Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Beat your way through the bush and downed trees to reach higher terrain, and you may be greeted by slabs of drifted snow that, if triggered, can rapidly and roughly send you back downhill. Avoid this fate by sticking to slopes less than about 35 degrees or those where the surface snow isn't wind-packed and dense. 

Avalanche problems

  • Wind Slabs

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

    Slabs of wind-blown snow 1 to 2 feet thick pose a danger on steep slopes at upper elevations. Look for these top-loaded onto the lee sides of exposed ridges, near summits, at the tops of chutes, and downwind of saddles and passes. They may lurk on the lee sides of gullies and other exposed, mid-slope terrain features at upper elevation. Ye shall know them by their feel - dense or hard snow that doesn't allow you or your machine to sink much below the surface. You can keep things simple by sticking to slopes where the snow surface remains unconsolidated, or slopes less than about 35 degrees. 

    (12/8/2021)

    Dense, textured snow that cracks under you in leeward terrain is a sign that you could trigger a wind slab avalanche.

    Photo: Reardon

Avalanche Discussion

As you climb higher today, avalanche hazards will be more widespread and more consequential. But that's about as broad brush as I can get, because the size and distribution depend on very local influences that are combining differently within the different zones, and across the region. 

  • Wind-drifted snow: Wednesday saw moderate to strong westerly winds across the region. These winds were strong enough to transport snow and drift it into slabs. Wind speeds were more  consistent at upper elevations, so expect more and thicker slabs of drifted snow as you climb towards exposed ridges and peaks. The Whitefish Range has less terrain like this, so expect the problem to be localized to the higher peaks in the center of the range. Winds died down after dark and aren't forecast to pick up today, so the slabs shouldn't grow much.
  • A rain crust deposited 12/7. Clancy reported this crust was widespread in Noisy and Jewel Basins in the Swan Range Wednesday; I didn't find it at all in the southern Whitefish Range but WMR patrol reported it from a few spots on northerly slopes. For now, expect this crust in the southern half of the region (let us know if you find it elsewhere). Where this crust existed prior to Wednesday's snow and wind, it limited the amount of snow available for transport. So more rain crust, less wind-drifted snow. But a better sliding surface for new snow, so look out for small, loose dry sluffs on steep slopes where new snow accumulates.
  • A dense soft slab over a very soft, low-density layer. This structure was widespread and reactive Wednesday in the southern Whitefish Range, producing shooting cracks on steep slopes on all aspects. It was harmless, however, because the slab was only 4 to 5 inches thick and shallow snow cover and thick brush limit the size of start zones. However, it could be dangerous where it's thicker than about 8 inches and in larger start zones with contiguous snow cover. It should give itself away with shooting cracks. I expect this problem to heal quickly. It's not clear if it's distributed more widely than the southern Whitefish Range. Again, let us know if you find it elsewhere.

Look for these three factors as you travel today and adjust your plans and terrain choices to match what you find. Slabs of drifted snow 1 to 2 feet thick will be the most consequential hazard, with generally less consequential hazards from the Storm Slab or Loose Dry avalanche problems.

November's record warm weather has one upside - less concern about basal weak layers in the snowpack, thanks to hard, thick layers of refrozen melt-freeze grains below the snow since 12/3. So far, we have little evidence that a person's weight can trigger slides near the ground. We'll continue to monitor those layers.

And thanks to the deep technical expertise of Nohow Inc, the WMR Summit weather station is again sharing its data with the internet. Just in time for opening day!

Regions covered