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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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The primary concern remains the lingering hazard of triggering slabs that break 1 to 3 feet deep on weak layers buried in late January. We've seen an unusual string of near-misses and accidents the past two weeks; the danger of more accidents is diminishing but not gone. You can find great riding and safer riding on sheltered, low-angled slopes that aren't above terrain traps. At the highest elevations, beware of freshly-formed slabs of drifted snow. 

Avalanche problems

  • Persistent Slabs

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

    When dealing with a Persistent Slab avalanche hazard, less feedback doesn't mean less danger. It means more uncertainty. The number of slopes where you can trigger a slab that breaks 1.5 to 3 feet deep is diminishing. Determining which individual slopes remain dangerous is difficult, however. You can navigate this connundrum by sticking to terrain where you're least likely to collapse any lingering facets or surface layers. If you're above about 5500 feet, that's slopes less than 30 degrees. Riding slightly steeper slopes adds more risk, so pick lines that avoid likely trigger points, like convexities where slopes steepen abruptly. And lines that aren't above terrain traps, so you minimize the consequences of a mistake. Tactics like this don't add much insurance on slopes steeper than about 35 degrees, where collapses can propagate quickly and widely, releasing slabs that are too wide to escape.  Slopes that face northwest through northeast to southeast have seen the majority of accidentally-triggered slides and near-misses the past few weeks. We've had no incidents reported from south- and west-facing slopes, or slopes below about 5500 feet.

    (2/15/2021) Skier-triggered avalanche crown from 2/15. Crown was 2 feet thick and ran roughly 1000 feet. SE aspect at approximately 6500 feet, northern Whitefish Range.

  • Wind Slabs

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

    Small, soft slabs of drifted snow pose a danger near summits and on the lee sides of ridges at upper elevations today. These are confined to the terrain most prone to catching wind-blown snow, and they'll be stubborn. They can, however, be dangerous on steep slopes above terrain traps like trees, rockbands, and gullies. Avoid slopes steeper than about 35 degrees with fresh deposits of drifted snow a foot or more deep.

    (2/19/2021) The varying depth on this triggered slide is typical of slabs composed of drifted snow. It's easy to underestimate how thick and wide they can break.

Avalanche Discussion

Friday's observations included reports of small triggered slabs that broke in the new snow with ski cuts at Whitefish Mountain Resort, and two small slides also triggered by ski cuts in John F. Stevens Canyon. The latter two appear to have involved freshly-drifted snow, though one may have broken deeper on buried persistent weak layers. Reported test results were inconsistent - propagation with easy force in the Skyland area (5600 feet, northwest), and no propagation on east and northeast aspects in Stevens Canyon at sites where tests a few weeks ago produced propagation, and ridge-stomping triggered a series of remotely-triggered slides. An observation from sunny slopes in the southern Whitefish Range noted no red-flag signs of instability. 

Combined with observations from earlier this week, it's clear that the trends are decreasing sensitivity of slabs and less widespread hazard. For individual slopes, however, there's more uncertainty. The one you're looking at might be more stable than it was a week ago. Or it might be one you could still trigger. There's nothing you can do to prove one scenario or the other, except gambling with your life or the lives of your partners. Digging a pit and testing? You might be too high on the slope, and the results can be misleading. You might trigger a slide well below your profile site, where the surface hoar was better developed and better preserved. 

There is one certainty with persistent weak layers, like the weak facets and preserved surface hoar buried in late January. They are far more likely to collapse and propagate a failure on slopes steeper than about 35 degrees. And slope angle is measureable. Less certain but typical of these layers is a propensity to break much wider than expected and to break across terrain features. That characteristic tends to magnify the consequences of a mistake. 

Solve this complex situation with the simple strategy of avoiding steep, consequential terrain for a little while longer. Stick to slopes less than 30 degrees if you want a wide margin for error, those less than about 35 degrees if you're inclined to take more risks. Ignore any FOMOP (Fear of Missing Out on Powder); there's plenty of great riding on moderately angled slopes, and really, do you grin dramatically less on a 30 degree slope than on a 35 degrees slopes?

Based on observations from Friday, the day's winds weren't strong enough or sustained enough to blow much snow around at mid elevations or just above. Any slabs of drifted snow at these elevations will be isolated. They'll be more common as you climb higher, so be alert for cracking in dense pockets of drifted snow or for the surface sings of recent drifting: fresh cornices, wind-scalloped snow surfaces, and smooth, lens-shaped dunes.

Pro tip: If you haven't taken an avalanche class in the past five years, consider taking a refresher. A multi-day course might be the most useful. You'll get some fresh ideas for using your experience to ride safely in unusual conditions. Or consider a Companion Rescue class, where you can practice the skills that you haven't had to use. Use our course list or education calendar to find one that fits your schedule. 

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