Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Recent strong winds drifted snow into hard slabs on leeward-facing aspects. A natural hard slab avalanche failing on a facet crust from late December occurred roughly 3 days ago. Seek out slopes protected from the wind for a safer and better riding experience.

Lawinenprobleme

  • Wind Slabs

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

    Look for and avoid areas where winds drifted snow into firm slabs. These will be more common below ridges and saddles. Keep an eye out for signs of cross-loading further downslope. Wind-drifted snow has a textured appearance and slabs typically have a bulbous or dune shape to them. Seek out slopes with soft snow in areas protected from the wind.

    (2/12/2023)

    A natural avalanche that occurred in the past few days. Steer around or avoid slopes where you see signs of recent wind loading. These will be more common on the downwind of ridgelines. 

    Photo: Burket Kniveton

  • Persistent Slabs

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

    A facet crust combination buried 1 to 2 feet below the surface is showing untrustworthy signs. Propagation in snowpit tests and audible collapses occurred in the past week. Natural avalanches also failed and slid on top of a crust formed in late December. A poor snowpack structure exists at elevations above 5000 feet, and is more of a concern in areas where winds thickened a slab above these crusts. Stick to lower angle slopes on north through east aspects, and especially ones where winds formed thicker slabs. 

    (2/13/2023)

    Snow pit profile from the Second Slide avalanche path above the rail. The red line marks the layer of concern. This layer is sandwhiched between two crusts. 

    Photo: Adam Clark

Avalanche Discussion

Yesterday’s (Monday) storm underproduced in all ranges with remote weather stations showing a trace to 2 inches of snow. What didn’t underproduce were the winds. Mt. Aeneas in the Swan Range averaged speeds of 48 mph for 6 hours yesterday morning. The Whitefish and Flathead/Glacier National Park zones didn’t quite hit those speeds, but still clocked averages between 20 and 35 mph.

Winds had little snow to transport since recent sunny weather capped the surface with a sun crust on south aspects, and sustained winds already transported recent snow. The result of this event is likely a hard, stubborn wind slab on leeward aspects and scoured surfaces on windward aspects. If you decide to go out, head to your most wind-protected locations for a relatively safer experience. Expect to find a new melt-freeze or rain crust at low elevations. 

Mark and Sarah visited a crown from a natural avalanche on Mt. Essex in the Flathead Range. This slab failed at roughly 6000 feet on a northerly aspect. It was a hard slab that slid on top of the Christmas Crust. This is evidence that the poor snowpack structure in the Flathead Range reached a tipping point in areas where winds drifted snow into thicker slabs. For the time being, give areas where winds thickened slabs a wide margin for error to allow this poor structure to adjust to recent loading.

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