Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 7 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering a large avalanche on a buried weak layer remains our primary concern. Avoid triggering a large avalanche by selecting slopes with a hard, supportable crust. Choose lower-angle slopes if you are seeking out soft snow on northerly aspects.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    A well-preserved buried weak layer exists in the upper snowpack. It is buried within the top foot in areas sheltered from the wind and about 2 feet deep on wind-loaded slopes. This weak layer is responsible for both human-triggered and natural slab avalanches last week.

    Be especially wary of slopes that are typically shaded by the sun, where no crust exists at or just below the surface. These slopes are the most likely places to trigger a large avalanche. You can reduce your chances of triggering a large avalanche by riding on slopes with a supportable crust. Another option is to simply choose low-angle terrain.

    Large natural slab avalanche near Great Northern. This occurred on a SE aspect at 7200 feet. It likely ran sometime between 2/4 and 2/6.

Avalanche Discussion

A storm system favored the southern portion of the advisory area. Noisy Basin in the Swan Range grabbed .6 inches of precipitation. At 6000 feet, this precipitation amounted to only 2 inches of settled snow. I’d expect more snow higher up. Our snow camera further south at 5875’ near Swan Lake recorded 4 inches of snow over the past 24 hours. Moss Peak Snotel, even further south and outside of the Advisory in the Missions, picked up just shy of a foot of new snow since yesterday morning. Your best luck may be to head south if you are chasing powder today.

A weak layer of surface hoar above a smooth crust that formed in mid-January is the primary concern in the snowpack. In the Whitefish and Flathead Ranges, I’d expect to find this weak layer buried within the top foot of snow in sheltered areas. Handpits are an easy way to identify the weak layer because it is buried so shallow. As you travel further south in the Swan Range, this weak layer is getting buried deeper in the snow due to new snow and wind-drifted snow. Uncertainty grows as this weak layer gets buried deeper. Signs of instability may become less frequent, and the size of avalanches will increase. Given the history of remotely triggered avalanches and natural avalanches on this weak layer, I’d suggest giving terrain that harbors it a wide margin for error. Those slopes are shaded aspects near and above 6500 feet. 

Last week's warm temperatures and solar input cooked sunny slopes. Snowpits at the end of the heat wave showed wet snow down to the weak layer. Since the warming event, temperatures have dropped and froze the upper snowpack, locking it in place. Triggering an avalanche is unlikely on slopes with a hard, supportable crust.

Regioni coperte