Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Sun
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 warming and sunshine will increase the chance of a natural or triggered large avalanche on buried weak layers. Wet snow avalanches will increase in size and distribution as the day heats up. Glide cracks and cornices may fail without warning. Give all these problems a wide berth by choosing lower-angle terrain not connected to steep slopes.

Lawinenprobleme

  • Persistent Slabs

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

    Ongoing warm temperatures and solar input increase the chance of a large avalanche on weak layers buried 2-4 feet deep. Many slopes failed during the recent Atmospheric River on sugary facets, surface hoar, or faceted crusts. Today, other slopes may fail naturally or be initiated by a human or a machine.

    Before triggering an avalanche, you may not experience obvious signs of instability like snowpack cracking and collapsing. Persistent Slabs can break much wider than expected and triggered from gentler terrain at the top, bottom, or sides of steep slopes. Surface slides involving wet loose snow or cornice fall could result in a large slab avalanche.

    Wet Slabs may become more likely as the day heats up and water percolates into the snowpack.

    Default to lower-angle terrain not connected to steep slopes to mitigate this problem during the extended thaw.

     

     

    (2/24/2025)

    This image shows the fracture line of a large hard slab avalanche on the east face of Mt Penrose. This weekend's warming could trigger slides like this one. 

    Photo: Mark Dundas

  • Loose Wet

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

    Above-average temperatures and intense late-winter sunshine initiated a natural wet loose avalanche cycle on sunny slopes on Thursday and Friday. Today, natural slides are expected on sunny aspects but may involve snow that is becoming wet for the first time on shady terrain. Regardless, you could likely trigger a loose slide on any steep slope where the surface does not support your weight or the machine's. 

    This morning’s surface crust may break down quickly, especially on solar aspects. Plan your day to stay ahead of the sun, including your afternoon exit. Move to a shadier slope if you note signs of instability, such as sinking into a mushy, wet snow surface. 

    Surface slides could trigger a larger slide on buried weak layers, as described in our Persistent Slab problem.

     

    (2/28/2025) Steep, sun-baked slopes produced multiple wet loose slides on the Swan Front Friday.

    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.

    (2/26/2025)

    Glide cracks like this one could fail during this weekend's extended heat wave.

    Photo: Josh McElrath

Avalanche Discussion

We are amid spring-like weather, with the upper-elevation summit of the WMR ski area reaching 44 F and Hungry Horse 60 F on Friday! Ugh! Expect similar conditions today and on Sunday.

The well-above-average temperatures and prolonged sunshine are coming on the heels of an Atmospheric River and a widespread avalanche cycle last Sunday and Monday. That cycle will likely limit the size and distribution of natural avalanche activity this weekend. However, we expect widespread avalanche activity involving wet snow slides in last weekend's 10-20+ inches of snow. We have uncertainty regarding failures deeper in the snowpack, either from meltwater percolation, such as wet slabs and glide cracks, or buried weak layers tested by the warm-up. 

Recent southwest wind and snowfall from the AR built large cornices, particularly at upper elevations. Warming temperatures will weaken these overhanging features and could cause them to fail. A large block trundling down the slope could initiate a larger avalanche on a buried weak layer. Limit time beneath these features and give them a wide berth when traveling along ridges. 

Yesterday, a frequent Swan Range observer noted that rollerballs and loose wet slides were much more common in the upper elevation band on Friday than on Thursday. Avalanches even occurred around 5:00 p.m. (Image 1, Image 2). The BNSF snow safety team noted larger slides than on Thursday with several D2 wet loose on southerly slopes (Image). A party in the southern Whitefish Range saw a recent slab avalanche likely triggered by the warming temperatures.

The Northwest Avalanche Center (Washington) reported that on Friday, February 28, three snowmobilers were riding near Harts Pass in the East North zone when they triggered a large slab avalanche. Two riders were caught and carried. One rider was fully buried and killed. The other was partially buried and injured. (NE, 6,800ft HS-AM-D2.5-R4-O)

 

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