Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Tue
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Non aggiornato — questo bollettino è scaduto last year. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The hazard of triggering avalanches that break on deeply-buried weak layers lingers. Triggered and natural wet snow avalanches will become more likely as crusts that formed overnight break down. Slopes below open glide cracks remain hazardous.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    The primary avalanche concern remains triggering slabs that break 2 to 3 feet deep on weak layers buried at the end of January. Natural avalanches have failed on these layers almost every day of the past week. Some resulted from new and drifted snow during the Atmospheric River; wet loose avalanches and falling cornices triggered more during the subsequent warm spell. Riders continue to report whumpfing collapses.

    Be wary of steep slopes that haven't avalanched recently. If you want to keep things simple, avoid riding on or under these slopes. If you're willing to accept more risk, dig down before committing and look for layers of buried surface hoar or facets near crusts. If these propagate, pop, or drop in column tests, you've found a Persistent Slab avalanche structure with the potential for triggered slides. Whumpfing collapses are audible signs of the same thing. 

    These slides can be triggered by falling chunks of cornice and debris running downslope from wet snow slides. Plan your travel so you can get home with minimal time below corniced ridges and steep, southerly start zones.

     

     

     

    (3/2/2025) Wide crowns on the east face of Mount Grant. Triggering avalanches like these remains possible today. Photo: Paul Fotter

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2.5

    The wet snow hazard will rise on slopes where frozen crusts break down. This process will start earliest and progress fastest on steep, mid-elevation slopes that face into the sun. You'll know it's happening if you or your machine start to sink more than a few inches into wet snow. 

    With overnight refreezes and cloud cover today, I don't expect this hazard to be nearly as widespread as it has been the past few days. Still, mild temperatures and radiation filtering through the clouds will produce enough meltwater that triggered wet snow avalanches remain possible. At low elevastions, this hazard is isolated, despite often unsupportable snow. However, slides that run down to these elevations will likely gouge to the ground, making them more destructive. Keep an eye on slopes above you and minimize travel below steep, southerly start zones.

    Surface slides could trigger a larger slide on buried weak layers, as described in our Persistent Slab problem.

     

    (3/1/2025)

    A large wet snow avalanche that released on a westerly slope late Saturday (3/1). The debris covered the groomed snowmobile trail above upper Whitefish Lake. A similar slide Sunday buried the groomed trail in Canyon Creek.

  • Glide Cracks

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Several more glide cracks failed Sunday, with new cracks also reported. These cracks are most widespread on solar aspects at mid-elevations. On the west side of the Swan Range, there are now at least visible 28 cracks. 

    The chances of these cracks failing are lower today, thanks to an overnight refreeze and cloudy skies. Gravity, however, hasn't eased, and the snow below these cracks continues to glide and creep, albeit at slower rates. Take a good look at slopes above you, and avoid traveling under open cracks with rumpled snow cover below them. 

    (3/2/2025) Slopes below glide cracks remain hazardous. This crack failed about 90 minutes after this image was taken (Sunday about 5 PM). 

Avalanche Discussion

Sunday saw yet more large wet snow avalanches and glide cracks releasing. Wet snow slides buried the groomed trail in Canyon Creek in at least one spot, after slides late Saturday buried the groomed snowmobile trail above upper Whitefish Lake. We've also had reports of wet snow avalanches triggering slabs that broke several feet deep on weak layers buried at the end of January. Debris from some of these slides has gouged to the ground where the snowpack was shallow. Glide cracks failed on Half Moon, just east of WMR, late Saturday. Other glide failures were reported in the Swan Range both Saturday and Sunday. 

The likelihood of avalanches like these has diminished today. Stations above 6000 feet recorded 3 to 10 hours of sub freezing temperatures overnight, and today's forecast calls for highs near freezing. Cloud cover will limit the amount of incoming solar radiation on slopes facing east to south through west. With less meltwater produced at the snow surface, near-surface snow is unlikely to get saturated and less water will percolate to mid-pack weak layers. 

While these hazards are less widespread today, you can still find trouble if you wander onto the wrong slope. You could trigger a hard slab that fails several feet deep , on weak layers that developed during January. Or you could get hit from above by slides like these, wet snow avalanches, or glide cracks. Be alert for overhead hazards and make sure you start for home early enough to be out from under these threats.

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