Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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

The riding is excellent, but there remains the possibility that you could trigger a slide in the recent storm snow. This will become more likely if you encounter fresh drifts of wind-blown snow. Cracking at the surface or denser-feeling snow directs you to seek out lower-angle slopes.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    The post-Christmas storms were responsible for rider-triggered and natural avalanches. Cool temperatures and light winds limited widespread slab formation, with many observations reporting cohesionless surface snow.  However, many recent slides occurred in a very soft slab that offered quality riding.

    Locations receiving wind strong enough to transport snow will likely develop slabs of wind-drifted snow. It won't take much of an uptick in speed for these features to build, as snow available for transport is plentiful. Look for blowing snow and signs that the wind has been at work, such as dunes and pillow-like features. These should be confined to slopes near ridgetop elevations.

    The surface may develop into a cohesive slab in locations sheltered from the wind as the new snow settles. The snow may feel denser and crack under your or your machine's weight. If in doubt, default to lower-angle terrain for a safer experience.

    Very steep slopes harboring cohesionless snow could sluff from the weight of a rider. These will be most troublesome in large terrain or long-running gullies. Practice sluff management and limit time spent above terrain traps.

     

    (12/28/2024)

    Crown of a skier-triggered soft slab in the Canyon Creek area, just outside the boundary of WMR.

  • Persistent Slabs

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

    Several layers of facets, faceted crusts, or surface hoar are found in the top several feet of the snowpack. The likelihood of triggering a slab avalanche on one of these weak layers is decreasing but not out of the question. The recent storm snow has added stress to these layers but is also strengthening them from the overlying weight. Warm temperatures before Christmas were helpful in the strengthening process. In some locations, they are buried to a depth that a rider or snowmachine may not impact.

    The most likely spot you could trigger a slide would be where the weak layer is closer to the surface, such as wind-scoured locations, convex rollovers, slopes peppered with rocks, or a thin area on the edge of a slab. Debris from the storm slab problem described above could trigger a slide on a weak layer, resulting in a large, destructive slide.

    (12/30/2024)

    A rider triggered avalanche that failed on facets buried in mid-December.

    Photo: Cam Johnson

Avalanche Discussion

Post-storm observations emphasize dry snow, limited wind effects, and excellent riding conditions. The lack of wind at upper elevations for this length of time is nearly unfathomable. The wind station that often reports the highest wind speeds of any station in the Flathead is on Aeneas Ridge in the Swan Range. Rob and Cam visited the station yesterday (Wednesday) to knock rime and snow off of it. They noted that the calm to light winds produced little to no drifting, and windward slopes have a remarkable amount of unconsolidated snow available for transport.

On Wednesday, a rider noted a large soft slab avalanche just east of Peter’s Ridge on the east side of the Swan (Observation). This slide was estimated to be 500 yards wide and 2 to 4 feet deep and occurred at 5800 feet. This likely failed during the recent record-breaking snowfall event where the nearby Noisy Basin Snotel recorded a whopping 5 inches of water in around 30 hours.

This morning, we dropped the storm slab hazard from likely to possible at upper elevations in the Swan, Glacier Park, and Flathead Range. We reason that storm slabs strengthen within a few days of forming, and it has been several days since our recent heavy-loading event. When the wind returns, thick slabs of wind-drifted snow are expected to develop, and we may need to add Wind Slab to the problem list.

We also dropped the likelihood of triggering a Persistent Slab avalanche to unlikely in the Flathead and Swan zones. We kept it as possible in the Whitefish due to less recent snowfall and subsequently, the weak layer is closer to the surface. Further observations will determine if we can remove this problem. 

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Events and Education:

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