Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Riding safely will demand conservative terrain choices as you gain elevation. Default to slopes less than about 35 degrees where shifting winds have stiffened the surface into sensitive, textured slabs. Watch for long-running sluffs coming down from very steep chutes and avoid confined gullies above terrain traps - like tree wells, cliffs, and creek beds.

Lawinenprobleme

  • Wind Slabs

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

    Southerly and westerly winds blew low-density surface snow onto leeward slopes Thursday. The newly-formed slabs were reactive in the southern part of Glacier Park. A weak push of Arctic air moved south and west overnight, causing the wind to shift to the north and east. In the Whitefish Range and Glacier, this shift also caused the winds to increase. Use caution on all aspects above about 6,000 feet, below ridges, and on the sidewalls of chutes. Watch for stiffer, rippled snow that may send cracks racing ahead of you. Avoid pillowy drifts on slopes steeper than about 35 degrees to avoid getting caught in a slab avalanche large enough to bury or injure you.

  • Loose Dry

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

    15 to 25 inches of cold soft snow have fallen since the 13th, with little wind. The surface will be incohesive, low-density snow where winds were light Thursday and in sheltered terrain. Sunshine today can tip off natural sluffs of loose snow in chutes and below cliff bands. Avoid overhead exposure to those slopes. You can also trigger them on shady slopes. Avoid confined terrain where you cannot escape moving snow. Avoid very steep slopes above terrain traps where getting carried downhill would have outsized consequences, like above cliff band, creek beds, and deep tree wells. The problem will be more isolated below about 5,000 feet where early season obstacles still anchor the snowpack.

    (12/14/2021)

    Sluffs, like this one, are possible where cohesionless surface snow pours down steep slopes. The sluff in this picture did not entrain much snow and was harmless in size.

    Photo: Reardon

Avalanche Discussion

4 to 16 inches of new snow has fallen in the last 24 hours, accompanied by moderate southwest wind. Observers noted blowing snow on ridgelines above Canyon Creek. Skiers in Southern Glacier Park triggered fresh wind slabs on easterly slopes near and above the treeline (Example 1, Example 2). This continued the trend of sensitive, wind-stiffened slabs. On Wednesday, small avalanches broke from a skier’s feet in the Northern Whitefish Range.

The snowpack, overall, is right-side up. Column tests have mostly failed within the recent snow. Snow depths above about 6,000 feet range from 2 to 6+ feet. The snowpack has a similar structure but is thinner on typically sunny and windward aspects. A thin layer of rounding facets rests atop the hard basal crust buried in early December. We’ve had few reports of stability tests failing on this buried weak layer, except for propagating ECTs in the Apgar Range. Where fresh wind slabs formed on the south- and west-facing slopes, these small weak grains may be closer to the surface.

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