Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous conditions have developed in the Swan and Flathead ranges, thanks to copious amounts of new snow. You can trigger large slabs that break 1 to 2 feet deep in the new snow that involve dangerous amounts of debris. Conditions will remain dangerous as more snow accumulates today, and could spike to HIGH DANGER if winds pick up. Avoid riding on or below steep slopes, particularly if you see blowing snow above you. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    You are likely to trigger large avalanches that break 1 to 2 feet deep within the new snow or on storm interfaces. Natural avalanches may also release. The potential size of triggered and natural avalanches will grow as more snow accumulates. If winds pick up, the likelihood of avalanches will spike, and the danger could reach high. 

    Avoid riding on or below steep slopes, particularly if you feel wind speeds increase or see blowing snow above you. On a snowmachine, you can find deep, playful riding in the trees. On a board or skies, choose terrain that's sheltered from the wind and not steep enough to slide. Shooting cracks, whumpfing collapses, and recent avalanches are clear signs of danger. Slabs near ridgelines and on slopes that collect wind-blown snow may be stiffer and more sensitive to the weight of a rider or snowmachine. 

    Crown of a skier-triggered soft slab in the Canyon Creek area, just outside the boundary of WMR.

    Photo: Cam Johnson

  • Persistent Slabs

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

    It's still possible to trigger avalanches that break well below the recent snow, in old weak layers  buried earlier this month. These can be released by debris from avalanches involving the new snow, or by a rider or snowmachine on steep, convex slopes. Any slide that breaks on these layers will involve dangerous amounts of debris and very difficult to escape. 

    The terrain most likely to harbor this lingering danger has variable snow depths - and thus many potential trigger points - and a convex profile. Avoid being on or below terrain with these characteristics. This hazard is probably most widespread at upper elevations, in terrain that's scoured and drifted by winds. In the Swan Range, reports of the buried weak layers have been concentrated on the east side of the zone, above Hungry Horse Dam.

    (12/27/2024)

    The crown of a slab avalanche is visible on Little Dog Mountain north of Marias Pass. This may have failed during the 12/17-12/18 storm. 

    Photo: Mark Dundas

Avalanche Discussion

My uncertainty about today's forecast for the Swan and Flathead ranges is about as high as it gets. That's partly because a power outage cut off the data stream from many weather stations at 8 pm last night. It's also because conditions are highly variable across the forecast region and could change rapidly in the next 24 hours, particularly in the Swan Range. The takeaway - safe riding today requires a very cautious and conservative approach in the backcountry, regardless of the danger rating.

I don't have the same uncertainty about the Whitefish Range forecast. Snowfall has tapered off there. We've had a series of rider-triggered slabs in the WMR sidecountry, including two near-misses (here and here) and one accident (we are waiting for confirmation of details before publishing info). All have involved the storm snow; we have no reports of slides breaking deeper, on weak layers buried in early and mid December.

Below are some of the today's knowns and unknowns for the Swan and Flathead Ranges:

  • Known: Lots of new snow, particularly in the Swan Range. It appears that Noisy Basin and Six Mile picked up a foot of snow overnight, at least 15 inches in the past 24 hours, and over 2 feet since Christmas. Those snow totals are enough to put the danger at the edge of High.
  • Known: Winds have been light at upper elevations for most of the past three days. 
  • Known: A forecast for continued snow in the Swan Range, where another foot or more could accumulate. It looks like less in the Flathead Range.
  • Unknowns: Snowfall totals in the Flathead Range and Glacier National Park. I suspect less than the Swan Range, though not by much. Tunnel Ridge has recorded more than 2 feet since Dec. 26 before the data got cut off last night.
  • Unknown: Triggered and natural avalanche activity in the Swan and Flathead zones. Let us know what you're seeing out there, please.

Based on the low wind speeds the past few days and in the forecast, Cam and I are keeping the danger at Considerable in the Swan and Flathead zones today. I expect the danger to rise rapidly if winds start moving snow. Or, to be more dangerous than we've forecast if winds have already been drifting snow and stiffening slabs. 

Keep in mind that there's lots of snow to entrain, and any triggered or natural avalanche may run further than you expect or involve surprising amounts of debris. Choose conservative objectives, have an assessment mindset, and be ready to step back if you see conditions that are surprising or changing rapidly. 

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Events and Education:

Want to start your New Year on the right foot? Sign up for a Partner Rescue Clinic for motorized Riders on January 4. Check out our calendar for other upcoming events. 

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