Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
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

Dangerous avalanche conditions exist. Dense slabs of drifted snow have formed on usually windward or sheltered slopes. Where these slabs are more than about 8 inches thick, triggered and natural avalanches will be large enough to bury or injure a person. Shooting cracks are a clear sign of this danger.

The avalanche danger will rise overnight with continued winds and additional snowfall. If accumulations reach or exceed forecast totals, the avalanche danger could reach High Wednesday.

Problemi valanghivi

  • Wind Slabs

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

    Moderate to strong winds are drifting the weekend's snow into dense slabs that will be reactive to the weight of a rider or snowmachine. You can trigger avalanches from below or adjacent slopes, because these slabs are sitting on weak snow. Triggered slides may break surprisingly wide, with fractures connecting across terrain features and involving multiple start zones. Natural avalanches are possible. This hazard exists on usually windward and sheltered slopes, because of atypical wind directions (easterly and northerly instead of westerly and southerly). 

    Winds in this weather pattern tend to have their wicked way with the snow surface on all aspects. That can make it difficult to distinguish wind-packed snow surfaces from dangerous slabs. Be alert for shooting cracks and whumpfing collapses. Where the cracks are about 8 inches or more deep, you've got the potential for large, dangerous avalanches on and below steep slopes. 

    Slabs will continue to thicken today, keeping the danger elevated as the winds whip any new snow around. Avoid traveling under ridges where you see plumes of drifting snow. Expect to find slabs cross-loaded into usually benign terrain at low and mid elevations. 

     

    (2/1/2025)

    Shooting cracks like these are a critical warning sign today. This was triggered deliberately by the weight of a skier and involved the new snow.

    Photo: Mark Dundas

Avalanche Discussion

Moderate to strong winds are drifting the weekend's snow into dense slabs. The snow under these slabs is softer and weaker; it's either lower-density storm snow or weak facets and surface hoar or slick crusts that were buried Friday. That's a dangerous structure.

Your weight on a dense slab can collapse the softer snow below. The buried old snow is weak and relatively uniform, so collapses and fractures can propagate long distances. That makes triggered avalanches more likely to involve enough debris to bury or injure a person. To add to the complexity, winds are sweeping up slopes that are usually sheltered, and toploading or crossloading slopes that are typically scoured. Today's bitter cold temperatures can turn even small mishaps into survival epics. 

The takeaway is that conservative choices and cautious, careful route-finding are critical to staying safe in the mountains today. Avoid traveling on or below steep slopes where you see drifts, windblown debris like tree branches and conifer needles, or blowing snow. Riding conditions may not be great, with machines and boards punching through wind-packed snow into softer snow. 

I expect the avalanche danger to rise overnight as moisture-laden Pacific Air overrides the entrenched Arctic airmass. Think of it as an invisible sumo match. Pacific Sumo will win, probably in tomorrow afternoon's round. In the meantime, expect steady snowfall, with accumulations at valley bottoms and ridgelines similar. Right now, it looks like 6 to 8 inches of new snow by Wednesday morning. The southern half of the forecast region is favored. With continued winds, that may be enough for the avalanche danger to reach High. Be alert for changing and dangerous conditions the next few days.

Regioni coperte