Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
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

 Winds have drifted snow into fresh slabs on varying aspects above 6500 feet. Steer around dune-shaped drifts on your hunt for soft snow. Recent observations generally describe conditions as “a little more than dust on crust.”

Problemi valanghivi

  • Wind Slabs

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

    Expect to find soft slabs up to 1 foot thick in wind-loaded terrain features at upper elevations. These terrain features include slopes below exposed ridgelines and on the sidewalls of gullies. Varying wind directions over the last few days formed slabs on a variety of aspects. The painted distribution identifies recently formed slabs of drifted snow that will be more sensitive to the weight of a rider. This does not mean it is impossible to trigger an older, and more stubborn Wind Slab on southerly-facing slopes. Look for textured surfaces and dune-shaped drifts for evidence this problem exists. Signs of cracking around your board or machine should steer you to areas sheltered from the wind.

    (12/19/2023)

    Look for signs of drifting, like the one photopgraphed, for areas to avoid. Slabs will be most common near ridgelines and gullies. 

    Photo: guy zoellner

Avalanche Discussion

Roughly 3 to 8 inches of new and recent snow blankets a hard crust throughout the forecast area. Recent signs of unstable snow are limited to new snow problems. Observers have triggered Loose Dry avalanches in steep terrain, while others found small Wind Slabs on exposed slopes. Ski Patrol at Whitefish Mountain Resort triggered Wind Slabs 6 to 10 inches thick with ski cuts and explosives on Sunday. 

Wind directions have shifted from northeast to southwest over the last couple of days. This shift in winds formed two generations of recent slabs. The older, more stubborn slab of drifted snow will be in areas favorable to northeast winds. Observers reported finding slabs on south and west aspects yesterday (Monday). The more recent and more sensitive slab will be on slopes drifted by southwest winds. These may be thinner and smaller in size due to less snow available for transport. To simplify, I’d recommend looking for signs of wind drifting as soon as you find roughly 6 inches of recent snow. This will be more common above 6500 feet in elevation. Slabs should be easy to avoid with visual clues, as described in the Wind Slab problem description.

We removed Persistent Slab as a listed hazard on Monday. You can still find soft facets around a hard crust on many middle and upper-elevation slopes. Recent warm temperatures allowed these facets to gain strength. A supportable crust near the surface also adds strength to the snowpack by reducing the chances of collapsing the weak layer. In steep, high-consequence terrain, it is still worth digging to look for this structure, especially if you don’t find a supportable crust beneath your feet or machine.

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