Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Triggering a large avalanche on a buried weak layer remains possible, especially where the wind has stiffened the surface snow. Thin slabs of wind-drifted snow will continue forming throughout the day, capping older hard slabs. Choose locations sheltered from the wind for softer snow and a relatively safer experience.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–3

    Riders could still trigger a large destructive avalanche on a layer of buried surface hoar or facets 1-3 feet deep. Natural slides failed on this layer during the warm, wet 12/18 storm, with a large remotely triggered avalanche occurring on Thursday. Conditions are most dangerous where wind, dense snow, and warming stiffen the snow surface. The weak layer is best preserved on shady aspects and may be visible as a thin grey stripe in a snowpit wall.

    An unstable slab can be identified by collapsing or whumpfing. Persistent Slabs can unexpectedly be remotely triggered from flat terrain above, below, or to the sides of steep slopes. Areas with softer surface snow will provide a safer experience but not eliminate the risk. To minimize this hazard, choose simple terrain free of convexities with a clean runout below. 

    (12/14/2024)

    The distinct grey stripe in the snowpit wall is the layer of surface hoar and facets buried 12/7.

    Photo: David Steele

  • Wind Slabs

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

    Several inches of snow fell overnight, accompanied by elevated wind speeds. Expect to find thin, fresh slabs in locations favored by snowfall. These should be relatively small but may disguise older, larger slabs formed by intense winds during Wednesday's storm.  

    You will find a mix of hard and soft slabs downwind of ridgelines and on cross-loaded features like gullies. Hard slabs formed on low-density snow and crusts, which may inhibit their strengthening. These slabs can be surprisingly supportive before failing and propagating further than anticipated.  Rippled snow, dunes, and pillow-like features are evidence the wind has been at work. A safer and higher quality experience is found on slopes sheltered by wind. 

    Crown from a large avalanche accidentally triggered by a rider in southern GNP.  This gulley feature was cross-loaded by recent winds. 

Avalanche Discussion

 A quick-hitting storm arrived overnight while temperatures were still warm. Modest precipitation totals of just a few inches of snow and up to 0.5 inches of water at mid-elevation snow stations. We expect snow totals to be slightly higher at upper elevations due to the cooler temperatures. Wind speeds increased overnight, averaging in the 20s with gusts into the 40s and 50s. This unsettled weather keeps the likelihood a rider could trigger a wind slab possible. 

Our persistent slab problem was initially listed in the Whitefish Range on December 10 and then expanded to other zones. Widespread failure on the buried weak layers did not initially occur because the surface was not stiff enough to propagate a failure. Recent dense snow, wind, and warm weather have changed that, leaving a stiff snow surface in many locations. 

Variable snow surfaces are widespread. Choosing locations sheltered from the recent intense winds and above the rain line will offer the highest quality snow while minimizing your risk of triggering a slide on surface snow or a buried weak layer.

Downloaded the app yet? You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can doublecheck danger ratings and travel advice on the drive or in the backcountry. If you’ve experienced any glitches using the app, please email [email protected]

Are you looking for avalanche education opportunities? Check out our calendar for upcoming events. A Partner Rescue Clinic for motorized Riders on January 4 would be a great way to start the new year.  

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