Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Wednesday's new snow and wind-drifted snow will keep dangerous avalanche conditions around for another day. Recently-formed slabs will be larger, thicker, and more dangerous as you gain elevation. Enjoy the soft snow by choosing lower-angle slopes (35 degrees or less) not connected to steeper slopes above.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3

    Strong winds earlier this week formed slabs of drifted snow on steep, upper-elevation slopes. These hard slabs are camouflaged by Wednesday’s snow, which wasn’t accompanied by strong winds. Look for this hazard on the lee sides of ridges and gullies, and downwind of saddles and passes that funnel southerly and westerly winds. Avoid being on or under terrain like this that’s steeper than about 35 degrees. Spontaneous cornice failures can trigger these slabs, so stay well back from slopes overhung by cornices.

  • Persistent Slabs

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

    Weak layers of faceted snow lurk near the base of the snowpack. While our observations in the Whitefish Range Wednesday did not include signs of instability, a forecaster in the Swan Range reported loud collapses and shooting cracks. These are clear signs that the weight of a person or snowmachine can collapse these layers and release large, dangerous avalanches. You’re most likely to trigger a slide on slopes steeper than about 35 degrees where the snowpack is shallow. Convex rollovers – where a slope steepens abruptly – are likely trigger points. The potential for remotely-triggered avalanches continues, so choose uptracks and climbs that keep you out from under steep slopes.

  • Storm Slabs

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

    A soft, dry slab of snow sits over a melt-freeze crust or wet snow below about 7000 or 72000 feet. These slabs are 6 to 18 inches thick. They have failed naturally earlier this week and produced propagation in large column tests as recently as Wednesday. Take shooting cracks and triggered slides on test slopes today as unambiguous signs this combination has not yet stabilized. You're most likely to trigger these slabs on slopes steeper than about 35 degrees, so stick to slopes less than that for stress free enjoyment of the new snow. 

    (12/26/2022) 12/28 1400h 6400' NE. Vehicle-triggered soft slab with dry storm slab visible in top 20cm, moist slab 20 cm underneath.

Avalanche Discussion

This has been an eventful weather week so far. After an atmospheric river led to three days of conditions that warranted avalanche warnings, the temperatures are on a cooling trend, and continued precipitation is abating. 

Wednesday’s surge of precipitation in the Swan Range was striking, as Noisy Basin picked up around 2 inches of SWE in 12 hours! Stahl picked up half of that, with all other stations reporting much less. With a mostly dry day today, we are letting the AVALANCHE WARNING expire and are dropping the hazard at all elevation bands across the forecast area. 

Wet conditions and obscured skies have limited observations of recent avalanche activity. With improving travel conditions, we look forward to observing the natural avalanche cycle that occurred over the past few days. 

I toured with Rob and Blase in the southern Whitefish Range Wednesday, and we found wind-loaded features as our primary concern along ridgelines. With a few stomps, Blase could trigger car-sized chunks of cornices. Cam and his partner were in the northern Swan Range. They felt seven audible collapses at upper elevations with shooting cracks up to 100 feet away. They found this was a stubborn soft slab problem from the recent storm snow, and it was in all aspects.

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