Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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

This will be an excellent week to get above the valley inversions to enjoy the views and a strengthening snowpack. The chance of triggering a slide on a deeply buried weak layer is decreasing but remains possible at upper elevations. Look and feel for isolated slabs of wind-drifted snow in locations favored by wind.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    There is a decreasing chance a rider could trigger an avalanche on a buried weak layer formed in November. The combination of a deep snowpack and a recently formed crust limits our ability to affect weak layers near the bottom of the pack. Identifying and steering clear of areas harboring a thin snowpack is a good practice. These include scoured slopes on the windward sides of ridgelines and starting zones peppered with rocks. Convexities are locations where the snowpack is at odds with itself and should be given a wide berth. Below the convexity, the snowpack wants to move downhill, while above, the pack wants to remain in place. When in doubt, default to lower-angle terrain for a less stressful experience. We have removed the middle elevation band (5000 - 6500') from the Persistent Slab problem. Please see the discussion for an explanation of why. 

  • Wind Slabs

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

    Wind speeds at most mid and upper elevations have been remarkably calm for the past couple of days. However, a few stations reached speeds capable of transporting snow on the 30th and 31st. Observers over the weekend noted a few locations of recently drifted snow. In areas favored by the wind, such as the downwind side of higher peaks, you may find isolated slabs that are small and thin. These should be generally harmless unless they knock you off your feet and push you into a surface obstacle. Look for cracking beneath your feet or machine and feel for denser surface snow. Areas holding loose surface snow will offer a higher quality experience.

    (1/1/2023) Cornice development.

Avalanche Discussion

This morning we removed the middle elevation band from Persistent Slab on our avalanche problem list. Persistent Slab at mid and upper elevations has been listed daily since forecast operations commenced on December 3. There are several reasons for this removal.

-The substantial rains from the December 25-28 Atmospheric River soaked the surface snow with 2-3 inches of water. After several days of cool weather, this surface has become a thick, strong crust at many locations below 6500 feet. The crust varies in thickness and strength but is generally several inches thick and supportable to someone on skis. Because it supports our weight, it limits our ability to affect the weak layers buried in mid-November.

-Due to the continued development of our snowpack, the weak layers are deeply buried and up to 3 meters below the snow surface. Generally speaking, our ability to affect layers through our weight is confined to the top meter of snow.

-The weight of the overlying snowpack is compressing the weak layers. This is a strengthening process where pore space is reduced, and the crystal shape may change from angular to round.

-A deepening snowpack generally reduces the temperature gradient in the pack. A smaller gradient is a strengthening process that changes the crystal shape toward a more rounded appearance. Round crystals can pack together tighter and thus become a stronger layer.

The number of slopes below 6500 feet where you could trigger an avalanche of a buried mid-November weak layer has been significantly reduced. However, areas of concern remain in places without a supportable crust or where the snowpack is shallow, wind-scoured, or peppered with rocks. Try to identify these locations in your travels and continue to give them a wide berth.

Training: Make 2023 the year of companion rescue skills. Transceiver parks are open at Whitefish Mountain Resort, one at the summit and one adjacent to Grey Wolf. Both are accessible to snowmachines. You can get more details about training and education opportunities events on our events calendar.

 

 

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