Avalanche forecast

Whitefish Range

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Soft slab avalanches pose a serious threat in the central and northern part of the zone, where a foot or more of new snow fell over the weekend. You can reduce your exposure to this hazard by staying off of and out from under steep slopes if you see recent natural avalanches or hear and feel whumpfing collapses. In the southern part of the zone, this hazard is localized to slopes with about 8 inches or more of new and drifted snow.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    On steep slopes with 8 inches or more of fresh or drifted snow, you can trigger soft slab avalanches large enough to bury or injure a person. These conditions look to be widespread in the central and northern parts of the range, where natural avalanches and collapses were reported Sunday. In the southern part of the range, you'll find these conditions as you climb higher in elevation and into terrain exposed to winds.

    Where the recent snow has buried a layer of surface hoar and facets, it's possible to trigger slabs from below or from adjacent slopes. On slopes that receive direct sun, the weekend's storm snow sits on a slick, hard sun crust. Slabs may be more stubborn on these aspects, though the debris may run fast and far. 

    You can reduce your exposure to the Storm Slab hazard by staying off of and out from under steep slopes if you see recent natural avalanches or hear and feel whumpfing collapses. In the absence of these clues, use inconsequential test slopes and hand pits to check for slabs sensitive to your weight. Avoid committing to steep slopes above terrain traps. 

    (12/8/2024)

    The kind of terrain where you can find trouble today. The fresh snow on this steep, convex slope released as soft slab avalanche naturally overnight on 12/7. 

    Photo: blase reardon

Avalanche Discussion

Accumulations from this weekend's storm were highly variable, leading to marked differences in the avalanche hazards across the region. The storm favored the northern parts of the forecast region, like the 10 Lakes area in the Whitefish Range and the Livingstone Range in Glacier National Park.  SNOTELS in these areas recorded 1.6 to 2.8 inches of SWE and 12 to 14 inches gain in snow height, which likely translates as 12 to 18 inches of storm snow. Meanwhile, the southern Whitefish Range and the Swan Range looked to have picked up only 3 to 4 inches of new snow. The Flathead Range and southern Glacier NP seem to be somewhere in the middle - 4-6 inches at mid elevations, and possibly double that up high. I suspect there are a few black holes in our weather station network that also did well - the Doris and Lost Johnny areas in the Swan, and Lake McDonald in Glacier NP. 

The takeaway is that paying attention to how much new snow is under your boards or machine will give you a good sense of the size and potential consequences of triggered slides. Generally, slopes with about 8 inches or more of new and/or drifted snow have the potential for avalanches large enough to bury or injure a person. 

The storm snow fell on surface hoar, facets, or suncrusts at mid-elevations, and a rain crust below about 5200 feet. It may be a little higher in the southern part of the region. The layers of surface hoar and/ or facets are my primary concern right now. The thin slabs sitting on these were not reactive in my tests Sunday, but further north, where the slabs are thicker and stiffened by wind, riders reported whumpfing collapses and natural avalanches. As the storm snow settles, I suspect slabs sitting on these weak layers will grow more unpredictable. 

Did you hear about the app? 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 win debates about the avalanche problems right in the backcountry or submit an obs while driving home. 

Registration is open for this season's avalanche courses. Get some learning done!  There's an Avalanche Awareness class on Wednesday, December 11th, at 6:00 pm at the Stonefly Lounge in Coram.

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