Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

A stable weather pattern and growing confidence in conditions indicates avalanche hazards are isolated. Mid-elevation slopes sheltered from the wind and sun offer the best riding with the least exposure to these hazards. Less straightforward are steep, convex, upper-elevation slopes that collect drifted snow or harbor deeply-buried weak layers. 

Avalanche problems

  • Persistent Slabs

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

    Two deeply-buried persistent weak layers pose a lingering hazard on steep slopes, particularly those that have a convex profile and/ or variable snow depths. While you're unlikely to trigger an avalanche on either layer, any slides that do release will break 2 to 4 feet deep. The most straightforward way to avoid this hazard is to stick to lower-angled slopes - "Dad pow," some dads call it. 

    Stepping out blindly into steeper, more consequential terrain ups your chances for a dangerous surprise. Testing for the deeply buried weak layers (see discussion) can reduce your risk if you don't get any red flags - or don't ignore them. Slopes with runouts clear of gullies, rocks, cliffs, and trees can reduce the consequences of a mistake in your assessment.

    (1/1/2025)

    An unlikely but serious hazard today: a convex slope with terrain traps where a large avalanche broke on a lingering weak layer.  The crown is approximately 500 yards wide and located east of Peter's Ridge on the east side of the Swan. Crown depth is estimated to be between 2 and 4 feet deep and occurred during the recent record snowfall event.

  • Wind Slabs

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

    Remain alert for isolated slabs of drifted snow in steep, upper-elevation terrain. These may be on any aspect, thanks to variable wind directions the past few days. They should be confined to slopes downwind of open fetches and saddles, the tops of chutes, and the lee sides of exposed ridgelines. You might find a few small slabs cross-loaded into gullies well below ridges.

    Signs of these slabs include rippled snow surfaces, small dunes or drifts of dense, cakey-feeling snow, and thin, soft cornices. Slope cuts can be useful tests so long as you or your machine sink into the drifts rather than riding on hard snow. Cracks longer than a body length should stop you in your tracks.

    (1/4/2025)

    A crack longer than a body-length is a clear sign of a slab of drifted snow sensitive to your weight, and a hazard on steep slopes.

Avalanche Discussion

A "Stepping Out" mindset seems appropriate for current conditions. In the week since our last significant storm, the region has seen a remarkably sustained period of calm to light winds, cloudy skies, and light but regular snowfall. That's added up - 1 to 2.5 inches of SWE across the region, with Noisy Basin and the Swan Range favored. Observations have noted almost no signs of instability. The exception was Saturday, when the BNSF avalanche safety team reported two slides involving wind-drifted snow, one a large natural and one a small, intentionally-triggered slab. We've also had a few reports of natural loose snow slides. The caveat here is that visibility hasn't been great. 

A stable weather pattern and growing confidence in conditions is the combination that leads me to the Stepping Out mindset. That's not the same as a "jumping in blindly with both feet"  mindset. It means that observations consistently describe similar conditions, with no recent surprises or red flags. So it seems fitting to check out committing terrain carefully. Specifically, assessing your objective for isolated but stubborn Wind Slab avalanche hazards and two lingering but seemingly dormant persistent weak layers. 

The persistent weak layer closest to the surface and likely most sensitive to a rider's weight is a thin layer of facets above a hard crust that formed in mid-December. It appears to be the failure layer in several large natural avalanches in the Flathead Range during the late December storm, as well as at least one rider-triggered slab in the southern Whitefish Range. This weak layer seems more widespread on slopes that catch the sun, where the mid-December melt-freeze crust is harder. Deeper - a meter or more - is the layer of surface hoar and small facets buried 12/7. This may be the weak layer in a large slide with wide propagation in the northern Swan Range that likely occurred during the 12/30 storm. It's not the distinct grey stripe it was when first buried, and has not produced propagation in large column tests in the past week. It's more widespread on shaded slopes. 

If your risk tolerance is low, you can enjoy terrain with little exposure to avalanches and not worry about surprises. If your risk tolerance is higher, you might choose terrain with more exposure, either on the slope or overhead. Me, I'd dig and look for these layers before committing to any slope with nasty consequences - steep start zones, slopes connected to steep start zones, runouts with things that would hurt or bury me deeply, or windward slopes with variable snow depths. I'd be looking for a thin, soft layer of sugary snow above a crust or the distinct grey stripe of the 12/7 buried surface hoar. To step out, I'd need test results that left me with little to no uncertainty about the structure and stability of the slope. No propagation or sudden collapses in multiple tests. The sample size for our experiment would be one - me or my partner.

Most observations report rime or freezing rain crusts, though the thickness and distribution of these crusts has varied from drainage to drainage. The rime crusts developed in areas enveloped by clouds at the end of last week, so they tend to be higher in elevation. There seems to be little pattern to the distribution of the freezing rain crust. Presently, these affect the riding conditions, not the hazard. 

If skies clear today and temperatures warm to near freezing, southerly slopes might see some rollerballs of wet snow and isolated, small wet snow sluffs.

Avalanche Awareness Class Tonight: Monday, January 6, at Great Northern Cycle and Ski at 6:00 p.m. FREE!

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