Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Lions, tigers, or bears - a range of avalanche hazards will make for dangerous conditions today. You can trigger slabs of drifted snow one to two feet thick, or soft slabs of fresh snow on sheltered slopes. Triggered slides may step down and release larger slabs on weak snow near the ground. Natural avalanches are also possible. Any triggered or natural avalanches will run long distances. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3

    You can trigger freshly-formed slabs of wind-drifted snow that break one to two feet deep and run long distances. Winds during Tuesday's storm remained out of the southwest and west near the crest of the Swan Range, so these slabs exist on easterly and northerly slopes at mid and upper elevations. Winds diminished overnight and veered to the northwest; expect a few small fresh slabs to form on upper elevation south through west slopes today. Natural avalanches that release near ridges will run long distances. Avoid steep slopes with thick drifts of wind-blown snow. Stay out from under steep start zones near ridges. 

    (12/4/2022)

    Plume of wind-blown snow from easterly winds. Swan Crest.

    Photo: FAC

  • Persistent Slabs

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

    New and recent snow are incrementally loading weak layers buried near the ground. Avalanches that break on these layers would involve dangerous amounts of debris, even on seemingly small slopes. The weak layers are probably most reactive to the weight of a person or snowmachine where they're closer to the snow surface - slopes where wind or sun limit how much snow accumulates, or shallow spots around convex rollovers and near ridges. Whumpfing collapses are clear signs that these layers are being overloaded. Because of the potential for triggering these slides from gentler slopes, I'd be very hesitant to ride or climb slopes 30 degrees or steeper, especially those below steeper slopes. 

    (12/6/2022)

    Looking uphill at a soft slab avalanche crown in the Whitefish Range. This slope is steeper than 35 degrees - exactly the kind of terrain to avoid.

    Photo: sarah williams

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    Low-density snow can be surprisingly cohesive, making it possible to trigger slabs of fresh snow one to two feet thick on slopes around 35 degrees. These slabs will be larger and more widespread at mid and upper elevations, where more snow has fallen over the past week. They may exist on isolated slopes at low elevations. Cracking and recent avalanches are clear signs the recent snow has consolidated enough to release as a slab. The most straightforward way to reduce your risk of this hazard is to stay off slopes that are steeper than about 35 degrees. Triggered slabs may produce surprising amounts of debris. On steep slopes where the snow hasn't settled into a cohesive slab, long-running loose snow avalanches may pose a hazard.

Avalanche Discussion

Dangerous avalanche conditions exist today, and bitter cold temperatures can turn small mishaps into survival stories, or worse. Over the past two days, the forecast region has been been a wrestling ring for a sumo match between Pacific and Arctic air masses. As these two giants have pushed each other around, they've left multiple avalanche hazards that vary in distribution between the zones and within different elevation bands in each zone. If you brave today's frigid temperatures, you'll need to be alert for conditions that vary in short distances and may exist in unusual locations. 

The most widespread hazard today will be slabs of drifted snow. Where the winds blew from the typical southwest and west, these will mostly be in the usual spots that collect wind-blown snow. That's mostly the case in the Swan Range and near the crest of the Flathead Range. Where winds increased overnight and veered northerly and easterly, these slabs have formed on unusual slopes. That's the general pattern in the Whitefish Range and Glacier National Park, including the Apgar Range. It's also the case in low-elevation terrain in the Middle Fork, which channels cold air. The winds are forecast to continue at or near threshold speeds today at upper elevations, so expect these slabs to continue to grow and remain reactive today. Any wind slab that releases at the top of a long avalanche path with a steep track will likely run full path, making runouts dangerous. 

While the low-density new snow doesn't contain much water, it nonetheless is incrementally loading weak layers buried in November. While these layer have shown signs aof healing the past week, the new load may be interrupting that process and re-activating these layers. Triggered wind slabs may step down to these layers, making for dangerous amounts of debris. 

The new snow poses a hazard in itself, even where it hasn't been blown by the wind or isn't adding load to basal weak layers. It will be possible to trigger avalanches that break in or at the base of the new snow today, as it settles into soft slabs on slopes sheltered from the wind. Loose snow avalanches can pose a hazard on slopes approaching 40 degrees where the new snow hasn't consolidated. 

 

Training: Now's a great time to hone your companion rescue skills. Transceiver parks are open at Whitefish Mountain Resort, one at the summit and one adjacent to Grey Wolf. Both are accessible to snowmachines. You can get more details about training and education opportunities events on our events calendar.

Observations - Thanks to everyone who's been utilizing our new observation submission page. Try it out and help your community by sharing what you see in the backcountry. The form requires you to fill out the location fields and put a dot on a map. Be as specific or vague as you want. Our new Observation View page highlights signs of instability and allows you to filter by date or zone to pull out reports relevant to your objectives.

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