Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
3 · Erheblich
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Kernpunkte

Low-angled, shady slopes hold the safest riding conditions. Sun and warming temperatures will increase the risk of wet snow avalanches on steep sunny slopes without a thick crust on the surface. Dangerous slabs 3 to 6 feet deep may still be sensitive to your weight, or to sudden loading from falling cornices, on steep shaded slopes. Avoid traveling on slopes under glide cracks.

Lawinenprobleme

  • Loose Wet

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

    Sun and rising temperatures will wet the surface snow again today. Freezing levels are forecast to climb to 6,500 feet by late afternoon. This is not the first time this week that sunny aspects have thawed. But, where the top of the snowpack becomes saturated, or where it never re-froze, loose wet avalanches will be possible. The snow near rocky areas or sparse trees will warm first and most. Rollers balls and sinking to your shins in wet snow are warning signs. Use caution on or under very steep slopes getting sun. Stick to shaded terrain or lower slope angles and watch for sluffs running down from above you.

    (2/24/2021) Lower elevation roller balls

  • Persistent Slabs

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

    Sunny weather won’t diminish the lingering threat of triggering large and dangerous slabs, yet. They can break more than 3 feet deep on weak layers buried in January. These persistent layers resulted in triggered avalanches in Skyland and the northern Whitefish Range as recently as last weekend. Slabs will be more sensitive to a rider’s weight on northerly aspects, where winds have stiffened them, where they are less than 3 feet deep, and where there’s no surface crust. It may be harder to trigger the concerning layers where they are deeply buried or where a recent freezing rain crust has locked up the surface. Large cornices that fall may trigger the weak layers regardless. The safest option is to ride slopes less than 30 degrees without mid-slope breakovers or cornices overhead.

    (3/1/2021) Crown and debris of a skier remotely triggered Soft Slab avalanche on 2/28, D2 in size @ 6900' on a SE aspect.

  • Glide Cracks

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

    What looks like brown frowns on solar aspects are glide cracks. The entire snowpack is slumping and slowly sliding down the hill on smooth ground underneath - like bear grass or bedrock. They can fail all at once resulting in very large and dangerous avalanches. That’s more likely to happen when sun and warming temperatures lubricate the bed surface with fresh melt water. Avoid traveling on slopes under the brown frowns.

    (3/1/2021) The brown frown. Glide crack opened up 2/28 or 3/1

Avalanche Discussion

Sunny skies and warm temperatures on Monday produced widespread roller balls below roughly 6,000 feet. Natural sluffs ran from upper elevations to canyon floors on sunny slopes in the Flathead Range. A few large cornices fell naturally in the Apgar Range.

We have reports that a stout freezing rain crust caps the snowpack on all aspects above about 5,500 feet in the central Swan Range, Apgar Range, and the Whitefish Range (observation). It goes to at least 7,000 feet. We know that it’s missing from parts of the Flathead Range and southern Glacier Park. This thick ice crust will likely slow surface melting. If it does thaw, there is up to a foot of dry, low-density snow under the crust that can become wet and unstable.

Between 3 and 6 feet of settled snow from February sits atop the mid-January crust. It’s close to the surface in the southern part of the Flathead Range and Glacier Park. The weak layers associated with that crust produced recent avalanches in the northern Whitefish Range and the  Skyland area. They have also continued to show propagation in snowpack tests in the Flathead Range, southern Whitefish Range, and southern Glacier Park.

Large cornices loom over steep leeward slopes across the region. As the sun warms the roots of these whales, they can crash onto the same slopes that harbor the January weak layers. Whether they trigger slabs on the slopes below or not, they are a hazard in and of themselves. 

Glide cracks are sagging on southerly slopes on the west side of the Swan Range, in the southern parts of the Flathead Range and Glacier Park, and across the Whitefish Range. These cracks are more likely to fail as avalanches that bring down the full depth of the snowpack during periods of intense sun and rapid warming.

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