Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The avalanche danger is rising at upper elevations, where you are likely to trigger slabs of drifted snow 1 to 2 feet thick. Avoid this hazard - and find better riding conditions - in terrain sheltered from the wind, where the near-surface snow remains loose. Stay out of avalanche runouts at mid elevations if you see blowing snow near ridgelines. With more snow and strong winds forecast for the next few days, expect dangerous conditions to become more widespread. 

Avalanche problems

  • Wind Slabs

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

    The hazard posed by slabs of wind-drifted snow will increase as you climb higher in elevation today, and as the day progresses. At upper elevations, you'll find slabs 1 to 2 feet thick on the lee sides of ridges, downwind of saddles and passes, at the tops of couloirs, and crossloaded into gullies. These slabs will continue building through the day. Shooting cracks and whumpfing collapses are clear signs that these slabs can be triggered by the weight of your gung-ho buddy or brand-new snowmachine. At mid-elevations, expect isolated slabs of wind-blown snow large enough to bury or injure a person, mostly on steep slopes prone to collecting drifting snow.

    (12/21/2021)

    Recent winds have left a slab on the snow surface in the Apgar Range.

    Photo: Mark Dundas

Avalanche Discussion

Tuesday's observations highlighted the effects of moderate to strong winds at mid and upper elevatons. Mark found plenty of evidence that winds had been at work in the Apgar Range and the Lake McDonald area: wind-packed snow and thin but sensitive slabs in usually sheltered areas, cornices at ridgelines, and snow plumes off the higher peaks. Another rider in John F. Stevens Canyon reported reactive wind slabs 10-14 inches thick above 7000 feet, with thinner and less reactive slabs at lower elevations. Elsewhere in the region, upper-elevation weather stations recorded 24-hour average wind speeds hovering just below transport thresholds (upper teens), with stronger gusts. The exception was Aeneas Ridge, which may be partially rimed. Similar winds are forecast for today, with a few inches more snow accumulating across the region. So the wind slab machine will keep running, with more snow to redistribute. Hiding out in terrain sheltered from the winds will provide the safest and best riding today, or sticking to lower-angled slopes where the near-surface snow is packed by the wind.

Monday night was an exception to the past few weeks of storms and clouds: mostly clear skies with some spotty valley fog. Favorable conditions for development of near-surface facets and/ or surface hoar. And indeed, that's what an observer saw on easterly slopes up to at least 5600 feet in the Swan Range Tuesday morning. It's not clear whether this layer is widespread in the region. Mark didn't report it in the Apgars, where he found the snow surface damaged by strong winds. The rider in John F. Stevens Canyon didn't note it either. No reports yet from the surface hoar factories in the Whitefish Range.  The snowfall forecast for the next few days will bury this layer before we get a clear picture of its distribution. Where it exists, freshly fallen snow may be more reactive a rider, so approach steep, sheltered, open slopes with caution. 

 

 

Regions covered