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

Stable weather continues strengthening recently formed slabs but triggering a slide in the wind drifted snow remains possible. Look for evidence of wind-affected snow as you gain elevation - pillows, textured surfaces, and stiff, dense snow. Cracking at the surface is a clue that you've found unstable snow and directs you to seek out areas sheltered from the wind. Choose planar slopes free of convexities to minimize triggering a deeply buried weak layer.

Avalanche problems

  • Wind Slabs

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

    Reports of wind-affected snow continue to trickle in. A party in the Flathead Range intentionally triggered a small 8-inch thick wind slab at mid-elevations Saturday while a group in the Swan found plenty of thin unreactive slabs. Slabs formed from Thursday's storm are becoming more stubborn to triggering but should remain on your radar. You can find these in the usual spots - downwind or leeward of saddles, ridgelines, and in cross-loaded gullies. They may have a pillowed smooth appearance and feel dense and stiff. Utilize hand pits and small test slopes to see how well they bond to the layer beneath them. Default to slopes sheltered from the wind for a safer, softer experience. 

    (1/21/2022)

    Fresh wind slabs were 10-18 inches thick on leeward slopes in John F. Stevens Canyon. These cracked under the weight of a skier.

    Photo: Adam Clark

  • Deep Persistent Slabs

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

    Weak snow near the snowpack base was the failure layer in a handful of large avalanches initiated by a wet, warm storm on January 12. These deeply buried layers could awaken from a surface slide, a cornice trundling down the slope, or solar input and warming that destabilizes these layers. Areas most susceptible to triggering are where the snowpack is shallow - wind scoured slopes, terrain peppered with rocks, or sunny aspects at mid-elevations. Steer around mid-slope convexities in favor of planar slopes and choose slopes with clean runouts to mitigate this hazard.

    (1/18/2022)

    This persistent slab avalanche initiated around 5800 feet on a southeast aspect in the Southern Whitefish Range. It ran during the most recent storm on 1/12/22.

    Photo: Rick Ziegler

Avalanche Discussion

Observers found various conditions Saturday that ranged from a few inches of snow from Thursday's storm with minimal wind effects at 7500 feet in central Glacier Park to 14" of recent snow and plenty of wind-affected surfaces in the Swan Range. The Swan folks found the new snow right side up and bonding well to the underlying crust with wind slabs thin and unreactive. Reports from the Flathead Range mentioned north-facing sheltered terrain holding dry surface conditions unaffected by the wind but yesterday's sun starting to warm and wet east-southeast aspects. Another observation from the Flathead Range noted variable wind affected snow in open terrain, which kept the skiing funky. Blase was in Canyon Creek with the Flathead County and North Valley Search and Rescue teams Level 1 avalanche class field day. They viewed 2 large avalanches in south-facing terrain from Thursday's warm wet storm, and their snowpits revealed a strong snowpack on a northerly slope at mid-elevations. 

We've listed Deep Persistent Slab avalanches as a problem for the first time this season. It's a low-likelihood, high consequences hazard. It can be difficult to manage, especially after seven weeks in which our primary hazards have involved surface layers in the snowpack that haven't produced many large avalanches.

Several factors prompted the decision. Primary among them was a natural cycle of scattered large and very large (D2-3) natural avalanches that released during last week's warming and rain (Whitefish Range, Flathead Range). These avalanches involved hard slabs (1 finger or harder) of both storm snow and old snow. They broke on weak layers near the base of the snowpack. We'd had few if any, reports of similar slides prior to these events, though several very destructive natural avalanches released in nearby Waterton Park, the North Fork of the Flathead, and the Lizard Range about the same time.

Consider these avalanches' public service announcements. The message? On isolated slopes, basal weak layers and hard slabs can still combine to produce deadly avalanches. So why now? The forecast for the next few days and possibly the next week calls for near-freezing temperatures and extended periods of partly to mostly sunny skies. The burst of energy into the snowpack may destabilize layers that have been quiet until now.

These slides are unlikely to release on most slopes. The isolated exceptions are slopes steeper than about 35 degrees where the snowpack is shallow or pock-marked with shallow spots. Snowpacks like these may exist in unusual locations - sunny slopes or around rocky, mid-slope convexities. Search the terrain above and below you for slopes like these, and avoid them.

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