Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

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

Enjoy today's sunshine while making smart terrain choices. Evaluate recently wind drifted snow where triggering a slab remains possible. Cracking and stiff, dense snow should steer you to sheltered slopes harboring safer and softer conditions. Choose planar slopes without exposed rocks or thin scoured areas to minimize your chances of triggering a slide on a deeply buried weak layer. 

Avalanche problems

  • Wind Slabs

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

    Thursday's storm deposited 6-12 inches of warm, wet snow above 5000 feet. This snow generally fell onto a crust or a thin layer of snow capping a crust. Winds blew at speeds strong enough to transport this snow during the storm and through Friday afternoon. Observations from Stevens Canyon reported 10-18" thick slabs on easterly aspects, and a report from the Middle Fork noted large swaths of wind-affected snow above 4500 feet in an open basin. Today, you can trigger a slide in areas harboring freshly formed slabs on typical leeward and cross-loaded slopes. Swirling winds may have left slabs in unusual, isolated locations in large open basins at low and mid elevations. Utilize hand pits and slope cuts on test slopes to determine how well these new slabs bond to the underlying crust. Shooting cracks should steer you to safer riding in sheltered terrain.

    (1/20/2022)

    Riders intentionally triggered this small wind slab on a NW aspect at 6000 feet.

    Photo: Rob Millspaugh

  • Deep Persistent Slabs

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

    We are listing Deep Persistent Slab as a problem for the first time this season. Please see the Forecast Discussion below for more information as to why. Potent storms on January 7 and 12 initiated large destructive avalanches that failed on weak faceted snow near the base of the snowpack in the Flathead Range and the Whitefish Range. This weekend's warming temperatures and sunny conditions make us wary of this Low Probability/High Consequence problem. The only way to know if the slope you are on harbors these layers is to dig to the ground. Even then, snowpack tests don't always give clear signals. We recommend using terrain to navigate this problem: Choose planar slopes free of convexities, avoid rocky areas where weak snow develops, and steer around thin wind-scoured areas in favor of slopes holding a deeper snowpack.

    (1/17/2022)

    Upper elevation, steep, rocky, complex-looking terrain is the common theme for locations where deep persistent slab avalanches failed on 1/12/22. 

    Photo: Mark Dundas

Avalanche Discussion

Thursday's storm was a welcome refresh until the temperatures warmed and the snow turned to rain at low elevations. Observations Friday noted a fresh rain crust up to at least 4500 feet and dense snow above that. The new snow was transported onto leeward aspects by southwest winds, with the BNSF avalanche team noting cracking in 10-18" wind slabs. An observer in the Swan Range reported pleasant Fist hard snow bonding poorly to the underlying crust. The FAC January intern toured in Cascadilla Creek in the Flathead Range, where he found large swaths of wind-affected snow along with recent avalanche activity. On the other end of the spectrum, an observer in the Flathead Range did not find evidence of slabs despite looking far and wide.

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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