Bulletin d’avalanche

Swan Range

Flathead Avalanche Center
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Danger d’avalanche

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

Points saillants

If today's storm continues as forecast, expect complex, dangerous avalanche conditions to develop. In areas where more than 8 inches of new and/ or drifted snow has accumulated, avoid riding on or under steep slopes. Large triggered avalanches are likely; natural and remotely-triggered avalanches are possible. Where rain falls on fresh snow, Wet Loose avalanches will be possible. 

Problèmes avalancheux

  • Storm Slabs

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

    New and wind-blown snow will form dense slabs that can be dangerous on or below steep slopes. These slabs will become more widespread and reactive as the day progress. Even in areas that don't receive much new snow, thick slabs may form well below ridgelines, thank to powerful winds at all elevations. 

    While the storm snow poses a serious threat in its own right, it is overloading a hear-surface persistent weak layer on the isolated slopes in the Swan zone where it has survived. This may make for some unpredictable avalanche activity today. You may be able to trigger 1 to 2 foot thicks slabs from below start zones or from adjacent slopes, and fractures may propagate across terrain features and connect multiple start zones. 

    Shooting cracks, whumpfing collapses, and fresh avalanches are clear signs of dangerous conditions. Very large natural avalanches are possible in large avalanche paths with leeward start zones and steep tracks; these could run into mid and low elevation terrain. 

    (4/7/2024)

    Storm slabs, like this one, will become thicker and more sensitive during today's storm.

    Photo: Jeff Metsky

  • Loose Wet

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

    Where rain falls on fresh snow, wet snow avalanches will be possible. These can be dangerous on or below steep slopes with more than about 8 inches of new snow or above terrain traps, where dense debris can make for deeper burials. This hazard will be confined to terrain below the rain/ snow line, which is forecast to be about 5500 feet. Rollerballs fanning down a slope are a bullseye data that this hazard is developing. 

    (4/24/2022)

    Below the rain/snow line (~5500'), Wet Loose avalanches will be possible on steep slopes. 

    Photo: Mark Dundas

Avalanche Discussion

Dangerous avalanche conditions are developing, and with dry and wet snow avalanche problems, backcountry travel will be complex. To keep things simple, we're not listing the Persistent Avalanche problem involving the 12/7 facets and buried surface hoar. That said, the 12/7 persistent weak layer remains a serious concern and complicates travel even more, because avalanches that break on this layer will be larger and may be triggered remotely. Expect to see the Persistent Slab problem make a comeback once the storm ends, and we get a clearer picture of how the layer is reacting to the new snow. 

Conservative, cautious travel conditions are critical in the backcountry today, thanks to the overlapping set of avalanche problems and uncertainty and variability of the 12/7 persistent weak layer. Pay close attention to slope angles and avoid being above terrain traps. Weave around the runouts of steep slopes above you, especially those were you see active wind loading or rollerballs of wet snow. Be alert for changing conditions as the rain line creeps up, wind speeds spike, and new and drifted snow accumulate. Leave yourself an avalanche-proof route home.

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. And submit an obs while driving home. 

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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