Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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

As new snow accumulates today, the likelihood and size of triggered and natural soft slab avalanches will rise. Adding to the danger today is the possibility of triggering hard slabs that break deeper in the snowpack. Enjoy the new snow - and moderate temperatures! - by sticking to low angle slopes that aren't below steep start zones or above terrain traps. As the day progresses - and the danger rises - resist the temptation to chance it on consequential terrain. 

Avalanche problems

  • Storm Slabs

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

    Natural and triggered soft slab avalanches will become more likely - and larger - as low-density snow accumulates today. These slabs will be dangerous where they're more than about 8 inches thick or release above terrain traps.  They'll break more easily and wider where winds have preferentially deposited the storm snow. Where the new snow isn't cohesive enough to form slabs, sluffs that entrain scary amounts of snow are possible. 

    Careful and cautious routefinding is the key to enjoying the new snow while reducing your risk of getting caught or buried in an avalanche of new snow today. Stick to ascent routes that keep you off of and out from under steep slopes - those steeper than about 35 degrees. Use an inclinometer to check your work. Pick lines that have runouts free of alder thickets, gullies, and rocks to reduce the potential consequences if your caught. Enter slopes high or from the side, where you can escape or let debris go by if a slope releases. Ride one at a time so you have the best chances of cleaning up surprises or mistakes. Clear signs of increasing danger are cracking in the new snow and fresh avalanches. 

    Cracking in new snow is a sign it's cohesive enough to release as a slab.

    Photo: Cam Johnson

  • Persistent Slabs

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

    Today, it's also possible to trigger thick, dangerous hard slabs that break below the new snow, on buried weak layers near crusts. The nature of this hazard may change as you gain or lose elevation. On some upper elevation slopes, cold temperatures may have degraded crusts that bridged early-season weak layers. We've found the most distinct persistent slab structure on mid-elevation slopes in the southern Whitefish Range and in the Swan Range. We're not clear how widely it's distributed beyond that.  On steep cutbanks and road cuts at low elevations, you may be able to trigger small, thin slabs on weak snow near the ground. 

    The added weight of today's storm snow may increase the sensitivity of these hard slabs. Natural and triggered slides in the new snow may also step down to these deeper failure planes, creating slides that a person is unlikely to survive. This hazard is another reason to avoid being on or under steep slopes today. 

    (1/11/2024)

    This 3-foot fracture line is the deepest part of the avalanche crown just east of the WMR ski resort boundary. This avalanche is out of bounds.

    Photo: Mark Dundas

Avalanche Discussion

Don't be fooled by the fluff today. A forecast for a foot or more of 5% density snow - at tolerable temperatures! - will likely leave lots of people calling in sick to work or putting off promised jobs. However, the avalanche danger will rise as the day progresses and new snow accumulates. Low-density snow can be surprisingly cohesive (because of the large dendritic grains), particularly where the surface is slightly stiffened by the wind. And the fluff is easily entrained, making triggered or natural slides surprisingly dangerous. Ensure you can enjoy the new snow as it piles up this afternoon - and tomorrow, when the sun comes out - by paying careful attention to slope angles, runouts and safe travel practices today.

Also, don't be fooled by the fluff into thinking that avalanches involving new snow are the only hazard today. Lurking below the new snow are stubborn hard slabs that can be triggered by a person on steep slopes. These can release 18 to 40 inches deep on weak snow near crusts or the ground. This hazard exists primarily at mid and upper elevations; it's isolated at lower elevations due to the thin snowpack and very prominent anchors and surface roughness. We've found the structure that's most conducive to human triggering at mid-elevations in the southern Whitefish Range. Evidence that it a similar structure exists in the other zones  includes triggered and remote slides in the Lost Johnny and Six Mile areas of the Swan Range. and John F. Stevens Canyon in the Flathead zone. The uncertainty about the distribution of these weak structures requires snow profiles and tests to determine if it's present where you're riding. But that takes time away from powder riding; stick to low-angled terrain and make the most of your day. 

There's some disagreement in the weather models this morning regarding snow totals. That's common in overrunning events like these. Snow falling at high rates - more than an inch an hour - will make conditions dangerous sooner. 

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