Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

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

Large human triggered wet loose avalanches are possible on south and west aspects at all elevations. Roller balls, pinwheels, wet and unsupportable surface snow, and small natural wet loose avalanches indicate a larger wet loose avalanche may follow. Large human triggered wind slab avalanches are possible on north and east aspects at upper elevations. Red flags include cracking, collapsing, and recent slab avalanches. You could still trigger a large persistent slab avalanche on all aspects at upper elevations. You are unlikely to see signs of instability, such as cracking and collapsing, before triggering. You can reduce your risk by skiing or sledding in more simple terrain. You can avoid all avalanche problems altogether by sticking to slopes less than 30 degrees.

Avalanche problems

  • Loose Wet

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

    Large human triggered wet loose avalanches will become possible on sun affected slopes today. Cloud coverage will decrease throughout the day, and temperatures are expected to be warm, possibly reaching into the 40s at upper elevations. The wind will be very light which will add to the warming trend.

    Many previously solar-affected areas have some form of surface melt freeze crust. Today, that crust must break down before the snow can lose strength and lead to wet loose avalanches. If you find yourself in an area with strong sun holding fresh, dry snow, expect the snow to become wet more quickly.

    The typical progression of wet loose avalanches involves rollerballs and small point releases, leading to larger wet loose avalanches. If you encounter rollerballs, pinwheels, or small wet loose avalanches, expect larger ones to follow. If you find yourself in wet, unsupportable snow or see natural, wet loose avalanches, mark that as the time to step back out of avalanche terrain.

    Wet avalanche debris can travel far and fan out more widely than expected. Wet snow is heavy and can be more difficult to escape from. Even a small avalanche could knock you off your feet and carry you into hazards such as rocks and trees. It can also carry you into terrain traps such as cliffs and gullies. A sluff of wet snow can step down and trigger a larger persistent slab avalanche in areas with poor snowpack structure, creating a more consequential avalanche.

    (3/8/2024)

    We skier triggered this small wet loose avalanche on an upper elevation south aspect on Sanders Peak. Although it was small, it was easily large enough to knock you off your feet. 

    Photo: Arden Feldman

  • Wind Slabs

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

    Large human triggered wind slab avalanches are possible on leeward upper elevation slopes today. Many wind slabs are old, smaller, and more stubborn. However, expect larger and more sensitive wind slabs in the central Bitterroot, which received 8 inches of new snow in the last 48 hours.

    Wind slabs can be found on or just below the downwind side of exposed ridgelines, behind rocky outcrops, on rolls or convexities, or in cross loaded terrain features such as gullies. They can look smooth, rounded, and pillowy.  Snow will feel more dense and consolidated underneath your skis or sled than surface snow that has not been wind affected. It may even be hard and sound hollow, like a drum. Be on the lookout for rippled, uneven snow surfaces, indicating that wind has transported snow, and wind slabs may be lurking nearby.

    Red flags include cracking, collapsing, and recent slab avalanches. Cracks shooting out from your skis or machine clearly indicate that you've found an unstable slab; however, if the snow is very hard, you may not see cracking before it's too late. A wind slab avalanche could step down and trigger a larger persistent slab avalanche. Stick to wind sheltered slopes less than 35 degrees if you find signs of instability.

    (3/3/2024)

    Shooting cracks triggered in wind slabs on northeast upper elevation aspects.

    Photo: Payton Schiff

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    Although unlikely, you could still trigger a large persistent slab avalanche on all upper elevation aspects today. Various persistent weak layers are buried in the snowpack, with the most concerning layer being small facets above a stout melt freeze crust midway down in the snowpack.

    Recent snowfall and wind loading throughout the week have been adding stress and testing the strength of the buried weak layers. Today, warm temperatures and sunlight could cause persistent weak layers to begin losing strength. You will be most likely to trigger a persistent slab avalanche on convexities, rollovers, or near rock bands. Before triggering an avalanche, you will unlikely see obvious signs of instability, such as cracking and collapsing. Smaller avalanches, such as fresh wind slabs and wet loose avalanches, can step down and trigger a larger avalanche on persistent weak layers.

    Dig down into the snow, and if you find softer snow around hard crusts or loose sugary snow below a firmer slab, recognize the potential for a large and dangerous avalanche. Use your individual or group risk tolerance to dictate how steep of a slope you are willing to expose yourself to. You can reduce your risk by defaulting to shorter, planar slopes without convexities and rollovers and with runouts free of surface obstacles and terrain traps. Use slope angle to avoid the problem altogether by sticking to slopes less than 30 degrees.

    (3/10/2024) Photo: Payton Schiff

Avalanche Discussion

We are saddened to report an avalanche fatality near Lost Trail Pass in the Bitterroot zone. On Tuesday, March 12th, a group of backcountry skiers triggered a persistent slab avalanche on a north aspect around 8000 ft. One of the skiers was caught and did not survive. Our deepest condolences go out to the family, friends, and community affected by this tragic event. A preliminary report of the accident can be found here.

For this reason, we have returned persistent slab avalanches to the problem list. This avalanche failed in a layer of small facets buried 3 ft deep above a crust. There is some uncertainty around the distribution and sensitivity of the snowpack conditions under which this avalanche occurred. We remain confident, however, that you will most likely trigger a large and dangerous avalanche in more sensitive areas. These areas are typically near rock bands where the depth of snow is more shallow or on convexities and rollovers where there is heightened stress on the snowpack.

Today marks the beginning of a warm and dry high pressure system that will persist over the weekend. This will be very different weather from what we have seen throughout the week thus far. All three forecast zones saw precipitation and wind every day since Sunday. Below are SWE (snow water equivalent totals) for the week:

Seeley Lake (North Fork Jocko SNOTEL): 1.3"

Rattlesnake (Stuart Mountain SNOTEL): 0.8"

Northern Bitterroot (Lolo Pass SNOTEL): 0.9"

Central Bitterroot (Twin Lakes SNOTEL): 1.5"

Southern Bitterroot (Saddle Mountain SNOTEL): 0.4"

Lingering persistent weak layers and differing weather from earlier in the week make for a trifecta of avalanche problems today. Despite the springlike weather forecasted, don't be fooled into thinking we are well within typically stable Spring skiing and sledding. Before entering into an avalanche prone slope, take a moment to clear your head and assess the terrain carefully. Even a small avalanche can carry you into hazards such as rocks and trees, causing traumatic injury.

Please let us know what you're seeing out in the backcountry by submitting an observation. As we cannot be everywhere all of the time, community reports of weather, stable or unstable snowpack conditions, and avalanches are essential information for us.

Ski and sled safe!

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