Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
4 · High
Below
2 · Moderate
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Highlights

Multiple days and nights of above-freezing temperatures are creating dangerous avalanche conditions. Large wet avalanches can occur on all aspects. Avoid being on or underneath any steep slopes today.

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3.5

    Expect all flavours of wet avalanche today. We’ve listed wet slab as the primary problem because it has the potential to do the most damage. As liquid water moves through the snowpack, it pools on pre-existing weak layers and buried crusts. This increases the likelihood of both human-triggered and natural avalanches, both of which are likely today. The best strategy is avoidance, by staying off of slopes with wet snow. Observers at Lost Trail saw at least one large natural wet slab avalanche yesterday.

    Wet loose avalanches and cornice falls could act as natural triggers for a very large wet slab avalanche. Both of these avalanche problems are also dangerous in their own right.

    Wet Loose: Wet loose avalanches are likely on all aspects at middle and upper elevations, specifically on very steep slopes (over 35-38 degrees). At lower elevations they are possible on very steep slopes where snow is continuous. We received reports of wet loose avalanches on all aspects in the Bitterroot yesterday.

    Cornice: Cornices grew large during last week’s storm. They are becoming increasingly fragile as warm temperatures add liquid water to the snowpack.

    Glide: New glide cracks are opening in the Bitterroot, and we’ve seen evidence of recent glide avalanches. Glide avalanches are incredibly difficult to predict, and are most likely to occur when liquid water is actively moving through the snowpack, as it is today.

    Stay off of steep slopes (over 30 degrees) where you find wet snow, which will likely be everywhere. With large natural avalanches likely, avoid avalanche paths and run-outs. If you do cross run-outs, do so as low as possible and go one at a time. Stay well away from slopes overhung by cornices or with open glide cracks. If you’re travelling at ridgetop, remember that cornices can break much further back than you expect.

Avalanche Discussion

There’s no getting away from it – the snowpack is wet. All warming related avalanche problems should be on your mind today. This includes wet slab, wet loose, cornice, and glide. Wet slab avalanches will be the largest and most dangerous of the set, and they are what’s driving the danger rating.

In the Bitterroot, compared to other ranges, there are more well-developed weak layers, plus we'll see higher temperatures and more sun today. This is particularly true for the southern Bitterroot, and explains why the Bitterroot is at High Danger, while the Rattlesnake and Seeley Lake are at Considerable. Regardless of danger level, any wet slab avalanche will be large and destructive. If the forecast clouds do not appear, danger could climb to High in all ranges during the hottest part of the day.

Travel advice is simple - stay off of steep slopes and give avalanche run-outs a wide berth. Fortunately the skiing and riding conditions are challenging right now, so temptation is limited.

Please send us any observations, even if it’s an avalanche you see from a distance while driving on the highway. Predicting the exact timing of a wet slab cycle is near impossible, and we have high uncertainty regarding exactly when wetted weak layers will “wake up.” Even one avalanche observation can help us rein in uncertainty and produce a more accurate forecast with more timely travel advice. We appreciate each and every observation you send us.

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