Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger remains elevated due to recent snow and wind. Expect to find fresh slabs of snow that increase in thickness with elevation. These will be more widespread and dangerous downwind of saddles and ridgelines or on cross-loaded slopes. Cracking is a sign of instability. It remains possible to trigger a large destructive avalanche on buried weak layers. Refrain from recreating on slopes steeper than thirty degrees or those connected to steeper terrain above.

Avalanche problems

  • Storm Slabs

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

    We have been blessed with recent quality snow, which has improved the riding. However, new snow and wind have formed thin slabs susceptible to human triggering. These will be thickest in areas where the wind has drifted snow onto leeward or cross-loaded slopes. Winds are expected to increase through the day so look for blowing snow as you gain elevation. Shooting cracks are a sign of instability. Sheltered terrain will offer a respite from the wind and slabby conditions. A slide in the new snow can trigger a much larger slide on buried weak layers. Continue to practice terrain management by choosing slopes less than 30 degrees in steepness and free of convexities.

    (2/25/2021) Wide-breaking wind slabs

  • Persistent Slabs

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

    Weak layers buried three to six feet deep were responsible for large to very large natural and explosive triggered avalanches Tuesday and Wednesday. It's becoming more difficult for a person or their machine to affectthese layers. Don't expect to receive feedback from them, such as collapsing or whumphing. Digging down to the January 13 crust is the only way to identify if these layers are present. Please continue to give slopes steeper than 30 degrees a wide berth while waiting for these layers to strengthen. Make sure the slope you are planning on riding is not beneath or connected to avalanche terrain. Continue to steer around convexities where you are most likely to affect a buried weak layer.

Avalanche Discussion

What a week! Bountiful snowfall significantly improved the riding conditions and gave us hope that the remainder of the season will be excellent. This same snow, plus a whole lot of wind, triggered impressively large Persistent Slab avalanches across our area. The results from small explosives used for mitigation in John F. Stevens Canyon confirmed that conditions were primed for avalanche activity. Amongst all of this activity, I noted a recent Glide Slab avalanche in the Swan Friday. I have been so focused on buried weak layers that I nearly forgot that we need to be aware of The Brown Frown.

You may have noticed that we dropped the hazard at middle and low-elevations today, along with trimming the distribution of the storm slab problem.  Storm slabs generally heal or stabilize within a couple of days of formation, especially if they are thin, like those developed at lower elevations or areas not affected by the wind. Friday, near treeline, I found no evidence of storm slabs in the Swan Range while Blase noted "just slabby enough" conditions in the Apgars. The Patrol Fund Level Two avalanche class, outside the boundary of WMR, found little evidence of storm slabs during their travels and in numerous pits on various aspects. While we have not received recent observations from upper elevations, we assume the amount of new snow and wind has formed storm slabs that are still reactive to a rider's weight.

Today we also dropped the likelihood of the Persistent Slab problem from reactive to stubborn. Unfortunately, it is not because the buried weak layers above the January 13 crust magically gained strength overnight. We have listed this problem as reactive for most of the week due to new snow and wind stressing the snowpack. We were also aware that new snow avalanches at the snow surface could step down to a buried weak layer. We are not expecting natural activity today, and the snowpack has had a bit of time to adjust to this week's heavy loading.  With that said, the Persistent Slab structure remains on many slopes and continues to show concerning results in snowpit tests. Friday, the Level Two class (Example one, two, three) found the weak layer of buried surface hoar reactive in Propagation Saw Tests. We remain wary of any slope steeper than 30 degrees, and encourage you to enjoy the great new snow on terrain that is not connected to avalanche terrain. 

You can watch our most recent weekly summary and weekend outlook video in our media gallery or here. 

Pro tip: Set boundary rules for the day and sticking to them. Define no-go terrain before you start your field day based on the avalanche and weather forecast, your gut feeling, and looking at the big picture that the riding season is a long one and it is just one of many. Thinking about friends and loved ones doesn't hurt either. Friday, my field partner and I made a plan that ruled out a steep short pitch that would have to lead us to a cool ridgeline and a host of riding options. We also ruled out steep awesome old-growth slopes. Once we were on the scene, both of those options were tempting, especially with the wonderful new snow. Our pit results were not alarming, but we had made a plan, and we were going to stick to it and not fall victim to powder fever. We both had a great day of low-angle riding, and I'm looking forward to getting out the next few days and repeating this process.

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