Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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

Recently formed hard slabs may be masked by yesterday's snow. You're most likely to trigger a slide in terrain that the wind has loaded. You can reduce your risk of triggering slides today by avoiding steep, rocky, wind-affected slopes.

Avalanche problems

  • Wind Slabs

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

    Wednesday and Thursday's gale-force southwest winds drifted substantial snow into thick, hard slabs. A wind shift to a north and east direction Friday and Saturday may have built thin slabs in locations favored by atypical winds. A return to southwesterly flow is transporting Saturday's low-density snowfall. 

    Recently formed hard slabs may be masked by yesterday's snow. They may sound hollow like a drum, support you and your machine, and offer no signs of instability until they fail. Features formed over the past 48 hours should provide more straightforward clues, such as drifts, dunes, rippled snow surfaces, and snow pillows. Cracks shooting away from you indicate you have found an unstable slab directing you to sheltered or lower-angle terrain. 

    On Saturday, riders in the Whitefish Range found thin reactive slabs in sheltered locations. This instability probably formed due to intense precipitation intensity and should be short-lived. However, look for slopes holding cohesive snow in the trees. 

    Saturday's low-density snow may sluff on steep slopes in sheltered locations, primarily where this snow rests on a slick recently formed rain crust or a thick layer of cohesionless powder. 

     

    (2/29/2024)

    Active wind-loading of a cornice on a ridgeline at 6700 feet. 

    Photo: Mark Dundas

  • Persistent Slabs

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

    During Wednesday and Thursday's snowfall and intense wind events, a layer of weak, faceted snow buried 2-4 feet was the failure layer in multiple large avalanches. This layer is several inches above the hard, early February ice and crust on shady, mid- and upper-elevation slopes. This weak snow has been challenging to identify in snowpits and does not always produce concerning results in stability tests. 

    This week's cool temperatures will slow the strengthening of this weak layer. You may not experience any signs of instability like collapsing or cracking before triggering a slide. 

    Choose terrain free of convexities to increase your safety margin. Steer around thin areas, such as those scoured or peppered with rocks, in favor of a deeper, more consistent snowpack. Cracking beneath your boards or machine indicates an unstable slab directing you to lower-angle terrain. 

    (3/2/2024)

    The crown of a very large avalanche with a width of over 1000 feet on Nyack Mountain. 

    Photo: Mark Dundas

Avalanche Discussion

Most locations experienced a brief, intense shot of precipitation Saturday. Widespread snow totals are generally 3-6 inches, with the northern Whitefish Range and the Flathead Range favored and the Swan Range a distant third.  Fortunately, temperatures have cooled since last week's valley floor 50F readings, with the snow line now below 1000 feet. Cold arctic air is spilling over the Continental Divide on the far eastern edge of our advisory area with -3F at Marias Pass this morning. 

Saturday, experienced backcountry groups found enjoyable riding in sheltered locations. A party in the northern Whitefish Range experienced up to 16 inches of dry, unconsolidated snow with no instabilities observed. A group in the southern Whitefish Range found the new storm snow touchy and noted multiple (10+) thin D1-size slabs in sheltered locations. They wisely maintained wide margins, only exposed themselves to nonconsequential terrain, and intentionally stuck to low-angle and low-consequence slopes throughout the tour. A group in the Flathead Range noted calm conditions in a drainage sheltered from the east winds. They had 3 inches of afternoon snowfall with some sluffing in the new snow, and 5300 feet seems to be the transition point from good skiing to more spicy.

FAC staff traveled to Cascadilla Creek to look closer at a very large avalanche on Nyack Mountain. Unfortunately, our visibility window was limited to a short period when we were still well down the valley from the slide. However, we did get enough of a view in the flat light to recognize this slide is very large, with a crown exceeding 1000 feet wide. This slide failed during the intense wind-loading event on Wednesday night or Thursday morning. It likely failed on a layer of weak faceted snow above the early February crust. We did note that rain had affected the low and middle elevations of this drainage, leaving behind a widespread surface crust (photo) and well-developed runnels (photo), which made skiing challenging. 

 

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