Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Recently formed wind slabs are gaining strength but triggering a slide large enough to bury or injure you remains possible. Steer around areas harboring stiff, dense snow. In sheltered locations, the surface snow is developing a slab and increasing the threat of a rider affecting a buried weak layer 1-2 feet below the surface. Utilize terrain to your advantage by choosing planar slopes free of convexities. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Slabs formed from windy conditions Friday and Saturday are beginning to gain strength and will not be as reactive today as the previous two days. Winds decreased overnight and will remain light Sunday, limiting new slab formation. If you move into leeward facing terrain, look and feel for evidence of slabs as you gain elevation - a pillowed appearance, stiff, dense snow that you or your machine ride on top of or barely sink into, and possibly hollow-sounding. Cracking beneath you is a clear sign of instability. Utilize hand pits or small test slopes to see how well the slab bonds to the layer below. Default to sheltered terrain for a safer experience.

    (2/5/2022)

    Winds still had some snow to transport at around noon on Saturday. We avoided these slopes at mid and upper elevations. 

    Photo: Cam Johnson

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Reports of a layer of buried surface hoar or facets 1-2 feet below the surface and reactive in snowpit tests continue to trickle in. This week, the buried surface hoar was the failure layer for two skier-triggered slides in the Whitefish Range. Riders in the Flathead Range noted audible failures on these weak layers Saturday. Monday's low-density snowfall is stiffening into a slab, and the likelihood of triggering a slide is slowly rising. We have expanded the distribution of this problem to all aspects in anticipation of this week's warming. Terrain management is the tool of choice for buried weak layers, and we recommend steering around convex slopes in favor of planar slopes with clean runouts.

    (2/4/2022)

    Buried surface hoar is "spotty." It is more common above roughly 6000 feet and on aspects sheltered from the wind. 

    Photo: Mark Dundas

Avalanche Discussion

Wind slab remains our number one problem for another day or two. Wind speeds decreased Saturday evening and look to stay below the threshold for blowing snow today into tomorrow. Slabs that formed Friday and Saturday are slowly gaining strength and allowed us to drop the danger to MODERATE in all zones. It remains possible to trigger a slide large enough to bury or injure you, and all wind-loaded terrain should be evaluated before committing. 

Our Persistent Slab problem may slowly be rearing its ugly head. We have had the pleasure to enjoy the soft snow capping buried surface hoar or facets throughout the week. However, Monday's low-density snowfall is slowly transitioning into a slab. Tuesday's skier-triggered slide in the Whitefish Range was on the leeward side of a saddle. This area developed a slab early in the week due to its location. Friday's skier-triggered slide was on a nearby slope but in a place more sheltered from the wind. It took longer for a surface slab to form in this location, and even here, the slab was not consistent as the third rider found the very soft slab and triggered the slide. This week's warming temperatures will help consolidate the surface snow into more of a slab and increase the likelihood of triggering an avalanche on a buried weak layer.

Cam and Rick, the FAC intern, found a poor snowpack structure which kept them away from steep start zones at mid and upper elevations Saturday in the Middle Fork. They noted weak faceted snow around a crust about a foot down on a southeast aspect. I was in the southern Whitefish Range Friday and found a similar structure on various sunny aspects. An observer in the Swan Range had propagation on faceted layers on a south aspect. A rider in the Flathead Range had an audible failure on a westerly aspect Saturday. These signs point to a broader distribution of the Persistent Slab problem, and we have expanded the distribution to all aspects at mid and upper elevations. 

Regioni coperte