Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Tue
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

An Avalanche Warning is in effect. Very dangerous avalanche conditions exist. Avoid being on or under slopes steeper than 30 degrees. Avalanches will run long distances and be large enough to bury and kill a person. New snow, blowing snow, and rain on snow may overload the snow surface and buried weak layers resulting in widespread areas of unstable snow and natural avalanches.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Rapid loading of snow and rain may cause weak layers buried in the snowpack to fail. If triggered, slides will propagate wide distances and be difficult to survive. Avoid being on or under slopes 30 degrees or steeper. Don’t let vegetated slopes give you a false sense of security. These kinds of slopes, especially ones that face north, are most likely to carry weak layers of buried surface hoar. 

    (2/8/2022)

    Very large (D3) avalanche that likely failed on buried persistent weak layers on 2/6 or 2/7. Heavy snowfall and/or rain may overload these same weak layers today. 

    Photo: Alan Davis

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–3

    New snow, wind, and increasing temperatures will form slabs large enough to bury, injure, and kill a person. Expect slabs to grow in size and to become more sensitive to the weight of a person or machine throughout the day. Avoid being on or under slopes steeper than 30 degrees due to the likelihood of natural and human-triggered avalanches. Avalanches will run far distances, especially if dry debris runs far enough to entrain wet snow below. 

    (2/25/2022)

    Accidentally triggered a small slab with a 12" crown on a 35 degree, north-facing slope

    Photo: Mark Dundas

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–3

    Freezing levels are forecasted to climb to roughly 6000 feet, bringing rain into the middle elevation band. Expect wet avalanches to fail naturally and to run far distances. Wet debris is destructive and nothing to tango with. Avoid being on or under steep slopes if you see rain falling out of the sky. 

    Photo taken last year. Expect wet debris to run far distances and in timbered forests. 

Avalanche Discussion

We went from hero to zero in a matter of 12 hours. The past few days, you could ride it if it was white. Today, plan your day to avoid all avalanche terrain. That is being on or under terrain that is 30 degrees or steeper. We’ve been fortunate to have generally safe avalanche conditions recently; now it is time to tune it way back and head to low angled slopes free of overhead hazard.

Remote weather stations show a range of 4 to 10 inches of new snow overnight. Tunnel Ridge in the Flathead Range has picked up 10 inches, with 5 of those inches falling in two hours. The Whitefish Range has picked up 4 to 6 inches of new snow, and the Swan Range is showing less snow but almost an inch of water as of 6 AM. It is uncertain whether this precipitation is falling in the form of rain or snow. Temperatures have already begun to climb to near freezing at many stations around 6000 feet as of 5 AM this morning.

Forecast models show anywhere from 2 to 3 inches of precipitation by Tuesday morning. This may drop 2 feet of snow at upper elevations (above 6500 ft). Temperatures are forecast to climb, creating upside-down storm snow. This recipe can make avalanches more sensitive to triggering. Snow will likely turn to rain late morning or this afternoon at the middle elevation band (5000-6500 ft). Rain on snow is always a wild card and is especially true for the first of the season. Wet avalanches are very likely once the rain begins to wet the surface. We can not rule out the possibility of wet slabs failing if liquid water reaches buried crusts, facets, or surface hoar that exist 1 to 3 feet below the surface.

This type of weather event can suss out any weakness in the snowpack. Rapid loading may awaken buried weak layers in the snowpack and cause avalanches to propagate wide distances and travel further than expected. Today and tomorrow are not the days to be in or near the runouts of large avalanche paths.

Régions couvertes