Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Be alert for avalanche hazards that vary with elevation or time of day. Avoid steep start zones with recently-formed slabs of drifted snow. On slopes that haven't avalanched or been overrun by large amounts of debris, it remains possible to trigger avalanches that break on deeply buried weak layers. As the day warms, the hazard of triggered and natural wet snow avalanches will increase on low and mid elevation slopes.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Slabs of drifted snow pose the primary hazard on steep, mid and upper elevation slopes. These slabs formed during the strong winds of the past four days; they may be several feet thick on the lee sides of ridges. Gullies and chutes may also be cross-loaded. A few inches of fresh snow may camoflage older slabs. 

    Hard slabs can be triggered from thin spots at their edges and can break well above a rider, making them poor candidates for slope cuts or traversing. Softer, fresher deposits of wind-blown snow may be the most sensitive to the weight of a rider or snowmachine. If you see linear cracks shooting away from you, step back to sheltered terrain where the snow has not been piled up by wind. The debris from triggered slabs can release much larger, more dangerous slides that break on deeply buried weak layers. 

    (2/24/2025) A large natural avalanche that involved recently-drifted snow. Winds blowing from left to right scoured the left skyline, depositing the snow in and below the large drift below the ridge. Elk Mountain GNP Photo: Jackson George

  • Persistent Slabs

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

    The potential for triggering avalanches that break on deeply buried weak layers lingers on steep mid- and upper elevation slopes that haven't released down to the buried surface hoar and facets that developed in January. It's not clear yet how sensitive these layers are to human triggering after last weekend's storm. Consider them guilty until proven otherwise, particularly southerly slopes where a dense slab sits on facets and crusts. Slides that release on these layers can break surprisingly wide and connect across terrain features.

    Pick routes that minimize your time under steep start zones that haven't avalanched. Digging and testing with large columns is a good way to determine if a persistent slab structure remains intact. Step back to simple terrain if you get propagation or collapses. 

    (2/24/2025)

    The crown of a large natural avalanche that released on weak layers buried at the end of January. The highest extent of the crown is about 6400 feet on a northwesterly slope (U-N-D2.5-O)

    Photo: Drew Mackrell

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    As the day warms, the hazard of triggered and natural wet snow avalanches will increase. Most will be small, though they could have outsized consequences above terrain traps. At low elevations, these slides will involve mostly older snow that has already been saturated. At mid and upper elevations, these slides may involve recently-fallen snow. 

    Rollerballs fanning down a slope are a classic and reliable sign this hazard is building. Use these as prompts to move to shadier or less steep slopes. Avoid sidehilling steep gully walls if you or your snowmachine are sinking more than a few inches into soft, wet snow. The dense, heavy debris involved in these slides is difficult to escape and can result in deep burials on short slopes. 

    (1/30/2025) A reliable clue that the near-surface snow is ripe for triggering: Small wet loose sluffs along creek at ~5600 feet. 

Avalanche Discussion

A widespread but not particularly destructive natural avalanche cycle resulted from the Atmospheric River that swept over the region this weekend. Our observations page has reports and images from across the region (Stryker, Red Meadow, Condon, Stevens Canyon, southern Glacier National Park, Lake McDonald,  the Flathead Range, and west of Choteau). The reported slides include hard slabs, soft slabs, and loose wet snow avalanches. Slides occurred on all aspects. Several trends stand out to me:

  • The deepest, widest crowns appear to be concentrated on shaded, sheltered slopes. I suspect many of these slides broke on the 1/31 buried surface hoar and facets that developed during dry January.
  • Sunny, windward slopes are littered with short, shallow crowns. The slides in this terrain may have released before they overloaded facet/ crust structures deeper in the snowpack. 
  • At upper elevations, slabs appear to have been significantly thickened by wind. 

Until we get more observations, the sensitivity of slopes that haven't avalanched remains uncertain. I'm most leery of slopes facing into the sun at mid elevations, which produced the most consistent signs of instability prior to recent wind, rain, and snow. These may have avalanched before they were overloaded, so the persistent slab structure may remain intact.

With winds mostly diminishing last night, recently formed slabs will have time to stabilize. Today's sun and warm temperatures will start increasing the hazard of wet snow avalanches. I don't expect wet snow slides to be widespread or to gouge deeply, because much of the snowpack already saw a pulse of water from the AR rain. 

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