Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

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

Sustained winds out of the southwest and 4 to 8 inches of new snow will form slabs reactive to they weight of a human. Seek out slopes sheltered from the wind for a relatively safer experience. Persistent weak layers buried 2 to 4 feet deep on north and east aspects continue to show untrustworthy signs. New snow and wind may increase the avalanche danger to CONSIDERABLE overnight.

Lawinenprobleme

  • Wind Slabs

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

    New snow and moderate to strong winds will form fresh slabs of drifted snow on the downwind side of ridges and cross-load gullies further downslope. Expect slabs to grow in size the higher you climb. Slabs will become thicker and more dangerous throughout the day as more snow falls.

    Look for and steer around areas of active wind loading. Identify areas of concern by textured surfaces or dune-shaped drifts. Cracking around your feet or machine is a sign that slabs may be ripe for human triggering. Utilize small, inconsequential terrain features with a partner in a safe location to test how sensitive new slabs of drifted snow are. Sticking to slopes sheltered from the wind will offer a better and safer experience.

    (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
    Possible
    Größe
    1–3

    Buried layers of surface hoar and facets rest 2 to 4 feet below the surface. Avoid common trigger points on the slope by steering around steep break overs or possible thin spots in the slab. If you choose to step out onto steep slopes, select ones with smooth runouts free of surface obstacles. This will reduce the chance of trauma or deep burial.

    All reported avalanches in the last month are on north through east-facing slopes. The most recent avalanche we suspect failed on this layer was on February 10th (3 days ago). Snowpit tests vary between non-propagating and propagating results in extended column tests.  This layer is gaining strength, but we are not out of the woods yet. 

    (2/7/2023)

    Buried surface hoar is found roughly 70 cm to 1 meter below the surface on north through east-facing slopes. 

    Photo: Cam

Avalanche Discussion

New snow accumulations and moderate wind speeds will be the primary factors in changing avalanche conditions today. Forecasts are predicting anywhere from 3 to 8 inches of snow by nightfall, with another 1 to 4 tonight. The Flathead Range and Whitefish Range will see the lower end of those snow totals, while the Swan Range will yet again be favored. Winds are forecast to blow at sustained speeds of 15 to 25 mph at upper ridgelines. If the Swan Range sees the upper end of snow totals or it overproduces, which it tends to, expect the avalanche danger to rise to CONSIDERABLE late today or tonight. We don't expect new snow accumulations to increase the danger rating in the Whitefish Range, Flathead Range, and southern Glacier National Park. 

Assess new snow accumulations throughout the day and adjust your plans accordingly. If you see 6 or more inches of snow accumulate with active wind transport, begin dialing back your slope angle or hunt for wind-protected slopes. Identify and avoid areas where winds are blowing snow into thicker slabs. 

We are more concerned with persistent weak layers on shaded aspects at middle and upper elevations. This is where slabs are thicker, and where collapses (Flathead Range observation) and recent avalanches have occurred in the past week. Weak layers do exist in the northern Whitefish Range, but we are not seeing signs of instability on them yet. This is most likely a result of less snowfall and a lack of a slab above those weak layers. 

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