Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can still trigger a large and potentially deadly avalanche on weak snow buried deep in the snowpack. Reduce your risk by choosing planar or concave slopes with a deep snowpack. Limit your travel above terrain traps like cliffs, gullies, or exposed rocks and trees. If the surface snow is wet, move off of, and out from under, steep slopes.  

Problemi valanghivi

  • Persistent Slabs

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

    It is still possible for a rider to trigger a large avalanche that breaks 1 to 4 feet deep on steep slopes. Audible collapses were observed in all three zones during the past week and as recently as yesterday (Wednesday). Whumpfing collapses are a clear sign that buried weak layers remain sensitive to the weight of a person or machine. The problematic structure - weak facets over a hard crust - appears most developed on slopes facing east through south to west and areas close to the Continental Divide. At low elevations, this hazard exists on roadcuts and other steep slopes with continuous snow cover. 

    The most reliable way to reduce your exposure to this hazard is by staying off of and out from under steep slopes. In the absence of clear signs of instability—like recent avalanches, or collapses—do your due diligence by digging into the snow and looking for faceted, “sugary” snow near a crust 1 to 4 feet below the surface. Riding a slope where you find this layer includes the risk of triggering a potentially deadly slide. 

    (1/24/2024)

    Observing the crown of a natural D2 slab avalanche.  This slab failed on weak snow above the 12/22 crust and likely ran Sunday 1/21.

  • Loose Wet

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

    Low-elevation weather stations have reported temperatures above freezing since Sunday (4 days). Stations at middle elevations have cycled above and below freezing during this time. Observations this week have featured all the hallmarks of wet snow in these elevation bands: trees shedding snow, roller balls, and natural wet loose avalanches, some large enough to bury a human. Dense debris can make even small slides difficult to escape, especially on very steep slopes or in confined gullies where debris can pick up momentum.  Move to less steep terrain if you find wet snow surfaces.  Many slopes at low elevations have likely been worked over by previous wet loose activity and are less likely to slide. 

    (1/24/2024)

    The two wet debris piles are old and the one closer occured today (1/24/24). 

    Photo: Cam Johnson

Avalanche Discussion

"Are we there yet?" [There being an unreactive persistent slab problem.]

 "No, not quite..."

Yesterday (Wednesday), A team from FAC traveled to the central Whitefish Range to de-rime the Link Mountain weather station. However, we quickly reprioritized when we encountered a recent avalanche and a booming collapse. Weak snow above the 12/22 crust was the culprit in both instances. This “bulls eye” data indicates that we’re not yet free and clear of the lingering persistent slab problem.

The largest collapse we encountered was on a southeast aspect at middle elevation.  Interestingly, when we dug a pit less than 100 feet away on an adjacent northeast slope, we found a much deeper snow pack and a less developed weak layer.  Also of note, we triggered this collapse just several steps after rerouting our uptrack away from a convex roll-over near the top of a slope. The collapse propagated a crack across the same convexity. Our takeaway:  it is still critical to choose ascents and descents that limit exposure on slopes where the weak and potentially unstable structure exists. 

Winds have generally been unimpressive during the first half of the week and will remain light and southwesterly. Aeneas Ridge in the Swan Range, however, is a notable exception; it's averaging over 20 mph. If you are traveling at upper elevations in an area favored by recent snow and wind, continue to evaluate terrain carefully. Look for signs of wind affected snow like a scalloped surface or dune-shaped feature along ridges saddles and other prominent terrain features. Find a less steep slope if wind-drifted snow cracks around your feet or machine. A small surface slide may have the potential to cause a larger, more destructive avalanche on a buried weak layer.

Regioni coperte