Bulletin d’avalanche

Swan Range

Flathead Avalanche Center
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Danger d’avalanche

Mon
Alpin
1 · Faible
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Shifting winds may expand the areas where you could get into trouble. You could trigger a slide on slopes where the wind has stiffened the surface or formed drifts. Thin, loose slides may occur on steep terrain in areas sheltered from the wind.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1–2

    Yesterday, observers noted up to nine inches of recent snow at mid-elevations in the Swan Range. Westerly winds were strong enough at the Aeneas Ridge weather station to transport this snow onto the easterly side of the compass. The wind shifted to the north and east overnight, moving snow toward the westerly side of the compass. Today, you may encounter thin fresh slabs on any aspect. We expect these to be confined to upper elevations generally, but you may encounter them in isolated mid-elevation terrain. Wind features may form along and beneath ridgelines and further down the slope near ribs and gulleys. Slabs may form on sun crusts, wind board, or faceted weak surface snow, adding to their instability.

    Blowing snow, textured surfaces, and smooth pillows should help identify these features. Cracking in the snow beneath you or your machine indicates an instability directing you to terrain sheltered from the wind. 

    ADDITIONAL DISCUSSION: Saturday, riders noted sluffing in the new snow on steep slopes sheltered from the wind. This is primarily a concern where cohesionless snow rests on a slick crust. Expect to manage your sluff if you plan on riding sustained steep terrain. Limit the consequences of getting knocked off your feet by choosing runouts free of trees, rocks, or confined gulleys. 

    (2/16/2023)

    Moderate to Strong southwest winds transported snow on Nyack Mountain.

    Photo: MD

Avalanche Discussion

Despite relatively uninspiring weather, we received six public observations from around the area Saturday. The overall theme was stable conditions on the surface and in snowpit tests. Riders reported surprisingly good and fun times, especially on northerly aspects where Friday's snow rested on softer snow. In the Swan Range, observers enjoyed 4-9 inches of fresh snow, with 3-5 inches in select areas of the Flathead. The new snow was not bonding well to the underlying layer, with sluffing the number one avalanche problem on steep slopes. Light winds had formed small thin slabs in select locations with cracking experienced beneath skis, but no triggered slides.

This morning we dropped the Persistent Slab problem from the Whitefish Range, the Flathead Range, and southern Glacier Park. There are several buried weak layers in our snowpack that have proved troublesome this season but are strengthening and becoming difficult to trigger. With relatively deep snow depths across the area, these layers are generally buried at a depth that a rider is unlikely to affect. However, as recent avalanches signify, thin areas in the snowpack are likely trigger points. These include rocky outcroppings and wind-swept or scoured locations where the weak layer is closer to the surface.

Recently, observers have submitted photos of a few of the many glide cracks opening up around the area (Observation 1, Observation 2). These seem most prevalent at mid-elevations on sunny southerly and westerly slopes. One experienced rider in the Swan Range noted glide cracks on basically every open/ planar slope facing south and west from Strawberry to Peters Ridge. The recent below-average temperatures kept these in place, and this week's forecasted cool conditions should limit glide failure. However, glide avalanches are notoriously challenging to predict and can occur at any point in winter or spring. A good example is a glide avalanche first spotted on Christmas morning in 2020 that failed the following day. Information on that large slide in the Flathead Range is found in this observation.

FOFAC Event: March 30th, 2023– Whether chasing tan lines, big lines, or both, you'll learn something valuable from FAC Lead Forecaster Mark Dundas about spring avalanche problems, how they differ from winter problems, and how to manage them. We will also discuss current conditions and concerns (or lack thereof!) with our spring snowpack. Enjoy a cold brew from Bias Brewing and a scoop from Sweet Peaks Ice Cream. The event is free and open to everyone. Begins at 6 pm.

 

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