Avalanche forecast

Whitefish Range

Flathead Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Very dangerous conditions exist at all elevations. Large natural avalanches are likely at upper elevations; debris from these slides may run to low elevations. Triggered and natural wet snow avalanches are also likely on and below steep slopes at low and mid elevations, making even small slopes dangerous. Avoid travel in the backcountry, including slopes adjacent to ski areas.

Avalanche problems

  • Wind Slabs

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

    Strong southwesterly winds have deposited slabs of new and drifted snow on leeward slopes at upper elevations. With more snow and wind forecast today and tonight, these slabs will continue to thicken. Natural avalanches are likely to release on the lee sides of ridges, peaks, and saddles at upper elevations, particularly near the crest of the Whitefish and Swan Ranges. Debris from these slides may entrain wet snow at mid elevations and run full track, into low elevation runouts. After temperatures drop this evening, more slabs will form at mid elevations. If you must travel in the backcountry, avoid avalanche runouts. 

     

    (12/25/2022)

    Triggered a small slab of drifted snow on a test slope. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3

    Over an inch of rain has saturated what was loose, dry snow at low elevations. Natural and triggered wet snow avalanches are likely on steep slopes at low and mid elevations. These may release near the ground and involve dangerous amounts of debris on even small slopes like cutbanks. Balls of snow rolling down a slope are a clear sign a slope has wet snow primed to release. Stay out from under slopes like these. 

    (12/26/2022)

    Recent wet loose avalanches along Highway 2 in the Middle Fork. 

    Photo: Adam Clark

  • Persistent Slabs

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

    Buried by the storm snow and wet snow of the past month are weak layers of facets, sometimes around crusts. These layers are being overloaded by the weight of recent precipitation and straining under the temperature-induced changes in the slabs above them. A rider's weight may be enough to tip them over the edge, producing large, dangerous avalanches the involve most of the season's snowpack. Natural avalanches that release near the surface of the snowpack may also step down to these layers, making for much larger, or destructive slides. These may be more likely in areas where the snowpack was shallower prior to the snow of the past week, such as sunny, windward slopes at mid elevations. 

    (12/22/2022)

    The crown of this large natural avalanche wrapped across terrain features and through burned snags on an upper elevation, southeast facing slope. 

Avalanche Discussion

Unless you're a glutton for punishment, it's not a good day to be wandering around the backcountry. Wet, windy, and very dangerous. And that follows several days of wet, windy, and dangerous. With more of the same on the way. It's a good day to spend time with family and friends, or tidy your garage. Maybe return that air fryer your aunt gifted you. 

As wet as it's been in the valleys since Christmas Eve, air temperatures at upper elevations have remained mostly below freezing, with strong southwesterly winds. Observers have reported blowing snow off ridgelines. The wind-blown snow has been deposited as thick slabs, particularly near the crests of the Whitefish, Swan, and Flathead Ranges. These slabs will grow today and tonight, increasing the likelihood of them releasing spontaneously and increasing the potential size of natural avalanches. Debris from these slides can entrain wet snow at lower elevations and run to valley floors. Avoid these runouts. Plumes of snow near ridges are clear signs of wind transporting snow above you.

Valley stations are reporting 0.7 to 1.5  inches of rain in the past 36 hours or so. That rain has fallen on a snowpack that, until Christmas Eve, consisted of dry, unconsolidated snow. Now it's what, in technical terms, is called mush. Gwanch. Or slop.And it's unstable, as evidenced by a wet loose avalanche that blocked one lane of Highway 2 near Stanton Creek Monday night, and avalanches reported near Marias Pass Monday.  The danger posed by these conditions continues today, though it will diminish after the cold front sweeps through tonight. Because wet snow avalanches may release near the ground, even small slopes and timbered areas can be dangerous. 

And then there are the weak facets buried Nov. 22 that produced triggered and remotely triggered avalanches the first week in December. Those facets aren't gone. They're undergoing all manner of rapid and unpredictable changes - rounding with the heat from the ground and rain, being strained by changes in the properties of the slabs above them, such as increased creep rates. The undertainty about these layers, including uncertainty about their distribution, is the key thing to keep in mind today. That uncertainty makes managing terrain and slope angles very tricky, because the likelihood of remotely triggering these layers may be increasing. The potential size of triggered and natural slides definitely has. 

And if that wasn't enough to keep you out of the backcountry.... We have reports of isolated glide cracks that have already formed, possibly because the ground wasn't frozen when the first snow fell. These cracks are likely to release with the warming and rain. One exists in Crown Bowl, in Noisy Basin. Getting buried by debris from a glide avalanche during the December holidays is not the way you want to make a name for yourself.

Sadly, the season's first avalanche fatality occurred Monday in Colorado. The avalanche caught four riders and buried two; one rider did not survive. The accident occurred on a steep slope within sight of a US Highway. Our hearts go out to the survivors, family, friends, and community of the victim. With the atmospheric river blasting across the western US, I fear this won't be the last this week. Don't make the news this way. 

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