Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

In sintesi

Give avalanche-prone terrain a wide margin for error today, especially as you climb in elevation. Avalanches in the new snow may trigger a thicker, more dangerous avalanche. Safe options for riding are on slopes 30 degrees or less. Avoid dawdling in the runouts of large avalanche paths. 

Problemi valanghivi

  • Persistent Slabs

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

    New snow and wind are loading the same slopes that produced Large (D2) and Very Large (D3) naturals last week. A small avalanche may step down to weak layers buried 2 to 4+ feet deep, causing an unsurvivable slide. The safest option for riding is to give steep slopes a wide margin for error today. Choose simple terrain away from the runouts of large avalanche paths. 

    Another faceted crust buried 1 to 2 feet down is the culprit for human-triggered avalanches in the Whitefish Range, and is found in the Flathead and Swan Ranges. Avalanche activity on this layer is more focused on south and east aspects. 

    (3/9/2024)

    A crown of a hard slab avalanche on the north-northeast aspect of a prominent sub-peak directly southeast of Great Northern Mountain at 7400 feet. This may have failed in a layer of facets above the early February crust.

    Photo: Ernesta McIntosh

  • Wind Slabs

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

     Give wind-loaded terrain a wide margin today in areas favored by recent snowfall. Slabs will be thicker and more dangerous along ridge crests and where winds funnel through terrain features. Visual clues of a Wind Slab are dune-shaped drifts and textured surfaces. Shooting cracks are indicators the slab is ripe for triggering in steep terrain.

    It may be possible to trigger a slab avalanche in terrain sheltered from the wind that received more than 8 inches of recent snow. Recent snow may rest on recently formed weak layers. Avalanches failing at the new/old snow interface may break wider than you expect.  

    (2/27/2024)

    A shooting crack is an indicator of unstable snow. These are common in areas where 8 or more inches of snow falls, or is transported by wind. Signs like this should direct you toward lower-angled terrain. 

    Photo: Jeff Metsky

Avalanche Discussion

Storm totals are starting to tally up at remote weather stations. In the past 48 hours, Noisy Basin in the Swan Range picked up .7 inches of Snow Water Equivalent (SWE), Stahl in the northern Whitefish Range picked up 1.2 inches of SWE, and Flattop in central Glacier National Park picked up 1.4 inches SWE. Tunnel Ridge in the Flathead Range gained 10 inches of settled snow since the start of the storm. The driver is the southwest winds that accompanied this precipitation. Winds turned out gusts 40 to 50 mph at remote weather stations. A few more inches and increased winds will thicken recently formed slabs.

There are a couple of different faceted crusts to keep an eye on. The first one you will see in the snowpack is 1 to 2 feet below the surface. Reported avalanche activity on this layer is more common in the Whitefish Range. The second layer is the one responsible for producing the largest avalanches. It is faceted snow above the early February crust buried 2 to 4+ feet deep. The Flathead Range and Glacier National Park are the hotspots for reported avalanche activity failing at this interface.

Weak snow above the early February crust has a bad reputation throughout the northwest. It extends north into Canada, south to Missoula, and west to Washington. Unfortunately, this interface is the culprit of close calls, accidents, and fatalities. This history continues to be the topic of conversation within the forecast team. 

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