Avalanche forecast

Whitefish Range

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Out of date — this forecast expired 5 years ago.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

One way to wreck your season on opening day would be to trigger a slab of new and drifted snow that carries you into a terrain trap or tree. Avoid this fate by avoiding slopes steeper than about 35 degrees where you find more than about 8 inches of dense snow over soft, low-density snow. These conditions are more widespread at upper elevations, where more snow fell Wednesday and winds were stronger. Shooting cracks are a clear sign you've found this structure.  

Avalanche problems

  • Storm Slabs

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

    On specific slopes, mostly at upper elevations, you can trigger slabs of new and drifted snow large enough to bury or injure you. These can fail at the interface below Wednesday's snow, on a very soft layer of low-density snow or a hard, slick crust. Look for shooting cracks in slabs 8 inches or more thick, on steep slopes (steeper than 35 degrees). At upper elevations - above about 6500 feet - snow cover is deep enough that rocks and other anchors are buried, so the slabs can be wide enough to catch and carry a person. Slopes like that are isolated at  mid elevations, because brush and other anchors are limiting the size of start zones and most slabs are less than about 8 inches thick. 

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!

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