Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Managing isolated avalanche hazards will become trickier as you gain elevation. Pay attention to changing snow surfaces, and avoid wind-drifted snow in steep start zones. Before committing to steeper terrain, dig to assess the snowpack structure, looking for hard slabs above deeply buried weak layers.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    You can trigger pockets of drifted snow on leeward and cross-loaded slopes at upper elevations. Most of these are soft and shallow, because there's not been much snow available for transport. They can pose a hazard on the isolated slopes where they're more than about 8 inches thick or above a terrain trap. 

    Look for patches of wind-packed snow top-loaded onto steep start zones near ridges, or cross-loaded into chutes and gullies downslope. They may lure you into trouble because they might be the softest, deepest snow on the surface. Keep in mind that the debris from a small wind slab can trigger larger slabs that break on deeply buried weak layers. 

    (3/10/2025)

    Snow available for transport was minimal, however moderate-to-strong West winds were creating soft slabs along upper elevation ridgeline. These were limited to cracking underfoot. 

    Photo: Michael Reavis

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    On isolated slopes, there's a lingering hazard of triggering a hard slab avalanche that breaks on deeply buried weak layers. These weak layers formed in January, and will be closer to the surface - and easier to collapse - on slopes where scouring and drifting tend to leave variable snow depths. The suspect slopes didn't avalanche recently and aren't capped by a supportable melt-freeze crust. Unsupported slopes above cliffs and convexities are also candidates.

    Digging into the snow and testing the weak layers is the only reliable way to identify whether a Persistent Slab avalanche structure exists in the terrain where you're traveling. You've likely found the structure if your tests produce propagation or sudden collapses. Note that "structure" is different from "stability." The latter is much harder to determine. If the structure exists, assume the slab is sensitive to the weight of a rider or snowmachine.

    Slabs that release on the January weak layers can break surprisingly wide and connect multiple start zones. Falling chunks of cornice can trigger natural avalanches. The most straightforward way to minimize your exposure to this hazard is to stick to low-angled terrain that's not threatened by steeper start zones above.

    (3/10/2025)

    A recent natural hard slab avalanche in the Flathead Range. It was the only one visible, illustrating the isolated distribution of the hazard. 

    Photo: Michael Reavis

Avalanche Discussion

After a dry January, a cold February marked by two very widespread natural avalanche cycles, March is feeling...meh*. Mild temperatures, strong and gusty winds, and snow showers but no storms. The plus side is that the weak layers that developed in January are strengthening and consolidating, while wet snow avalanche problems have diminished. Meanwhile, the wind slab machine hasn't had much fuel (snow available for transport). That leaves us with isolated avalanche hazards, mostly at upper elevations. Yet somewhat complicated travel conditions, because the avalanche hazards overlap in places. 

The most obvious weather factor in the mountains the past few days has been strong winds. These have been blowing from the south, southwest, and west. Without much soft snow that can get blown around, however, there's been limited wind slab development. These will be more widespread as you gain elevation, and in the Flathead Range. 

Lydia and Mike had good visibility in the Flathead Range Monday. They spotted the crown of one large natural avalanche that looked recent - the past few days. It was a hard slab that released on a steep, southeasterly slope at upper elevations. Nothing similar was visible in the multiple drainages around them. That illustrates the isolated distribution of the Persistent Slab avalanche problem. January's buried surface hoar and facets remain intact and retain the potential to propagate a fracture on some slopes. While it's hard to be more specific than that, I remain leery of unsupported and convex slopes, particularly those with variable snow depths. In terrain like this, it would be easier for a person's weight to collapse any preserved weak layers and trigger a slide. Digging and testing the snow can be a good way to assess whether the Persistent Slab avalanche structure exists. To get info you can trust, however, it takes multiple tests in multiple places. Interpret inconsistent results as a "nope."

We've had no reports of recent glide avalanches. It's still worth staying out from under open cracks, because the tug of gravity is constant; the slabs below the cracks are still creeping and gliding downslope. The tally of cracks on the west side of the Swan Range is up to 39. Plenty more have been spotted elsewhere in the region.

*meh as in there's not enough new snow or a distinct enough diurnal melt-freeze cycle to know you're going to find good riding. But it's there. I found perfect corn Saturday, and Lydia and Mike reported good but inconsistent riding Monday. Ya gotta be cagey, and you won't know unless you go.

Curious about recent developments in tele boots and bindings? Check out Telefestivus at Blacktail Ski Area on Saturday, March 22 and Sunday, March 23. In conjunction with the mind-freeing event, Tamarack Brewing will host a fundraiser with a raffle and film for the Friends of the Flathead Avalanche Center from 5 to 8 PM Saturday, March 23. 

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