Bulletin d’avalanche

Whitefish Range

Flathead Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

While the snowfall has tapered off, you can still trigger slabs that break a foot or more deep, in the new and recent snow. On isolated slopes, it's still possible to trigger slides that break deeper, on old weak layers. Moderately-angled slopes with runouts free from terrain traps offer the best riding today. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2.5

    You can trigger large avalanches that break 1 to 2 feet deep within the new snow or on storm interfaces, as demonstrated by the weekend's series of human-triggered and natural avalanches. The slabs will be getting denser and stiffer as the storm snow consolidates. That means they'll break wider, push you around, and be harder to escape. 

    Avoid steep slopes above things things that are harder than your body - trees and rocks - or that can lead to deep burials - gullies and roadbeds. Avoid steep slopes altogether if you see shooting cracks or hear whumpfing collapses. 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

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    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.

    (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. 

Downloaded the app yet? 

You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can doublecheck danger ratings and travel advice on the drive to the trailhead or in the backcountry. 

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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