Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Wed
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In sintesi

Warm temperatures and rain on snow will cause wet snow avalanches today. Below roughly 5500 feet, avoid traveling on steep slopes where you feel wet, manky snow, or see rain falling on snow. As you climb higher in elevation, it remains possible to trigger a slab avalanche failing on a weak layer buried 1 to 4 feet below the surface. Feeling the snowpack collapse or seeing recent avalanches are signs to give steep terrain a wide margin for error. 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Wet snow avalanches may grow in size to be large enough to bury a person today. Rollerballs or pinwheels are a precursor to an impending wet loose avalanche problem. Liquid water moving through the snowpack may cause some avalanches to fail as Wet Slabs. Give steep slopes a margin for error where you see rain falling on snow, or if the snow feels wet and gloppy. Wet avalanches are difficult to escape. They will be consequential if caught in terrain that funnels you into trees, rocks, or onto a flat surface where debris piles up deep.

    (1/20/2024)

    Rollerballs were observed in the moist surface snow on Saturday in Kimmerly Basin. These are precursors to a wet loose slide.

  • Persistent Slabs

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

    Weak facets buried above a hard crust continue to show untrustworthy signs. In the last 4 days, audible collapses have occurred in all three forecast zones. This weak layer is proving more problematic on aspects facing west, south, and east in the Whitefish and Swan Ranges. 

    Use conservative terrain management. You may or may not get cracking or collapsing before triggering an avalanche. These slides may be triggered remotely, from gentler terrain below, above, or the sides of steep slopes. Persistent Slab avalanches can break wider and higher on the slopes than expected. The only way to identify this problem is to dig into the snow. Look for faceted “sugary” snow resting above or below a crust 1 to 4 feet below the surface. This weak layer is buried deeper the higher you climb.

    (1/20/2024)

    A Persistent Slab avalanche failing on a road cut. This avalanche was triggered by a snowmobiler. 

Avalanche Discussion

Although the weather in the valley is purely uninspiring, snow is falling higher up, and the riding is pretty good. If you’re heading out today, here is what you may expect as you climb through the elevation bands.

Precipitation is falling as rain in the valley, and I would expect this to continue up to nearly 5500 feet. Rain on snow is a recipe for wet snow avalanches. These may fail as point releases, or as slabs due to an underlying persistent weak layer on a crust. Thick vegetation sticking through the snowpack reduces the areas where this is a problem. The locations to watch out for are steep road cuts, or where you see a steep snowfield that is free of alder and thick trees. The problematic locations are unfortunately the ones that look appealing to ride through. Although I expect most slides to be small, wet-moving debris is difficult to escape and nothing to tango with.

Above the rainline is where you will have to manage the Persistent Slab avalanche problem. Audible collapses and recent avalanches have occurred in the last few days. The culprit is faceted “sugary” snow buried on the 12/22 crust. If you haven’t been in the mountains for a while, you can find this crust at all elevations. The easy way to find this layer is by shoving your pole or probe into the snow and feeling for a crusty, hard layer. If you are on a snowmachine, you could likely find it by spinning your track deep into the snow and looking in the sidewall of the trench you just carved. Feel for weaker snow around a hard crust. The higher you climb, the deeper in the snowpack you have to look.

This facet/crust combination is proving problematic at lower and middle elevations. As you climb higher in elevation, the problem becomes more specific to aspects that face east, south, and west. This is a result of the sunny and warm weather we experienced in the middle of December. When snowfall returned in late December, it sat on the surface and faceted. 

Plan for this weak layer to be on all aspects if your travels take you closer to the divide. John F. Stevens Canyon, Skyland, Marias Pass, and Central Glacier National Park had a significantly shallower and weaker snowpack earlier in the season. Audible collapses and natural avalanches failed there during the past two storms. 

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