Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Watch for recently drifted snow below ridgelines and on the sidewalls of chutes. Use small test slopes to gauge how well slabs are bonding to the underlying surface. On alpine slopes without a hard rain crust, triggering large persistent slab avalanches is still possible. Sheltered, planar slopes less than about 35 degrees are a safer terrain choice as you gain elevation. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Ridgetop winds drifted a few inches of soft snow onto leeward aspects Tuesday. Winds today will decrease gradually and have limited snow available to transport. Recent wind slabs may be stubborn, though they may run long distances down the slope if triggered. Look for recent deposits of wind-blown snow below cornices and in the tops of chutes. Stiff wind slabs may be poorly bonded to low density or faceted snow, crusts, and surface hoar underneath. Test them on small, inconsequential slopes before venturing into bigger terrain. Small avalanches can be dangerous on slopes where terrain traps below magnify the consequences of getting caught. Sheltered terrain will have softer snow, higher quality riding, and safer conditions.

    (1/18/2021) Rounded drifts of snow. Found on the leeward side of ridges above 6,000'

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    The last reported persistent slab avalanches ran on the 13th. Several layers of buried surface hoar remain a concern. One is buried about a foot down, and another 2 to 3 feet below the surface. Stability tests across the region continue to show that they are capable of propagating a fracture across the slope. In areas where you find a stout crust near the surface, you are unlikely to impact the weak layers deeper in the snowpack. Treat upper elevation slopes where the crust is thin, or absent, with suspicion. You can use terrain to limit the chances of triggering one of these notorious weak layers. Stick to planar slopes less than about 35 degrees without terrain traps below if you want to avoid the problem.

    (1/18/2021) Surface hoar buried ~1 foot

Avalanche Discussion

The week started off with a round of small natural avalanches failing on a rain crust as a quick-hitting storm dropped 8" of new snow in the Swan Range. The rest of the region saw only 3 to 5 inches during the same period.

Monday, observers experienced small collapses and cracking in wind drifted snow near ridgelines in the Swan Range and the northern Whitefish Range. They also found 3 to 6 inches of soft snow available for wind transport.

Tuesday, our field team noted increasing winds, blowing snow, and wind slabs forming on isolated middle elevation slopes in the Flathead Range. Wind speeds will be slower today, and upwind slopes will have little snow left to transport. Expect recent drifts to be stubborn, but dense. They developed on top of older, harder drifts, a hard crust, and possibly a patch of surface hoar or near-surface facets. Test how well they are bonding to the underlying surface before committing to steep slopes. If you see more blowing snow or cracking in the snow around you, continue to use caution in big alpine terrain. 

The last reported persistent slab avalanche likely ran on the 13th. However, layers of buried surface hoar and faceted crusts remain a concern. There's one about a foot down and another 2 to 3 feet below the surface. They usually appear as a grey stripe in snow pit walls. Crusts and facets from December are down 4 feet deep. Stability tests show that all these layers can still carry a fracture across the slope. The good news is that the crust that formed on the 13th is generally thick and hard. It covers over these buried weak layers in many locations. The exceptions are where the crust is thinner - on some northerly slopes - and where it peters out at upper elevations. You can spend a lot of time digging and investigating these layers. Or, if you're unsure about the snowpack on the slope where you'd like to play, give yourself a margin for error. Slopes with lower angles, uniform snow cover, and a concave or planar shape are safer than big, complex terrain. 

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