Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
Open full map
Veraltet — dieser Lagebericht ist 2 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

It is possible to trigger a slide on a buried weak layer, particularly on wind-loaded slopes with denser surface snow. A whumpfing collapse indicates you have found an unstable slab. Choose lower-angle terrain or stick to south and southwest-facing slopes where the weak layers do not exist. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Reports of avalanches on buried weak layers have been scant since the 12/7-12/8 storm. In many locations, the overlying slab remains too soft to propagate. Exceptions to this are found in wind-loaded terrain and areas favored by snowfall where the slab is thicker and stiffer. Incremental loading from light snowfall and wind continues today. The weak surface hoar layer is generally found 8-16 inches deep on shaded aspects at upper and mid-elevations above last weekend's rain line. 

    Hand pits or a quick shovel session will identify if the slope you are on harbors this layer. If in doubt, choose a south or southwest aspect. This is where the sun destroyed this layer on many of these slopes. 

    Shooting cracks or a whumpf indicates you have located this problem and should move to a different slope or lower-angle terrain free of overhead hazards. It remains possible to trigger an avalanche from flat terrain above, below, or to the side of a steep slope. 

     

    (12/14/2024)

    The thin grey stripe the gloved finger points to is surface hoar. This layer was found 8-9 inches below the surface on shaded aspects from 5500 feet to the ridgeline. 

    Photo: Erich Peitzsch

Avalanche Discussion

A storm system was expected to impact the Whitefish Range on Saturday and the Swan and the Flathead Range overnight. Unfortunately, this system underproduced with snowfall amounts in the 1-3 inch range, with 0.1-0.3 inches of water. This minor moisture did little to affect the avalanche danger or problems yesterday or overnight. 

Lingering precipitation today will add a bit of weight and stiffness to the slab resting on a layer of surface hoar in the Whitefish Range, Flathead Range, and Glacier Park. Most observations from these two zones report a surface slab that remains too soft to propagate (Observation 1, Observation 2). The exception would be in areas loaded by recent wind that stiffened the snow surface. The 12/7-12/8 warm, wet storm initiated multiple avalanches in the northern Whitefish Range but also rained to ridgeline elevations in the Swan Range and the Apgars. This rain destroyed the surface hoar, and we removed the Persistent Slab problem from those areas. 

We added a Wind Slab problem to the Swan Range on Saturday, expecting this problem to develop late in the day or overnight. That probably did not happen, but we will list this problem today in anticipation of developing light to moderate snowfall. West-to-southwest winds continue an impressive streak of strong average speeds with gale-force gusts at the Aeneas Ridge wind station. 

Did you hear about the app? 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 win debates about the avalanche problems right in the backcountry or submit an obs while driving home. 

Are you looking for avalanche education opportunities? Check out our calendar for upcoming events. Tomorrow, Monday, December 16, there is an Avalanche Awareness Class at Bias Brewing.

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