Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Triggered loose snow avalanches are today's primary avalanche hazard. Whether they involve dry snow or wet snow depends on aspect, elevation, and cloud cover. They can be dangerous if they push you into or over a terrain trap, like tree wells, gullies, or rock bands. On isolated slopes at upper elevations, you can still trigger hard slabs that break 2 to 6 feet deep on old weak layers. Think twice before committing to steep, upper elevation slopes with variable snow depths and convex shapes.

Avalanche problems

  • Loose Dry

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

    The most widespread hazard reported in the past few days has been sluffs of loose, dry snow. As the recent snow settles, these are becoming less likely. Today, I expect them to be confined to slopes steeper than about 40 degrees where the surface snow remains loose and dry. Pick lines with options to let fast-moving sluffs pass you. Avoid confined gullies and slopes above terrain traps.

    (3/23/2021) Loose snow avalanche involving dry snow. These are more dangerous where they can run long distances and entrain more snow.

  • Loose Wet

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

    Triggered sluffs of wet snow can carry you into gullies and other terrain traps. This hazard will most likely be confined to low elevation slopes and steep, mid-elevation slopes that face southeast to west. However, it won't take much sun or greenhousing today for this hazard to spike and spread to upper elevations and shady slopes. Rollerballs fanning down slope from your boards or snowmachine are a clear sign that wet snow avalanche hazards have developed. The dense debris from these slides can be hard to escape, so avoid steep slopes above gullies or that leaves you few options to escape. 

    (3/23/2021) Looking down a south facing slope with an example of a triggered wet, loose slide. This one is harmless; sluffs that gouge deeper and entrain more dense wet snow can be dangerous.

  • Persistent Slabs

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

    Steeper than 35 degrees? Convex or unsupported in shape? Variable snow depths, due to wind scouring and drifting? These are the characteristics of the terrain where a person might still be able to trigger a thick hard slab that breaks on weak snow buried in late January. Chances are low; consequences are high. And the tools for identifying trigger points (x-ray glasses) are unavailable. The more of these factors that exist on a slope, the riskier it is to ride. 

    (3/17/2021) Convex, unsupported, variable snow depths - the kind of terrain where you might still be able to trigger thick hard slabs.

Avalanche Discussion

Spring is apparently the best Winter. Most of the region has seen 1 to 2 feet of new snow since Monday, with little wind. And observations are consistent in describing this recent snow as loose and triggered dry snow sluffs as the most widespread avalanche hazard. Thursday's reports also noted that some wet snow concerns developing below about 5500 feet.

The new snow has settled, so natural loose dry avalanches are becoming unlikely and triggered sluffs will be confined to slopes steeper than about 40 degrees. That could change quickly when and where the recent snow gets direct sun, or direct sun followed by low clouds (greenhousing). Have an exit strategy that allows you to escape to lower-angled, sun-sheltered slopes, and a route home that minimizes your exposure to slopes receiving direct sun. The wet snow problem will be more acute this weekend, as high pressure brings partly-sunny skies and warmer temperatures.

A few isolated but important caveats: I wouldn't disregard the possibility of triggering soft slabs of recent snow on steep slopes, particularly in the Swan Range. While no slabs of this nature have been reported,  the range did see significant snowfall Wednesday night, and the storm snow may consolidate in today's mild temperatures. Use hand pits, test slopes, and slope cuts to look for cohesive layers of near-surface snow. Re-assess your plans if you find them. Winds picked up overnight, so you may find pockets of drifted snow near ridges and summits, and at the top of steep chutes. Small slabs can have outsized consequences in very steep terrain, so find alternatives if you encounter dense snow that cracks or collapses. 

Lastly, great riding can draw us to upper elevation terrain that harbors weak layers buried in late January. Though we don't have a lot of recent information about these layers, they appear to be sintering into the snow above and below them.  Where these are still intact, they are typically buried deeply enough that a person is unlikely to collapse them and start a slide that propagates widely. Shallow spots are likely trigger points, so avoid terrain pock-marked with thin snowcover. The northern Whitefish Range has seen the least snow in the past month, and these layers may generally be closer to the surface there. 

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