Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
1 · Faible
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

Recently formed slabs of wind-drifted snow are strengthening but could still be triggered by a rider. Cracking in the surface snow directs you to seek out softer, safer snow in sheltered locations. Although unlikely, triggering a slide on a buried weak layer remains a threat, especially in areas with a thin snowpack.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    After a lengthy absence, the wind returned to the Flathead Thursday night and remained elevated Friday. Observations noted thin slabs of wind-drifted snow and fresh cornice growth, both reactive and non-reactive to the rider's weight in locations open to the west and southwest winds. 

    Wind-drifted snow will be near ridgelines, saddles, and prominent terrain features. Swirling winds may have mixed down to the surface, affecting large open valley floors or even blown uphill. Slopes susceptible to cross-loading may hold thicker deposits on the sidewalls of gullies and possibly further down-slope than expected. 

    An etched or rippled surface, dunes, pillow-like features, and stiff snow are evidence of the wind.  Cracking in the surface snow indicates you have found a sensitive slab. Terrain sheltered from the wind will hold a higher-quality product with generally safer conditions. 

    (1/10/2025)

    Friday's elevated wind speeds formed thin surface slabs and cornices. Weighting a pair of skis produced shooting cracks, a sign of a sensitive slab. This red flag directs you to seek out lower-angle or sheltered terrain. 

    Photo: Mark Dundas

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    Although unlikely, there remains a chance that a rider could trigger a large destructive avalanche on a buried weak layer. A layer of surface hoar and a faceted crust are found 1-4 feet below the surface and are responsible for natural avalanches during post-Christmas snowstorms. Fortunately, these weak layers are strengthening and showing fewer signs of instability in snowpack tests. However, we can not write them off just yet.

    Slopes where these layers are closer to the surface are most susceptible to triggering. These include windy locations and rocky terrain where the snow depth is variable. Convex rollovers are another prime location where a rider could get in trouble.

    Choose slopes with a deep, uniform snowpack free of convexities. Default to slopes with clean runouts without surface obstacles or terrain traps that would magnify the consequences of a slide. If unsure of what is beneath the snow surface, choose lower-angle terrain for a safer experience.

    (1/4/2025)

    The flank of a large slab avalanche. The crown is located several hundred feet above, out of view. This slide failed in facets resting on the 12/18 crust buried around 80cm below the snow surface.

    Photo: Mark Dundas

Avalanche Discussion

Wind speeds have decreased at all stations following the short-lived wind event Thursday night - Friday. Stations in the Swan, Flathead Range, and southern Glacier Park became eerily quiet compared to the Whitefish Range, where speeds remained slightly elevated. Today, expect light winds remaining below the threshold for transporting snow in most locations. An example of calm conditions is exhibited by our windiest station, Aeneas Ridge, which averaged a mere 5 mph over the past 24 hours! 

The lack of recent wind transport is allowing slabs to strengthen. We assume the thickest and largest features are found on open slopes above the tree line, although we have yet to receive an observation from that terrain. We list the likelihood of triggering a wind slab at upper elevations as possible but have dropped the likelihood to unlikely at mid-elevations. 

On Saturday, observers in the Flathead Range generally noted wind-affected snow in open areas that were not reactive to their weight (Observation 1, Observation 2). A party in Cascadilla found a couple of generations of wind slabs in cross-loaded gullies with one pillow cracked 10 feet in front of their skis. Another observer in the Flathead noted the wind moved up a north slope, leaving wind-affected snow and fair-quality riding.  Sheltered slopes held good quality settled snow, but we did receive two reports of a new rime crust that formed Friday night and dampened their day. Rob was in the Whitefish Range, surprised by the lack of wind-drifted snow in a typically drifted area. We did not receive any new information from the Swan Range where 1.7 inches of SWE has been recorded over the past four days. An observation on Friday confirmed a new rime crust to 6400 feet. 

Education opportunities: Check out our calendar for this season's classes here.

January 23 and 25: Motorized Introduction to Avalanches

January 25: Human Powered Partner Rescue - REFRESH

 

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