Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Mon
Alpine
1 · Low
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Traveling earlier in the day on the surface crust will decrease your risk of encountering loose wet instabilities. However, conditions can dramatically change if the sun makes an appearance. If you start sinking in the snow, plan your exit or move to more shaded areas. Minimize exposure to overhead hazards and be wary of shallow, rocky areas where you could trigger an avalanche on a buried weak layer.

Avalanche problems

  • Loose Wet

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

    Late-March sunshine is strong and can quickly melt surface snow. Recent observations report that most aspects and elevations developed moist surface snow. Today’s intermittent cloud cover should limit the impacts of this problem, but if you encounter wet snow on a steep slope, triggering a wet-loose slide is possible. Look for signs such as snow shedding from the trees or roller balls tumbling down slopes as your signal to move to less steep and/or more shaded slopes.

    This problem will develop most quickly when dry snow transitions to wet for the first time. Northerly slopes above 6500 feet are the most likely areas to hold dry snow. On other aspects, many of the slopes have been warmed by the sun and now have a surface crust that will delay the onset of wet loose activity. Given the tricky nature of predicting solar input and rising temperatures, have a backup plan if the weather is warmer or sunnier than forecasted.

    (3/30/2024)

    Wet loose debris that originated on an upper-elevation snowfield on Little Dog Mountain is visible. These slides traveled nearly 2000 feet.

    Photo: Mark Dundas

  • Persistent Slabs

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

    Triggering a large avalanche failing on buried weak layers 2-4 feet below the surface is unlikely but not impossible.  You can reduce risk by avoiding steep, rocky, heavily wind-affected terrain on shady slopes, where the weak layers are closer to the surface. In some locations, southeast aspects also contain a mix of crusts and faceted layers, so be aware of where you travel, especially in upper elevations.

    Avalanches caused by persistent weak layers release in surprising ways. Before triggering an avalanche, you may not experience snowpack collapsing or other obvious signs of instability. Choosing lower-angle terrain without convexities is the easiest way to manage this problem.

    (3/17/2024)

    This is a hard slab avalanche on Nyack Mountain that failed on a northeast aspect at upper elevations on March 16. This slide likely failed on a layer of facets above the early February crust.

    Photo: Mark Dundas

Avalanche Discussion

Yesterday’s observations (observation 1, observation 2) reported that as soon as the sun made an appearance, it quickly warmed the surface snow and brought a round of wet loose activity at mid and upper elevations. Overnight temperatures dropped below freezing, likely creating a surface crust on slopes affected by the sun. Today’s partly cloudy skies should slow the breakdown of this crust, but any afternoon sun will increase the chance of wet snow instabilities. 

Yesterday, the Northwest Avalanche Center reported an avalanche fatality caused by a cornice breaking beneath a rider on Mount St Helens. As a precursor to the spike in temperatures forecast for tomorrow (Monday), this is a tragic reminder of the dangers of cornice failure. 

Large cornices, as we observed yesterday in the Marias Pass area (photo), sit atop many of our steep alpine ridgelines. These features are unpredictable, so caution is advised. If you travel ridgelines, remember that they often break further back than anticipated. A tumbling snow mass caused by cornice failure can entrain large amounts of snow and trigger a larger avalanche on the slopes below. Pay attention to overhead ridgelines and limit the time you spend below cornices.

The best way to avoid these wet avalanche problems is an early alarm clock and an early exit. Monitor the strength of the crusts at the snow surface while you travel. If you break through the surface crust or sink into a wet, mushy snowpack, it is time to plan your exit or move to a more shaded slope.

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