Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Tue
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

Sustained winds out of the southwest and 3 to 5 inches of new snow will form slabs on the downwind side of ridges and cross-load gullies further downslope. Avoid areas where you see new snow being transported into dune-shaped drifts. Give slabs of wind-drifted snow a wide margin for error where you find them resting over weaker snow. Relatively safer riding conditions exist in areas protected from the wind.

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 leeward facing slopes. 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
    Unlikely
    Größe
    1–2

    A slab is slowly building on top of a facet/crust combination buried 1 to 2 feet below the surface. There is uncertainty about when this weak layer will become reactive. In the past week, observers have noted audible collapses while traveling. Give areas where this layer exists a margin for error, especially where winds drifted snow into a more cohesive slab. If you decide to step out into avalanche terrain, ride one at a time while keeping a partner in a safe location. Choose slopes with a smooth, clean runout free of surface obstacles.

    (2/11/2023)

    In a snowpit at 6900' on an east aspect, the mid-January crust is 1 cm thick and caps a thin layer of facets. The slab has been inverted to expose the underlying facets of this image.

    Photo: Dundas

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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