Lawinenlagebericht

Swan Range

Flathead Avalanche Center
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Lawinengefahr

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

Light snowfall and breezy conditions keep the danger elevated at upper elevations. You could trigger an avalanche where the winds have formed drifts or stiffened the snow surface. Sheltered terrain should provide an enjoyable safer experience.

Lawinenprobleme

  • Wind Slabs

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

    Yesterday's storm deposited up to 10 inches of snow in the Flathead Range, with 3-4 inches in the Swan and Whitefish. During the day, moderate to strong southwesterly winds transported snow onto leeward aspects at mid and upper elevations. Sustained wind speeds diminished overnight, but gusts remain strong enough to continue moving snow throughout today. Locations favored by recent snowfall will have the thickest and most extensive slabs. Look for these features near ridgelines and mid-slope terrain features like ribs and gullies. 

    Slabs may form on weak faceted snow or crusts, inhibiting bonding and potentially propagating wider than expected. Blowing snow will indicate which slopes are most dangerous. You've likely found a wind slab if the soft, light snow you're moving through suddenly becomes heavy (dense) or you run up onto stiff snow that supports your weight. Cracks shooting out from your skis or sled indicate the slab's instability. Choose terrain sheltered from the winds for a safer, more enjoyable experience.

     

    (4/1/2023)

    Gusting and swirling winds were transporting snow but no slab formation.

    Photo: Kevin Oberholser

Avalanche Discussion

Yesterday's storm favored the Flathead Range and southern Glacier Park. This morning there is a settled depth of 5" on the valley floor in John F. Stevens Canyon at Shed 4 (4557'),  7 inches at Marias Pass (5230'), 9 inches at Shed 11 (6400'), and 10" at Tunnel Ridge (5895'). Hooray! Unfortunately, Noisy Basin in the Swan Range only picked up 4 inches, with a disappointing 2-3 inches in the Whitefish Range.

Westerly winds ramped up during the day Saturday with sustained speeds of moderate and extreme (gale force) gusts. A moderate classification (17-25 mph) is vital because snow generally begins to drift at speeds above 15 mph. Extreme winds are over 38 mph and lead to snow being transported further downslope than commonly seen or the snow sublimates into the atmosphere. Gusts topped 50 mph at many stations yesterday, with Tunnel Ridge taking home the gold with a 72 mph reading. The Aeneas Ridge wind sensor appears rimed and has not conveyed accurate wind data since 1800 yesterday.  

Due to yesterday's snowfall below forecasted in the Swan and Whitefish Range, we are dropping to LOW danger in the middle elevation band. We are also removing the Loose Dry problem from these zones. Loose Dry slides are still possible in these areas, but the size and likelihood are not significant enough to list.

Yesterday, an experienced rider in the Flathead Range noted 4 inches of new snow, and gusting and swirling winds, but there was no slab formation in the area he traveled up to 6500 feet. This individual triggered a sluff on their north-facing descent that traveled 1200 feet, listed in the Flathead Range Loose Dry problem. FAC's friend in the Swan Range noted an intense graupel shower which left 1 inch at 3000 feet. They also noted moderate to strong winds, which diminished in the evening. Upper elevations were obscured, so there were no estimates for transport. 

There remains a slim chance that you could trigger a slide on a buried weak layer resulting in a large avalanche. Thin, wind-swept, or rocky areas are locations where the layer is closest to the surface and where your weight is most likely to affect this weak snow.

FAC will issue daily forecasts through Easter Sunday, April 9. Following this, we will give snowpack updates several times a week through April if conditions dictate. 

 

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