Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist last year abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Continued thawing may increase the avalanche danger. Falling cornice and small surface slides can trigger large and destructive avalanches on buried weak layers. Move off of and out from under steep slopes, especially during the heat of the day. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    Warm temperatures can increase the likelihood of natural and human triggered avalanches on buried weak layers. The resulting avalanches could break surprisingly wide and connect across terrain features. Avoid travel on or under steep slopes that haven't already released on buried weak layers.  Step back to simple terrain, especially if you get propagation or collapses. Meltwater can further weaken these layers, causing avalanches to fail as Wet Slabs.

    Recent winds have formed over-hanging cornice. These may weaken and fail during today’s warming. Although these tumbling masses present their own hazard, keep in mind that they can trigger large and destructive avalanches on buried weak layers. 

     

    (2/24/2025)

    A large slab avalanche on the ridgeline that connects to the summit of Nyack Mountain. 

    Photo: Mark Dundas

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2.5

    Little or no refreeze will make it increasingly difficult to avoid wet snow. Sluffs will be most likely on very steep and rocky slopes that are sheltered from southwest winds.

    Even small slides could have outsized consequences above terrain traps or if they trigger a larger avalanche on a buried weak layer. Rollerballs fanning down a slope are a sign of developing wet snow hazards and a prompt to move to shadier or less steep slopes. 

    (2/27/2025)

    Noisy Creek Drainage. W aspect. A loose slide triggered in the rocks above collected  a lot more snow as it exited the gully.

    Photo: Chris Gotschalk

  • Glide Cracks

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    Warm air temperatures and the intense late February sun have developed conditions favorable for glide cracks to fail. Any avalanches that occur will be large and involve the entire season’s snowpack. February’s snowfall masks many of the cracks visible in January, but they are concentrated on solar aspects at mid-elevations. The likelihood of slides failing increases with our current warming trend.

    This is an unpredictable problem but easy to manage by staying out from under open cracks.

    (2/24/2025)

    A new glide crack has opened on a southeast slope. 

    Photo: Rob Millspaugh

Avalanche Discussion

Yesterday marked the warmest air temperatures of 2025. However, reported avalanche activity was limited in size and distribution (based on only a handful of observations). I suspect a couple factors helped keep the loose wet cycle at bay:

  1. Lower elevations were already worked over by rain during last weekend's Atmospheric River
  2. A crust that formed on solar aspects earlier this week limited entrainment.
  3. Gusty southwest winds cooled windward slopes at upper elevations. 

Temperatures remained above or near freezing at many locations overnight. This will allow mountain temperatures to warm - and any surface crusts to break down- more rapidly today. We may still benefit from the cooling effect of southwest winds, but that's not something I’m counting on as I plan my day. 

Southwest winds may also form thin slabs of wind-drifted snow along exposed ridges and in open alpine bowls. Steer away from obvious signs of wind-affected snow - like etched surfaces or dune-shaped features.  Seek out wind-sheltered terrain if you notice blowing snow. 

Prolonged above-freezing temperatures makes it likely that meltwater is percolating through the snowpack. Liquid water can rapidly destabilize weak layers and glide cracks. Up north, most forecast zones in Alberta and British Columbia have issued a Special Public Avalanche Warning due to warming temperatures and weak layers.

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