Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Increased wind speeds the past 48 hours drifted snow into slabs up to a foot thick at upper elevations. Wind-drifting snow, dune-shaped drifts, and textured surfaces are all signs to keep searching for slopes sheltered from the wind. Generally safe avalanche conditions exist below 6500 feet.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    On Monday, a rider found shooting cracks and touchy cornices in the northern Whitefish Range. Wind speeds since then continued to drift snow into a more cohesive slab. Slabs of drifted snow may range from 6 inches to a foot thick, which would be enough to knock a human off their feet. Wind slabs are more common on the downwind side of ridges and cross-loaded gullies. Terrain on the windward side, or terrain sheltered from the wind are safer options for managing this problem.

    (1/23/2023)

    Shooting cracks in wind drifted snow. 

    Photo: Sara B

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–2

    Weak layers of facets and surface hoar exist roughly 1 to 2 feet below the surface. These layers are proving unreactive at the moment, but should still be taken into consideration. Slopes most likely to harbor these weak layers with a thick enough slab are ones above 6500 feet and previously loaded by the wind. Relatively safer options for riding in steep terrain exist below 6500 feet.

    (1/21/2023)

    This small, but potentially consequential avalanche was triggered remotely by a snowbiker. The rest of the slope cracked but did not slide.

Avalanche Discussion

For the past three days, remote weather stations in all ranges were at speeds capable of transporting snow. The question is, where was there enough snow to transport it into a slab?

Generally, riders found anywhere from 2 to 6 inches of snow above crusts at the middle elevation band (5000-6500 ft). Ultimately, it is not a lot of snow to form slabs large enough to be a concern. You may find some small and isolated pockets of wind-drifted snow at those elevations. The exception is the Swan Range, where more snow fell, and wind speeds averaged 15 to 18 mph for all three days. Expect to find slabs of drifted snow at middle and upper elevations there.

Above 6500 feet, more snow fell, and crusts are thinner or nonexistent. This will give the wind more fuel to form slabs. Slabs of drifted snow may be thicker and larger the higher you climb. These drifts likely rest on weak layers of facets and surface hoar, which can produce a dangerously large avalanche.

There is a trick to dancing around wind slabs with a persistent slab problem of buried surface hoar. Typically, the travel advice for managing wind slabs is to turn to terrain sheltered from the wind. However, terrain sheltered from the wind can spell trouble, especially in the Swan Range. Managing our slope angle and the terrain above us is the only way to effectively avoid this problem.

Regions covered