Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
1 · Low
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous conditions develop Saturday. You can trigger avalanches on steep slopes with continuous snow coverage. Upside-down storm snow and dense, wind-drifted snow will form slabs thick enough to bury you. Simple terrain with slope angles of 30 degrees or less is the smartest place to ride. Watch for steep terrain above you as you ride or skin on roads and trails.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    Slabs of new and drifted snow are developing on top of soft, weak snow. Under that, a freezing rain crust can act as a sliding surface. Strong southwest wind will make new slabs thicker on leeward slopes. It’s best to avoid slopes steeper than about 30 degrees where more than 8 inches of new snow has accumulated. By the afternoon, slabs could be thick enough for triggered avalanches to bury you. Cracks that shoot ahead of you mean that slabs are sensitive to your weight. Natural avalanches are a warning to avoid roads and trails with steep slopes above.

    (12/10/2021)

    A freezing rain crust 6 inches below the surface failed under the weight of a skier. This layer also failed in Extended Column Tests - ECTP11. SE aspect at 6000 feet.

    Photo: Dundas

Avalanche Discussion

If the weather forecast holds true, we could see up to an inch of new water and 10+ inches of new snow throughout the day. Climbing temperatures could make the new snow upside-down. 

The old surface consisted of wind-affected snow in exposed areas, and soft dry snow above a freezing rain crust in sheltered terrain (Whitefish Range, Swan Range). On Friday, Mark had snowpack tests fail on a thin crust in the Apgar Range. I had similar results around Essex on Thursday. The rain crust is stout and supportable in the Swan and Whitefish Ranges. So, new upside-down storm snow and dense wind-packed snow will fall onto low density, weak surfaces. A crust underneath can act as a fracture plane or a sliding surface. 

Deeper in the snowpack, tough crusts surround layers of weak sugary snow above the ground. Though snow levels have finally reached the valley floors, we have limited coverage below 5,000 feet. At middle elevations, early-season obstacles still poke through the surface. These may limit the start zones and runouts of smaller avalanches. They’ll also act as strainers and increase the consequences of taking a ride.

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