Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

On upper-elevation, shaded slopes, you can trigger slabs that break one to two feet deep without obvious signs of instability. Decrease your risk by choosing terrain with a consistent slope angle and free from hazards like cliffs, gullies, and exposed rocks and trees. Travel one at a time and watch your partner from a safe location.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2.5

    Triggering a slab that breaks on a weak layer one to two feet deep remains a hazard. The weak layer consists of faceted snow and sometimes surface hoar a few inches above a very hard crust or ice layer formed in early February. This layer is not distinct on some slopes, though the crust and ice are apparent. The hazard exists primarily at upper elevations on steep, shaded slopes, and resulted in two recent accidents and two near misses. You can find this hazard on isolated slopes elsewhere, including middle elevations and solar aspects.

    Reduce your risk through careful terrain selection during your climb, traverse, or descent. Evaluate slope angles, slope shapes, potential trigger points, and the consequences of a slide.  Good options include slopes that are less than 35 degrees in steepness, concave (bowl-shaped) or planar in shape, and not peppered with rocks and trees or punctuated by cliff bands, gullies, or abrupt benches. 

    (2/17/2024)

    A look at the site of the 2-17-24 avalanche accident at the head of Marion Lake, taken before the accident. The shaded slope to the left is where the accident occurred. It faces northeast, as is evident from the shadow, and has a convex entry. The small trees below are a terrain trap.

Avalanche Discussion

Once bitten, twice shy: that’s my attitude toward the current persistent slab problem. With two accidents and two near misses in the last week, I feel a bit shier than I usually might at Moderate danger. 

Besides these incidents, the weak structure has not given obvious signs of instability, like cracking or collapsing. Furthermore, this structure has been challenging to identify in pit profiles and tests, although more recent observations are finding propagation in ECTs. The weak layer presents as a layer of rounding facets and patchy surface hoar 1-2 feet below the surface and a few inches above the stout and well-documented crust from early February. In some cases, it is barely softer than the overlying slab. It has fooled experienced parties, including FAC forecasters.

During my brief tour outside of WMR yesterday (Thursday), I had the luxury of finding an obvious layer of buried surface hoar roughly one foot deep, which propagated with moderate force. This prominent layer appears to be the exception and not the norm. Elsewhere, I'm placing less emphasis on my interpretation of the snowpack and more on spatial variability and uncertainty. The recent incidents and close calls are good reasons to reevaluate and consider increasing your margins by dialing back to less aggressive terrain. 

With minimal new snow, we've elected to drop the wind slab problem. Winds at Aeneas Ridge in the Swan Range, Hornet in the Whitefish Range, and along the continental divide have remained adequate for transport and may increase throughout the day. If you are in one of these areas and notice the hallmarks of wind-effected snow, like a scalloped surface or dune-shaped features, consider moving to less steep or more sheltered terrain. Warm temperatures and sunshine in today's forecast mean there is potential for some small wet loose activity; however, this again will be limited by scant snow on crusty solar aspects. Pay attention to the weather and the snow surface throughout the day. If you're on a southerly slope with more than 8 inches of loose snow transitioning to wet, it's probably time to find less steep or less sunny terrain.

Friends Fest is Here! February 21st-24th: Check out Workshop Night (Tonight) with State of the Snowpack and USGS, Hot Dog Days, Ultimate Après with Backcountry Partner Speed Dating, and the Big A$$ Raffle. More info at flatheadavalanche.org/event/friendsfest

 

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