Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Continued warm temperatures and rain on snow will make it possible for a rider to trigger a loose wet avalanche in the mushy surface snow. Fresh pinwheels and rollerballs signal that the snow surface is moist and ready to slide. Even a small slide can have devastating results if you are swept off your feet and raked through trees, off a cliff, or into a gully. Where the snow surface remains dry, watch for pockets of wind-drifted snow. Approach ridgelines cautiously and move to sheltered terrain if the snow cracks or collapses under your feet or machine. 

Problèmes avalancheux

  • Loose Wet

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

    Temperatures have been above freezing since Thursday evening at mid-elevation weather stations. Melting snow from trees and rocks initiated widespread rollerballs on all aspects below 6500 feet yesterday (Friday). Observations are limited, but we received reports of small wet loose slides in the surface snow on very steep slopes. Natural avalanche activity is waning, but the threat of triggering a slide in the moist near-surface snow remains. Slides may entrain all of the snow that lies above the crust formed around Christmas. Where you find a mushy snow surface choose lower-angle slopes to minimize your risk of initiating a slide. Windward or scoured terrain may hold less loose surface snow and offer better riding opportunities. The snow surface at upper elevations is moist in some locations but should generally provide a better experience.  

    (1/13/2023)

    Recent warm weather triggered this small wet loose slide on a southerly aspect.

    Photo: Mark Dundas

  • Wind Slabs

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

    Southwest winds over the past 24 hours were strong enough to transport snow at many upper-elevations locations. The Aeneas Ridge station averaged 30 mph with a gust of 53. However, warm temperatures and previously wind-scoured surfaces may limit the snow available for transport. In some locations, slabs may be resting on persistent weak layers and could break wider than expected, be remotely triggered, or wrap around terrain features. Cracking around your skis or machine is a sign of wind-drifted snow and a good reason to fall back on safe travel techniques like riding one at a time while your partner watches. You can further reduce your risk by selecting terrain sheltered from the wind.

    (1/13/2023)

    Recent southerly winds built a new lip to this existing cornice. The new portion broke easily under the weight of a skier.

    Photo: Mark Dundas

Avalanche Discussion

Weather stations across the advisory area are currently reading temperatures near or above freezing.  More concerning, is that this trend has persisted for 24 hours or more. Without a refreeze, you can expect to start the day with wet snow surfaces at lower and mid elevations. The potential for rain on snow isn’t going to do us any favors either. Surfaces that were worked over by yesterday’s rollerball cycle will be more reluctant to slide.  Snow that is transitioning to wet for the first time will be more sensitive. This transformation is typically accompanied by a fresh crop of rollerballs. The size of wet loose avalanches will be limited by the amount of snow above the robust Christmas crust.  

Winds remain high enough to drift loose snow at upper elevations. Recent observations, however, have not featured cohesive or sensitive wind slabs. If you do find dry snow today, I would still be skeptical of potentially wind-loaded terrain along ridges, chutes, and gullies.  Don’t forget that it was only three days ago (Wednesday) that riders remotely triggered an avalanche on wind-loaded terrain in the Swan Range.  This slide likely involved a buried weak layer, like facets or preserved surface hoar.  

Temperatures and wind are both forecasted to decrease throughout the weekend.  If this forecast verifies, expect the trend to shift towards generally stable avalanche conditions Sunday.

Did you wake up to the sound of rain this morning? Are you making plans to hunt dry snow above the freezing level?  If so, hop on the rain or snow app and let the good folks at the Desert Research Institute know what’s happening. Your data will help improve forecasting for mixed precipitation events.  This is a constant challenge in Northwest Montana, so be a pal and give us a hand.

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