Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

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

Points saillants

You'll find the best riding in lower-angled terrain sheltered from the wind today. Avoid steep, shaded slopes above terrain traps, where it remains possible to trigger dangerous avalanches that break 1 to 2 feet deep on older, buried weak layers. Freshly formed slabs of drifted snow pose a hazard at upper elevations. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–3

    Remain wary of steep, shaded slopes with convex profiles. In this terrain, you can still trigger avalanches that break 1 to 2 feet deep on weak snow buried in early December. These slides can connect across multiple start zones, and can be triggered from below or from adjacent slopes. Sidehill, climb, or descend lines that aren't above gullies, trees, and rocks. 

    Recent observations indicate the 12/7 persistent weak layer is better developed in some parts of the forecast region, such as the northern and central Whitefish Range and the east side of the Swan Range. Assume this variability exists within the area you're traveling. Nasty surprises are possible even when you don't feel any collapses or see any shooting cracks.

    If you dig below the snow surface, the weak layer often appears as a distinct grey line. Areas where you find this structure remain the most problematic. Propagation and/ or collapses in column tests are evidence that the layer remains sensitive to your weight or the weight of a snowmachine. 

    (12/21/2024)

    A party in the Central Whitefish Range checked before committing to steep terrain Sunday. Their large-column test propagated with 11 hits, and they stuck to lower-angled terrain with fewer consequences. A good model for how to approach steep slopes today.

  • Wind Slabs

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

    Steep, upper elevations slopes that collect wind-blown snow may harbor fresh slabs that can be dangerous above terrain traps.  These may grow thicker and more widespread with today's new snow and continued southwest to west winds. They may also camoflage older, harder slabs formed by Wednesday's intense winds. 

    Be alert for steep slopes with drifts deeper than about 8 inches. These slopes will become more widespread as you climb higher in elevation. Unstable slabs often give themselves away with shooting cracks. Cornices can be a giveaway that the slope below has been collecting wind blown snow and slabs sensitive to your weight are possible. 

    (12/20/2024)

    A small wind slab is visible just beneath a cornice near the summit of Elk Mountain. This slide likely failed during the intense wind event of 12/17-18. 

    Photo: Mark Dundas

Avalanche Discussion

Over the past week, a series of weak, warm storms has paraded across the region. It hasn't been a parade of big, dramatic floats. More like folks in toy cars spinning down the street. The exception was the event on Wednesday, 12/18. Winds have consistently blown from the west through the southwest.

The results are slowly thickening - and consolidating - slabs above the 12/7 persistent weak layer. It consists of buried surface hoar and small facets and remains our primary avalanche concern. The weather pattern is accelerating the variability present when it was initially buried. So the slabs above it are becoming unreative on some slopes - like I found Saturday east of Whitefish Mountain Resort. Others, however, still pose a serious hazard. Unfortunately, these are often the same slopes where the snow remains soft and dry, and thus most attractive.

You can protect yourself against this variability by being disciplined in your terrain choices and route-finding. Yeah, I know; "disciplined" doesn't sound like fun, especially on a holiday week. A party in Kimmerly Basin on Sunday might disagree. They saw the crowns from recent avalanches near ridgelines and stuck to lower-angled, lower-elevation trees in the basin. "An absolute blast..soft snow with good body for traction." They didn't let their excitement or the increasingly tracked snow lure them back to the steeper terrain with recent avalanches. Similarly, a party in the central Whitefish Range stuck to lower-angled, less consequential terrain after a large column test propagated with moderate force. 

Today's new snow and gusty winds might combine to create or continue building small, mostly soft slabs in wind-exposed terrain. The debris from triggered slabs of wind-blown snow might release slabs that step down and break deeper on the 12/7 weak layer. Another reason to be choosy about your lines in upper-elevation terrain today.

Downloaded the app yet? You can now access our region's forecasts, observations, and weather data directly from the Avy App (IOS; Android). Many features are accessible offline, so you can doublecheck danger ratings and travel advice on the drive or in the backcountry. If you’ve experienced any glitches using the app, please email [email protected]

Want to start your New Year on the right foot? Sign up for a Partner Rescue Clinic for motorized Riders on January 4 . Check out our calendar for other upcoming events. 

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