Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Remotely triggered avalanches large enough to bury a person happened yesterday (Sunday). These occurred on a northeast-facing slope above 6500 feet. Weak layers lurk below the surface on shaded aspects and are prime for human triggering in areas where winds built thicker slabs. You are less likely to trigger a slab avalanche on slopes that face south through west.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Slabs of drifted snow failing on a weak layer of surface hoar are proving to be worrisome and potentially dangerous in the Swan Range. Natural and remotely triggered slab avalanches occurred in the past week. These slabs can wrap around terrain features and can get triggered from a distance, catching you by surprise. Give shaded aspects that face north through east, a wide margin for error today, and allow this layer time to gain strength. You are less likely to trigger a slab avalanche on south through west aspects where winds and sun destroyed this weak layer before it was buried.

    (1/15/2023)

    Crown of a natural avalanche that failed in the last week. 

    Photo: Cam

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Watch for loose wet avalanches and manage your slope angle while traveling through middle elevations en route to higher terrain. Anywhere from 1 to 4 inches of snow fell throughout the forecast area yesterday (Sunday). My party was able to trigger small loose wet slides in the new snow at middle elevations. Wet snow avalanches today will likely be small in size, but problematic if you get caught above a terrain trap.

    (1/14/2023)

    Debris from a loose wet avalanche that piled up on a road cut. 

Avalanche Discussion

The current weather pattern will do little to change avalanche conditions from the past few days. Cloud cover, light wind speeds, and warm temperatures are keeping the snow surface from receiving a hard freeze. This, along with a few inches of new snow, keeps the threat of wet snow avalanches a problem. As daytime temperatures warm the snow surface, wet snow avalanches will be more common above the rain/snow line.

A buried layer of surface hoar is proving to be problematic in the Swan Range. It was buried on January 9th during a storm that favored the Swan Range with 1.2 inches of Snow Water Equivalent (SWE). On January 11th, an observer found it buried under 6 inches of snow and reactive in snowpit tests at 6000 feet. A snowmobiler remotely triggered a large slab avalanche below a ridgeline that same day (observation). Yesterday, my partner and I found evidence of natural slab avalanches that failed sometime in the last week. We remotely triggered two slabs while walking a ridgeline (observation). We were surprised at how sensitive this weak layer remained, a week after its burial. These are clear signs to avoid shaded aspects where winds drifted snow into thicker slabs, and that this problem may stick with us for a while.

Although slabs are failing on a persistent weak layer, we plan to list them as a Wind Slab problem for the next couple of days, as we collect more information. As of right now, we are more concerned about areas where there is enough snow to form a slab above this fragile weak layer. So far, that is where winds have drifted snow.  

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