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

Southwest winds and new snow continue to build slabs that are reactive to a rider’s weight. These fresh slabs are likely to be small, but have the capacity to knock you off your feet and push you into places you don’t want to go. As you travel, pay attention to blowing snow and changes in the snow’s density.

 

Lawinenprobleme

  • Wind Slabs

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

    Today’s elevated southwest winds and new snow are building slabs of wind-drifted snow near ridgelines and cross-loaded terrain features like gullies and ribs. These slabs are likely to be small but may be able to knock you off your feet and send you downslope. As you gain elevation, you can expect to find thicker and larger slabs.

    Pay attention to the blowing snow and the density of the snow you travel through. Look for clues that the wind has been at work, such as drifts, dunes, rippled snow surfaces, and snow pillows. Cracks shooting away from your machine or boards indicate you have found an unstable slab directing you to sheltered or lower-angle terrain.

    (3/9/2024)

    Intense wind transport near the Great Northern Mountain. This process builds cornices and develops wind slabs on leeward aspects. 

    Photo: Ernesta McIntosh

  • Persistent Slabs

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

    In isolated locations, a layer of weak snow exists 2-4 feet below the surface. This weak layer is best preserved and most problematic on shady slopes; however, in some locations, sunny aspects contain a mix of crusts and faceted layers capable of producing a destructive slide.

    You're most likely to trigger one of these beasts in steep, rocky terrain similar to the photo to the right/below. Signs of instability, such as cracking or collapsing, may not be present before the slope you are on slides. Choosing lower-angle terrain without convexities is the easiest way to manage this problem.

    (3/9/2024)

    This is a crown of a hard slab avalanche on Mt Penrose. This likely failed on a layer of facets above the early February crust during the intense wind loading event of late February.

Avalanche Discussion

Overnight, a warm and windy storm brought snow to favored locations. Precipitation at SNOTEL sites varied from 0.5 inches at Noisy Basin and Stryker Ridge to 0.7 inches at Stahl Peak and 0.8” at Flattop in central Glacier Park. Tunnel Ridge leads in new snow depth with 8 inches of settled snow. Light snow continues today; however, the primary driving force of the avalanche hazard will be the moderate to strong southwest winds.

Fresh wind slabs will continue building throughout the day as elevated southwest winds buffet our area. Recorded wind gusts in the past 24 hours include 60 mph at Hornet, 94 mph at Tunnel, and 53 mph at Aeneas Ridge.

Among the few observations we received on Sunday, skiers and riders mainly mentioned the distinct snow/rain line at 4000 feet. Low elevations in our forecast area saw decreases in the snowpack as the warm storm continued overnight.

The Flathead Range continues to have a majority of large-to-very-large avalanche activity. Saturday’s good visibility brought more observations of these impressive crowns (photo, photo). However, since March 4th, we have had reports of 4 human-triggered slides in the Whitefish Range. Additionally, we have received word of an observation of large hard slab activity in Hay Creek in the Whitefish Range. If you're out and about and notice any large crowns, let us know so we can continue documenting the distribution of this problem. 

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