Avalanche forecast

Swan Range

Flathead Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Winds from multiple directions have formed thin slabs in both usual and unusual locations. Cracking in the snow surface directs you to seek out softer snow in sheltered locations. The chance of triggering a large, destructive avalanche on a buried weak layer is declining, though it remains a concern. Choose planar slopes with runouts free of surface obstacles to minimize your chance of injury.

Avalanche problems

  • Wind Slabs

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

    Shifting winds have drifted snow on various aspects, forming thin slabs.  Slightly older features from Friday's easterly wind event will be found in unusual locations. Recent prevailing winds have been light and only affecting the most exposed terrain. 

    A  rippled surface, dunes, and pillow-like features are signs of wind transport. Another clue is denser snow, where your boards or machine do not sink into the surface snow as deeply as they do on surrounding slopes. Cracking beneath you indicates you have located a sensitive slab. Slopes sheltered from the wind will hold softer and safer snow.

    (12/27/2024)

    The crown face of a wind slab triggered by an airblast. It released on a thin layer of graupel and rimed precipitation particles. These are visible as the different toned layer just above the bed surface.

    Photo: blase reardon

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    Although unlikely, you can still trigger a slide on various deeply buried weak layers. Observations confirm weak faceted snow resting on a stout crust from mid-December as the culprit in recent large avalanches. The weak snow from early December has not been as active lately, but it is still an issue where you find a grey stripe in the snowpit wall.  

    These layers are buried deep in the snowpack and subsequently hard to affect. Slopes where a rider could trigger a large, destructive avalanche are those where the snowpack is thinnest and the layers closer to the surface. These include convexities or rollovers, wind-scoured terrain, and slopes peppered with rocks. Choosing descents with runouts free of surface obstacles and terrain traps will aid in case something goes wrong. Defaulting to lower-angle terrain makes sense if you are unsure if these layers are present.

    (1/4/2025)

    The crown of a slab avalanche that failed during the post-Christmas storm cycle. This avalanche failed on a faceted crust 2+ feet below the surface.

    Photo: Mark Dundas

Avalanche Discussion

Friday's cold air intrusion accompanied by north through east winds was generally weak and short-lived, ending early Saturday morning.  These events often affect the Essex to Marias Pass corridor more than other parts of the region, partly due to the broad low profile of the pass that allows cold air to move west. The BNSF avalanche team noted wind slabs at all elevations Saturday, but they were stubborn to ski cutting. They did note one natural D2 wind slab from the recent winds. Observers in the Essex area did not find similar slabs (here and here).

The winds shifted back to the prevailing south through west direction Saturday morning. However, speeds at upper-elevation stations remained generally below the threshold for transporting snow. Saturday, observers noted a rime crust and freezing rain crust capping the low-density surface snow in the Flathead Range. These crusts vary in elevation and thickness and limit the amount of snow available for transport by wind. 

The Persistent Slab remains on the problem list, albeit unlikely. Recent observations of large natural slides failing on buried weak layers in the Swan Range (Image) and the Flathead Range (Image)  confirm triggering a slide on a buried weak layer is a concern.

Avalanche Awareness Class: Monday, January 6, at Great Northern Cycle and Ski at 6:00 p.m. FREE!

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