Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
View on map

Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions continue at upper elevations. As you climb higher, you are increasingly likely to trigger large avalanches 1-4 feet deep. Swirling winds have left slabs in atypical locations. Watch for stiff surface snow that can crack around you. Stick to planar slopes free of rollovers. Look for soft, cohesionles snow on low-angled, sheltered terrain for safer, better riding. Extreme wind chill will amplify the consequences of even a small accident or equipment issue. Keep your trip short and simple.

Avalanche problems

  • Persistent Slabs

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

    A layer of weak snow crystals - surface hoar and sugary facets - is widespread at middle and upper elevations. The troubling layer is found 1-4 feet below the surface, atop the mid-January crust. It is responsible for the recent series of intentionally, remotely, and accidentally triggered slides. Avalanches failed on this layer as recently as Tuesday on NE and SW aspects at mid-elevations in Canyon Creek, in the southern Whitefish Range. Surface clues like shooting cracks and whumpfing noises may clue you into the danger. They may also come too late.  The same goes for stability tests. Given that uncertainty, work the terrain to your advantage. Stick to slopes 30 degrees or less that are free of convexities and aren't below steep start zones.

    (2/9/2021) Collapsing buried surface hoar. Mid elevations.

  • Wind Slabs

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

    Wind slabs and cornices have formed on steep slopes around the compass. Look for textured, stiff snow on usually windward aspects, or further down slope than is typical. The low-density surface snow is prone to drifting, so slabs will continue slowly building. Steer around dunes and slopes topped by cornices for a safer, more enjoyable experience.

    (2/2/2021) Drifting snow and cornices

Avalanche Discussion

Over the weekend of the 6th, natural and human triggered avalanches large enough to bury or kill someone occurred across the region. Tragically, a group of snowmobilers triggered one of these slides in the Swan Range Saturday, and one rider was killed. See the most up to date information on this accident here. Our condolences go out to all the friends and family of the victims of these tragic accidents. We thank the rescuers who accept large amounts of risk during these events.

The weak layers responsible for most of those recent avalanches are surface hoar and facets buried 1 to 4 feet deep. While these layers are widespread on most aspects above about 5,500 feet, they are more reactive on steep slopes and at upper elevations. The brunt of the slab-building snowfall ended on the 7th. Reports of avalanche activity also subsided under cold, relatively calm weather. Signs of the danger haven't vanished, however.  On Tuesday, I got shooting cracks, whumpfing noises, and triggered persistent slab avalanches on southwest and northeast aspects in the Southern Whitefish Range. Another rider who made it to upper elevations that day reported propagating test results on a south facing slope. There's probaby more evidence out there, but few people have been recreating since the temperatures plummeted, so we have few other recent observations.

Given the uncertainty and serious consequences of the current snow structure, the simplest way to enjoy the cold dry snow is to rely on the known quantity of terrain. Stick to slopes that aren't steep enough to slide, and aren't below slopes that are. Find wind-sheletered terrain that's not above terrain traps. 

The surface snow has been blower. That's not - completely - a joke. Even light winds have drifted the low density powder onto a variety of aspects. With an arctic intrusion, winds are often shifty, building slabs in exposed areas on atypical aspects. Cornices form along ridges. With the sunshine today, wind slabs and cornices that fail may trigger deeper persistent weak layers. In sheltered terrain that sees the sun, small loose dry sluffs may run in very steep terrain.

Arctic air and extreme wind chill values of -55F continue today. Careful decision making and conservative choices are required to manage the avalanche hazard. The consequences of getting it wrong can be deadly in the cold. 

We have a new blog post summarizing snowpack and avalanche conditions for the January 12 - February 11 period here.

Regions covered