Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Thu
Alpin
1 · Faible
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering loose snow avalanches will be today's primary avalanche concern. At upper elevations, these will mostly involve dry snow on very steep, shaded slopes. If skies are mostly clear, you can also trigger wet snow avalanches on sunny, mid-elevation slopes.  Avoid terrain where loose snow slides can carry you into a terrain trap.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1–1.5

    If skies are mostly clear, the surface snow on steep, sunny slopes may become wet and prone to sliding on the crust below it today.  Rollerballs, pinwheels and treebombs are clues that these conditions are developing. Wet snow sluffs will be relatively harmless unless they gouge below the crust or entrain more than 8 inches of snow. If temperatures warm more than forecast, this hazard could develop on isolated upper elevation slopes as well.

    (12/22/2023)

    Small fields of rollerballs were noted on steep mid-elevation slopes. These likely developed during the rain on 12/20.

    Photo: Mark Dundas

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1–1.5

    On most slopes, the 4-6 inches of snow that fell before Christmas has had ample time to settle.  On very steep slopes, it’s still possible to trigger sluffs of loose dry snow. These will run on crusts that formed on 12/22.  

    If you feel the tug of steep terrain on a shaded aspect, double-check your runout and ability to manage sluffs.  While slow moving and not involving much snow, sluffs can be serious if they drag a person or machine into or over rocks or trees.

    (12/25/2023)

    Sluffing in steep, shaded terrain.  Sluffs are easily managed on open slopes such as this.  In more constricted terrain the consequences become more hazardous.

Avalanche Discussion

Return of the inversion!  Our weather pattern right now is a far cry from overnight dumps and faces full of powder. You will see lower valley stratus decks again today and balmy temperatures if you climb in elevation up to 6,000 feet.  Above there, expect near-freezing temperatures, dry snow and quality skiing and riding.

High pressure generally brings stable avalanche conditions along with it.  Today is a classic example of skiing/riding what is in front of you.  If you’re traveling into the upper elevations above 6,500 feet, you may be lured into shaded aspects to find the driest snow.  This snow fell several days ago and on most slopes, has had enough time to settle and bond with the old snow below.  Steep terrain, above 40 degrees, could still have some surface sluffing.

If the snow that is in front of you starts to stick to your skins or fall out of the trees, you are most likely at mid elevations and starting to deal with a wet loose avalanche problem.  Temperatures at these elevations will be close to freezing today and just a few degrees of warm up could change the snow surface dramatically.  Pay attention to your location on slopes and move to more pleasant and stable terrain if you find yourself in this situation.

Winds have generally been calm and the availability of snow for transport is limited due to thin melt freeze crusts or settlement.  However, high peaks and ridgelines could still have isolated thin wind slabs.  Think about the consequence of the terrain below you before you drop onto a leeward aspect.  

And don’t forget to listen to the snowpack that you travel on.  Yesterday (Tuesday), I felt a collapse on a north aspect in the Whitefish Range at 7,300 feet.  Probing and digging confirmed a shallow snowpack and a thin 12/7 crust with a weak layer of facets/surface hoar below it.  Propagating results in our stability test (ECTP8 and ECTP23) showed that in very isolated terrain weakness may still lurk.

While we're in an extended period of mostly stable weather and avalanche conditions, you can still get into trouble. The steep terrain that's attractive in these conditions can dramatically magnify the consequences of even small avalanches. A good reminder of this problem is an avalanche accident that occurred on Mt. Brown on Saturday. Dec. 23. One member of a climbing team was overrun by debris from a large loose snow avalanche and injured. The party was aware of the seriousness of the terrain they entered and monitoring conditions. Even so, they were surprised by a sudden natural avalanche cycle. Low Danger doesn't equal no danger.

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