Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Expect dangerous avalanche conditions to develop throughout the day. Warm temperatures and solar radiation will cause wet loose avalanches large enough to bury or injure a person. Avoid south-facing slopes as soon as you see rollerballs or small wet loose avalanches coming from steep, rocky terrain. Keep slope angles less than 35 degrees on shaded slopes where a small storm slab avalanche has the potential to step down to a much larger, persistent slab avalanche.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Sun-baked terrain will produce wet loose avalanches large enough to bury, injure, or kill you. Wet loose avalanches will be more dangerous in areas where 8 or more inches of new snow fell. Sunny weather and warm temperatures will wet this new snow today, causing large avalanches to fail naturally. Rollerballs or pinwheels are signs that conditions are ripe for wet loose avalanches. To reduce your risk of this problem, seek out shaded, northerly-facing slopes. Plan your exit for the day to avoid crossing below south and west-facing avalanche paths.

    (3/20/2021) Large skier triggered wet loose avalanche. East aspect. Essex area.

  • Storm Slabs

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

    On Monday I was able to easily trigger small storm slab avalanches on all aspects. Today, expect slabs to break 4 to 6 inches deep and possibly up to a foot thick if it fails at the new/old snow interface. Utilize small test slopes to assess how the new snow is bonding to itself. If small test slopes prove to be reactive, or if you see cracking in the new snow, stick to slopes less than 35 degrees. If conditions are pointing you towards stepping out into steeper terrain, select terrain that has clean runouts and is free of terrain traps below.

    (3/22/2021) Storm slabs breaking in the new snow. Expect them to be more reactive where they rest on a layer of weak, sugary grains or a slick crust.

  • Persistent Slabs

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

    Although it is unlikely, it is not impossible to trigger a very large hard slab avalanche failing 2 to 6 feet deep on shaded aspects above 6500 feet. One week has passed since the last reported avalanche failing on weak layers that got buried in late January. The destructive size and reactive history of the weak layer is still enough to keep me off slopes where no supportable crust exists. Rocky slopes with thin and variable snow cover are most suspect for triggering. Stick to slopes less than 35 degrees in areas where you do not feel a thick, supportable crust under the new snow.

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

Avalanche Discussion

New snow piled up much deeper than remote weather stations were reporting on Monday. We saw new snow depths reach up to 16 inches by mid-afternoon in the southern Whitefish Range where the Big Mountain station was showing 5 inches. Other reports came in of up to 10 inches of new snow in the Flathead Range. Noisy Basin in the Swan Range picked up a whopping 1.2 inches of snow water equivalent.

You will have to manage two problems with this freshly fallen snow. The first will continue to be storm slabs on all aspects. New snow will slide easily on crusts or weak faceted snow. Manage this by looking for cracking around your machine or skis, and utilize small test slopes with a spotter to see how the new snow is bonding to itself. If you see cracking or are able to easily trigger avalanches on small test slopes, dial back terrain choices and keep slope angles below roughly 35 degrees.

The next developing problem today will be wet loose avalanches. Recent light, fluffy snow will become wet and slide easily on buried crusts. I won’t be surprised to see many large wet loose avalanches failing naturally by the end of the day. Manage this problem by being observant to obvious clues. Rollerballs, snow falling out of trees, point releases from steep rocky areas or snow glopping up on your skis are all signs that the snow is getting wet, and ripe to avalanche. As soon as you see this, hightail it to shaded aspects where the snow should remain cold all day.

There is a lingering concern for a small avalanche, cornice fall, or a human to trigger a large persistent slab avalanche to fail on weak layers buried 2 to 6 feet deep. The best travel advice is to stick to slopes less than 35 degrees above 6500 feet on shaded aspects.

Many large glide cracks exist at mid and upper elevations that may be covered up with freshly fallen snow today. Look closely at surfaces and avoid being under anything that appears to have a horizontal, frown-like depression in the snow. Last week we received reports of numerous glide avalanches that produced impressively large debris piles.

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