Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

We issued an Avalanche Warning in all zones of our advisory area. Dangerous avalanche conditions will continue during a period of prolonged warming. Avoid being on or under steep slopes above 5000 feet.

Avalanche problems

  • Persistent Slabs

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

    Buried weak layers above an early February crust continue to lurk in our snowpack. They may have been the failure layer for large avalanches yesterday (Friday) and earlier in the week. This weekend's warm weather may tip the scales and result in further avalanche activity. Fracture lines breaking 2-4 feet below the surface will likely be an unsurvivable consequence of these slides.

    You're most likely to trigger an avalanche in steep, rocky terrain on shady slopes. However, southeast aspects in some locations have weak layers and the same problematic structure capable of producing a destructive avalanche. Signs of instability, such as cracking or collapsing, may not be present before the slope you are on slides. Avoid avalanche terrain above 6500 feet and avoid being on or under steep slopes below 5000 feet.

    (3/15/2024)

    Several hard slab avalanches ran naturally between 7500'-8500' on SW aspects. Possibly triggered by loose wet.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2

    Overnight temperatures stayed above freezing at many mid- and upper-elevation stations, and today’s temperatures will be unseasonably warm. On Friday, observers reported rollerballs and loose snow slides on sunny aspects. Today, wet snow concerns will become more widespread and destructive, and they may include shaded aspects that currently hold dry snow. 

    Pinwheels or rollerballs indicate the snow surface is softening, and loose snow avalanches may soon follow. Avoid exposing yourself to this problem in terrain with overhead hazards and avoid traveling above terrain traps, where debris can pile up deep, and in long-running gullies, where escape may be difficult.

    (3/15/2024)

    Several hundred feet of the popular Skook skin track was covered in rollerballs from the March 14 warming. 

    Photo: Mark Dundas

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Impressive southwest winds built large cornices along alpine ridgelines in late February/early March. Intense warming this weekend may weaken these features. A failing cornice can send large blocks of snow trundling downhill, potentially triggering a destructive avalanche. 

    The nature of this problem is highly unpredictable and should warrant your respect. Give these whales a wide berth above and below a corniced ridgeline to reduce your risk. Don’t get surprised by a cornice breaking further back than expected.

    (3/7/2024)

    Cornices like these will begin to weaken, crack, and fall due to warming temperatures.  Do not linger on or under slopes with cornice looming overhead. Give them a wide berth as you navigate ridgelines. 

Avalanche Discussion

Ready or not, the heat is on for this weekend. We have issued an Avalanche Warning for the Swan Range, the Whitefish Range, the Flathead Range, and parts of Glacier National Park from 6 am today through 6 am tomorrow (Sunday). Remote weather stations have recorded above-freezing temperatures since yesterday, creating a lack of refreezing overnight. Heat and radiation destabilize thick, hard slabs, weaken cornices, and create widespread areas of wet surface snow.

We are most concerned about hard slab avalanches failing on buried weak layers. This Persistent Slab problem is unpredictable, and the consequences of getting caught in this type of slide are deadly. Observations from yesterday (Friday) included the BNSF Avalanche Safety Team’s report of 3 large slab avalanches observed from Highway 2. FAC Forecaster Cam observed a D2.5 hard slab avalanche on a northwest aspect of Great Northern. Outside of our forecast region, Rob, FAC Forecaster, viewed several large slab avalanches on the west, southwest, and south aspects of the Swan Crest.  These slides likely failed in the late afternoon yesterday. 

Natural and triggered avalanches involving wet surface snow are very likely on both sunny and shady slopes. We expect widespread wet loose activity today. Additionally, this heat wave will weaken ridgeline cornices and increase the likelihood of them unexpectedly breaking and subsequently triggering large to very large avalanches on the slopes below.  Planning an early exit and choosing low-angle terrain are ways to manage your risk in the face of uncertainty. If you observe avalanche activity, let us know what you are seeing by submitting an observation.

Regions covered