Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Sun
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

Human-triggered avalanches have occurred each of the last two days. Recent avalanches, cracking snow surfaces, and collapsing are all signs that you can still trigger large slides in wind-drifted snow or deeper down on buried weak layers.  Choose slopes where a slide will not rake you through obstacles like trees, rocks, or cliffs. When in doubt, stick to lower slope angles.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–3

    Large (D2) avalanches ran naturally during Wednesday's storm.  These slides occurred as new and wind-drifted snow overloaded a weak layer of surface hoar or facets buried 1.5-2.5 feet deep. Give weak layers time to adjust to new loads.

    • These layers can be triggered remotely from attached low-angle terrain.  
    • Audible collapses indicate that you have found a buried weak layer and should signal you to move to less steep terrain.  
    • Buried weak layers have been mostly found on shaded slopes (NW through N to SE).

    (12/9/2024)

    Crown profile on a northeast aspect at 6500 feet. This avalanche failed on surface hoar. Similar avalanches occured during Wednesday's storm.  These layers are still adjusting to new and wind-drifted snow.

    Photo: Cameron Johnson

  • Wind Slabs

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

    Yesterday, a rider in southern Glacier National Park accidentally triggered a large avalanche on a slope cross-loaded by recent winds. Fortunately, they were able to ride off the slab before getting caught. 

    • Recognize wind-affect surfaces by their scalloped texture or dune-shaped features.
    • Look for these signs downwind from ridges, saddles, and other prominent terrain features.
    • Due to intense winds, drifts can be found further downslope than is typical. 
    • Slabs could be firm enough to support your weight but might break above you and wider than expected.

    You can manage this problem by choosing slopes with less than 8 inches of recent or wind-drifted snow. Recognize that slab thickness can vary significantly across a slope. 

    Crown from a large avalanche that was accidentally triggered by a rider in southern GNP.  

Avalanche Discussion

Wednesday’s storm was dynamic, leaving us variable snow surfaces and complex avalanche conditions. We continue to receive reports of natural avalanches that slid during the storm, both in the new snow and on buried weak layers. We also received reports of human-triggered avalanches during the storm and each day since. 

The latest close call occurred on Elk Mountain in southern Glacier National Park. This avalanche occurred on a convex and cross-loaded southerly slope. This piece of terrain is an excellent example of the potential consequences of a slide, as the runout is punctuated by trauma-inducing trees (Photo 1, Photo 2). To increase your margins for safety, choose slopes where the runout is free from obstacles.

Clearing skies yesterday allowed temperatures to climb faster and higher than anticipated and initiated wet loose activity. Many mid- and upper-elevation sites are still above freezing this morning.  Firm surfaces from this week’s rain, wind, and warming will limit the distribution and intensity of wet loose action today. I would expect wet snow to be more of a nuisance than a hazard. However, be prepared to move off and out from under steep sunny slopes if you find see fresh rollerballs and pinwheels. 

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 or in the backcountry. If you’ve experienced any glitches using the app, please email [email protected]

Are you looking for avalanche education opportunities? Check out our calendar for upcoming events. A Partner Rescue Clinic for motorized Riders on January 4 would be a great way to start the new year.  

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