaded gullies.
    • Rippled surfaces and dune-shaped features are hallmarks of wind-affected snow.
    • Snow cracking at your feet or machine indicates an unstable slab.

    Simplify your decision-making by choosing slopes that are sheltered from the wind. 

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    The last recorded avalanche failing on weak layers buried 1-4 feet deep occurred during the December 30th storm. Recent stability tests indicate that several layers of facets, faceted-crusts, and surface hoar are unreactive to the wieght of a rider. While it is unlikely you will trigger a large avalanche on buried weak layers, it is not impossible.

    Avoid this problem altogether by choosing low-angle slopes. If you enter steep terrain, steer around common trigger points like convex rollovers or slopes peppered with rocks. Improve the outcome of any misjudgment by traveling one at a time in consequential terrain, and by choosing slopes where a slide will not rake you through exposed obstacles or deposit you in a gully.

    (1/4/2025)

    The crown of a slab avalanche that failed during the post-Christmas storm cycle. This avalanche failed on a faceted crust 2+ feet below the surface.

    Photo: Mark Dundas

Avalanche Discussion

A refresh is on the way. In the meantime, folks have tried to sniff out some decent riding despite various surface crusts. Overall, recent observations have indicated minimal wind loading. An observation from Comeau Pass in Glacier National Park found isolated wind slabs 5 to 6” thick unreactive to the weight of a rider.

Today, I am confident we will have winds capable of transporting snow. However, I am less confident in how much existing snow is willing to blow. The various crusts reported across the advisory area have had a limiting effect on wind slab formation. Slopes not capped with crusts still have abundant snow available for transport.

Where you observe blowing snow, expect today’s danger to reach MODERATE.  In areas where blowing snow is prevented by surface crusts, the danger may remain LOW. If today’s storm arrives earlier than forecasted, expect more widespread and sensitive wind slab formation.

Régions couvertes