Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Periods of sunshine today will cause the new snow at the surface to lose strength quickly. Triggering a wet, loose avalanche is possible in sun-affected terrain this afternoon. Watch for indicators that the snow is losing strength like large rollerballs, point releases, or fresh wet snow avalanches. If you see these, it is time to exit avalanche terrain for the day.

Lingering wind slabs are possible along ridgelines, especially on east aspects. If you see cracking around your skis/snowboard or find a firm slab at the surface, stick to slopes under 35 degrees in slope angle.

Lawinenprobleme

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    6-12 inches of new snow from the past week sits on top of a stout crust. It won't take much sun for this snow to become wet today and slide, especially with the smooth bed surface. Most areas will have a superficial melt-freeze crust this morning, but this will break down quickly once the sun comes out.

    The typical progression of wet loose avalanches involves rollerballs, and small point releases, leading to larger wet loose avalanches. If you encounter rollerballs or small wet loose avalanches, expect larger ones to follow. Remember that even small avalanches can have serious consequences in consequential terrain. 

    If you find yourself in wet, unsupportable snow or see natural, wet loose avalanches, it is time to step back out of avalanche terrain and be aware of what terrain is above you. You can also move to cooler, shaded slopes to find drier snow.

    (3/20/2024)

    Several natural wet loose avalanches from the last few days on the southeast side of Murphy Peak. 

    Photo: Arden Feldman

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Winds the past 24 hours have been generally light, but periods of gusty winds as a front moved through yesterday built soft wind slabs along ridgelines, especially on east aspects. Yesterday, observers noted cracking around their skis in their travels at upper elevation but no avalanches. Expect to encounter areas of lingering wind slabs that formed yesterday and although decreasing in sensitivity, are still possible to trigger. 

    We are not anticipating more snow transport today, as wind speeds are expected to be light, and snow densities are high enough now to prevent significant transport.

    Wind slabs can often be identified by their smooth, rounded appearance and form along ridgelines, in gullies, behind rocks, or on convexities. 

    If you encounter cracking around your skis or snowmobile or see recent wind slab avalanches, step back to terrain with a slope angle under 35 degrees. 

    (3/28/2024)

    I observed cracking in fresh wind slabs along upper elevation ridgelines. 

    Photo: Arden Feldman

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2.5

    Persistent slab avalanches remain unlikely, but high consequence if triggered. The primary layer of concern is weak snow surrounding a crust in the middle of the snowpack. This problem has been unreactive and not producing avalanches, except for one avalanche in the southern Bitterroot that resulted in a fatality.

    You will not see red flags like cracking, collapsing or whumfing before triggering an avalanche. Slopes with previous ski tracks are still suspect, and it is possible that the second or third skier on the slope could trigger the avalanche. The only way to identify this problem is to dig in the snowpack. If you find a crust with a thin (1cm - 3 inches thick) layer of weaker snow above or below it and a slab above, recognize the potential for a larger avalanche. If you want to avoid the issue completely, avalanches are unlikely on slopes under 30 degrees in slope angle.

Avalanche Discussion

Spring conditions can change quickly, especially in late March or April, when the sun's angle increases. With the increased heating comes more unpredictable storms and the ability to quickly heat the snow. As a result, it can feel like many avalanche problems are occurring simultaneously.

Today, wet snow is the primary concern. The new snow at the surface will heat up quickly and move easily on the smooth bed surface. That isn't to say that wet slabs are no longer a concern. Areas at mid-elevation still hold wet snow in the middle of the snowpack, and isolated areas could still produce a wet slab. Or, if the new snow at the surface becomes fully wet, a surface wet slab is possible.

For dry snow, wind slab is the concern at upper elevations, and as you come off ridgelines, this new snow will behave more like a storm slab. Travel advice remains the same, though: if you see cracking in the new snow or it feels slabby under you, avalanches are possible.

During yesterday's storm, there were periods of graupel. Graupel pools at the base of cliffs, steeper rock bands, or steeper terrain and can pop out as an isolated but deeper slab. Look in the snow, and if you find a layer of small ball bearings, this can be a weak layer for avalanches.

Today, deeper persistent slabs are the only unlikely avalanche problem. This is good because they are also the most unmanageable and destructive.

That is a lot of uncertainty for a forecast with multiple "possible" problems.  Most of the problems will be driven by what happens with the weather today. If the sun comes out, think wet snow. If it is cloudy and continues to snow, think wind slabs and dry snow.

Please continue to submit observations even as the season comes to an end. The information helps us finish our forecasting season and produce a general avalanche advisory for the spring.   Unfortunately, the time has come for the avalanche center to begin wrapping up operations for the 23/24 season. Thank you for another great season! Our last forecast of the season will be issued on March 31st, 2024. On April 1st, we will issue a General Avalanche Information product with general spring backcountry travel advice.    Unlike our Forest Service neighbors, we are a nonprofit avalanche center, and we do not have the resources to continue producing avalanche forecasts later in the spring. Please consider donating if you value our work and would like to see us grow and improve our products in the future. We’re already looking forward to next season - let’s hope it’s snowier than this one! 

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