Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
2 · Mässig
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Kernpunkte

Terrain-specific evaluation of avalanche likelihood and consequences remains key at upper elevations. On some  leeward slopes, recently-formed slabs of drifted snow remain sensitive to the weight of a person or snowmachine. Snowfall forecast for Tuesday and Wednesday may bring more widespread hazards.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    In the Swan Range, gusty winds have drifted snow at upper elevations, creating thin slabs that can be dangerous above terrain traps. These slabs aren't widespread, so you'll need to do slope-specific evaluation to avoid surprises. Thicker drifts can produce larger avalanches that are harder to escape or more likley to bury you. Thinner slabs can pack a surprisng punch if they carry you into or over a terrain trap, like trees, gullies, or cliffs. 

    The slabs aren't likely to be growing with the light winds forecast for today. If, however, you see blowing snow and active loading, take a step back and plan B to sheltered terrain.

    (12/14/2024)

    Cracking in recently drifted snow is a sign that you've found a slab that may be sensitive to your weight on steep terrain.

Avalanche Discussion

This morning, I'm paying attention to two competing trends. The first are the observations that include few or no signs of instability (Swan Range; southern Whitefish Range; northern Whitefish Range). The second is the incremental loading on the layer of surface hoar and facets buried 12/7. 

The last reported slab avalanches in the region look to have occurred on Dec. 7 or 8 (here, here, here and here), when a storm rapidly buried a layer of surface hoar and facets. Since then, we've had only occasional reports ( 3 of 42 obs) of collapses. Most people report large column tests that don't propagate, or only do so with moderate or hard force. Good to go, right? 

Maybe not. That's where the second trend comes in. Flurries and weak storms are gradually building a thicker slab above the 12/7 layer, and as this layer consolidates, it becomes stiffer and more likely to propagate a collapse. It doesn't appear we've crossed that threshold yet. But a few inches of snow Sunday, and at upper elevations, some wind-blown snow, is pushing some slopes closer to it. 

The takeaway is to continue to evaluate the specific terrain you're considering riding. Dig down and look for a distinct grey stripe. Propagating or collapsing snowpack tests on this layer are a sign you've found a slope where the slab is overloading the 12/7 layer. So are shooting cracks and whumpfing collapses. If you don't get those, pick lines that avoid mid slope convexities and aren't above terrain traps, in case conditions are different lower on the slope than your evaluation. 

Downloaded the app yet? You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can doublecheck danger ratings and travel advice on the drive or in the backcountry. And submit an obs while driving home. 

Are you looking for avalanche education opportunities? Check out our calendar for upcoming events. Tonight, Monday, December 16, there is an Avalanche Awareness Class at Bias Brewing.

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