Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Sun
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

The snowpack is generally stable. There remains a chance you could trigger a 2-3 foot thick slide on a buried weak layer at upper elevations. The thin snow coverage increases your risk of injury from surface obstacles.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    Triggering an avalanche on a buried weak layer 2-3 feet below the surface is a low-probability, high-consequence scenario. The early December rain destroyed the weak layers or capped them with a crust in many locations. Buried weak layers appear best preserved on wind-sheltered slopes that are shaded and face NW-NE-E. Cam and Rob were in the Flathead Range on Wednesday and found the 12/1 surface hoar layer intact and reactive in terrain that fits this description. The only way to recognize that the slope you are on is suspect is to dig down and verify what’s underneath your feet or machine. Clear signs of instability, such as collapsing or whumphing, may not be present. Choose slopes where you find a robust crust or default to lower-angle terrain. 

Avalanche Discussion

The workweek weather was characterized by dry conditions, generally light winds, and inversions with a thick layer of stratus clouds in the mid-elevation band. Wednesday, sunny skies above the cloud deck warmed the surface, resulting in a thin crust thickening with elevation. Yesterday (Friday), the WMR ski patrol reported small, wet loose slides on steep mid-elevation sunny aspects. This benign weather pattern will continue through Monday.

During periods of stagnant air, there is generally a lack of wind. That was the case this week except for a slight uptick on Wednesday at the Aeneas Ridge (7186') wind station in the Swan Range. Moderate southwest winds throughout the day and overnight drifted snow into thin slabs, resulting in a small skier-triggered slide in Noisy Basin. In many locations, a surface crust caps last weekend's 10-20 inches of dry snow, minimizing or eliminating possible wind transport. However, as always, look for small, lingering slabs of wind-drifted snow on leeward aspects as you gain elevation.  

We continue to list persistent slab as our only avalanche problem and have trimmed the distribution of this layer to upper elevation NW-NE-E aspects. The early December Atmospheric River rain event reached many locations, destroying buried weak layers or capping them with a rain crust. However, the Flathead Range and Glacier National Park remain in Moderate danger due to the tendency for this terrain to produce more significant and more consequential avalanches.

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