Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can trigger dense or hard slabs of drifted snow on steep slopes that can be dangerous where they're more than about 8 inches thick or above a terrain trap. Thanks to terrain-channeled winds, these may exist at any elevation and aspect. Stay alert for shooting cracks and whumpfing collapses, which are clear signs the surface slab is sensitive to your weight or the weight of your snowmachine.

Problemi valanghivi

  • Wind Slabs

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

    Look for - and avoid - steep slopes with slabs of wind-blown snow. You might find these at any elevation and on unusual aspects, because wind directions and speeds have been channeled by drainage-scale terrain features. Further muddying the picture is a forecasted shift in wind directions about midday today, which may drift snow from currently sheltered slopes.

    Pay close attention to surface conditions today and spend some energy distinuishing wind-packed snow surfaces from dangerous slabs. Quick hand pits or shallow snow profiles are a good way to determine if a wind-packed surface is capable of producing an avalanche large enough to bury or injure you. Look for dense, hard drifts more than about 8 inches thick. Be alert for shooting cracks and whumpfing collapses. 

    The recently-formed slabs are sitting on softer storm snow from the weekend, or on very weak snow surfaces left by the January dry spell. With this structure, you can trigger slabs from their thinner edges, from below, or from adjacent slopes. Avoid traveling under ridges where you see plumes of drifting snow.  Gullies at low and mid elevations may be crossloaded, making them terrain traps. Hard slabs are not wise choices for slope cuts, because they tend to break above a rider.

     

    (2/1/2025)

    Wind-packed surface snow. Punch through with your hand or ski pole to determine how thick the layer is. Where it's more than about 8 inches thick, you've got the potential for large avalanches on steep slopes.

    Photo: Flathead Avalanche Center

Avalanche Discussion

While I'm confident there are plenty of wind slabs out there this morning, I'm hard pressed to describe where you're most likely to find them. That's because wind directions and speeds have been very terrain specific the past 24 hours. Perenially windy sites like Aeneas Ridge have recorded light winds while other sites at similar elevations show averages in the upper 20s and gusts to 50 mph. And some low elevation sites are also showing strong winds, while nearby sites are nearly calm. The strongest, most consistent winds look to have been in the John F. Stevens Canyon area and southern Whitefish Range, two areas where Arctic air tends to get channeled into strong easterly and northerly winds.

Snow totals from the past 24 hours are underwhelming. The storm has favored the southern half of the region, with 4 to 8 inches of low density snow. The Whitefish Range looks to have picked up only a few inches. The pattern looks to continue today, providing more material for the wind slab machine as winds veer to the west. 

So today, safe travel depends on identifying and avoiding fresh and recently formed slabs that are likely to exist in unusual locations and at any elevation. You may find these cross-loaded into gullies or streambeds at low elevations, or behind mid-slope terrain features. Ridges with cornices on both sides are a sign that winds have loaded usually windward slopes. Dunes and pillows midway up or down a slope are a clue that it's loaded with wind-blown snow. When winds shift to the west midday, new slabs may start forming. 

It may take some creativity and flexibility to sniff out sheltered terrain where the wind hasn't created slabs or difficult riding. In these areas, you may find a foot or more of new and recent snow over the weak snow surfaces buried Friday. Be alert in these areas for cracking, whumfing collapses, and other signs that this snow is sensitive to your weight on steep slopes. 

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