Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Warm weather today may exacerbate a familiar set of avalanche hazards. Deeply buried weak layers may be more reactive with rising temperatures. Cornice fall can be the trigger for a destructive slab avalanche. Two tactics can reduce your exposure to these problems. Stick to low-angled slopes with a supportable snow surface, and pick routes that keep you out from under cornices and glide cracks.

Avalanche problems

  • Persistent Slabs

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

    Weak layers formed in January sit below 2 to 6 feet of firm snow. They may be more reactive during warming periods. Stick to slopes less than 35 degrees where supportable crusts are conspicuously absent, on north- and east-facing slopes above about 5,500 feet. Avoid slopes near rocky outcrops, with variable snow cover, or with cornices overhead. Cornice fall can be the trigger that sets off a big avalanche. Expose only one person at a time and keep your partners in sight.

    (3/11/2021) A recent Persistent Slab avalanche possibly triggered by a cornice fall on Mt Cameahwait in the Flathead Range. Recent warming contributed to cornice failure.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Observers have noted cracks and holes opening up near the roots of sagging cornices.  Some of these overhanging masses fell in John Stevens Canyon last week. These broad visors of snow can be just the bomb needed to trigger a destructive hard slab avalanche. They are also hazards in their own right. Stay out from underneath of them, and well back from the edge, as the sun heats ridgelines throughout the day.

    (3/15/2021) Big Cornices

  • Glide Cracks

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

    What looks like brown frowns are glide cracks. The entire snowpack is slumping and slowly sliding down the hill on smooth ground underneath - like bear grass or bedrock. They give a rumpled look to the snow surface down slope. They can fail all at once resulting in very large and dangerous avalanches. That’s more likely to happen when sun and warming temperatures lubricate the bed surface with fresh meltwater. Cracks are scattered on sunny aspects throughout the region, though outliers exist. Mark reported a glide crack on a northeast aspect yesterday in the Flathead Range. Avoid traveling on slopes beneath these large cracks and wrinkles in the snow.

    (3/15/2021) Very Large Recent Glide Avalanche

Avalanche Discussion

After a night in which temperatures above 6,000 feet never dipped below freezing, today will be the warmest of the week. Freezing levels will reach well into upper elevations. Cloud cover increases Thursday afternoon. Though wet loose avalanches on sunny slopes have largely run their course, there are a few inches of loose dry snow on shady aspects that could become wet and sluff if the greenhouse effect takes hold.

A few small loose wet avalanches and roller balls slushed their way down sunny slopes in the Swan and Flathead Ranges on the 16th.

Large to very large glide, wet loose, and hard slab avalanches ran on the 14th and 15th - on the hottest days of a warming trend, after nights with no refreez. A few glide avalanches failed on slopes without previously reported cracks, which highlights the unpredictability of the problem.

Observers have noted gaps and holes opening up behind sagging cornices over the past week. A skier remotely triggered a large cornice fall on the 12th.

Midwinter weak layers sit 2 to 6 feet deep beneath hard slabs on all aspects. They may be difficult to trigger where thick, supportable crusts are locking up the snowpack. North and east-facing slopes above about 5,500 feet in the Flathead Range and Glacier Park seem to be missing a surface crust. Unusually warm temperatures can make buried weak layers more reactive. There’s a lot of uncertainty about where old problem layers remain sensitive. A cornice bomb might be just the kind of thing that could release a large, destructive avalanche

Regions covered