Boletín de aludes

Bitterroot

West Central Montana Avalanche Center
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Peligro de aludes

Sat
Alta montaña
2 · Moderado
Límite del bosque
1 · Débil
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Wet snow avalanches remain possible today. If you find yourself in wet, mushy snow, or find a still wet snowpack under a crust, consider stepping back to lower angle terrain. 

Buried weak layers 2 to 4 feet deep still linger in dry snow on upper elevation north facing terrain. You are unlikely to see red flags like cracking or collapsing before an avalanche occurs in these areas. If you find weak, sugary snow with a slab above, avoid the problem by sticking to slopes under 30 degrees in slope angle.

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Wet snow avalanches remain possible today. Yesterday we entered a period of cooler weather, but after several days of sunshine and warm temperatures, the snowpack still contains a lot of heat and liquid water. It takes time for the snowpack to fully refreeze. 

    There is uncertainty about how well-frozen the snowpack will be today. Temperatures in the mountains have been near freezing under mostly cloudy skies since yesterday morning. Today, temperatures will climb above freezing again in many areas, and we could experience some minor greenhousing with mostly cloudy skies and light winds. 

    You could find crusty snow at the top of a slope and mushy, wet snow at the bottom. Additionally, even if the old snow surface is crusted, it doesn't mean that the snowpack is fully frozen and stable underneath. The snowpack could still be very wet below the crust, creating a concern for wet slab avalanches. Wet slab avalanches are highly unpredictable, but occur due to water percolating down through the snowpack and pooling on crusts and weak layers. Observers reported large natural wet slab avalanches in the Swan Range earlier this week. 

    If you find yourself in wet, mushy snow, or find a still wet snowpack under a crust, consider stepping back to lower angle terrain. 

    (3/20/2024)

    A natural wet loose avalanche from the last few days that gouged down to the ground on an upper elevation southwest aspect of Murphy Peak. 

    Photo: Arden Feldman

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2.5

    A mostly dry snowpack with poor structure still lingers on some upper elevation north facing terrain. The primary layer of concern is weak snow surrounding a crust in the middle of the snowpack. This problem has been unreactive and had not produced avalanches in weeks, until last week when a group of skiers triggered a persistent slab avalanche in the southern Bitterroot on a slope where a layer of especially weak surface hoar existed above the crust. Tragically, this resulted in an avalanche fatality. You can read the preliminary report here. 

    Today, you are unlikely to trigger a persistent slab avalanche, except on specific slopes where this problem is more developed. You will most likely trigger a persistent slab avalanche on convexities, rollovers, or near rock bands. Before triggering, you are unlikely to see obvious signs of instability, such as cracking and collapsing. 

    Identify this problem by digging in the snowpack. Look for a crust buried by 2-4 feet of snow with a thin layer of weak snow above or below the crust. If you find this, use slope angle to avoid the problem by sticking to slopes under 30 degrees in slope angle. If you choose to ride in terrain with this persistent weak layer, reduce exposure by choosing a smooth planar slope free of terrain traps or trees in the runout.

    A snow pit in the southern Bitterroot with poor snowpack structure. 

    Photo: Cam Mackenzie

Avalanche Discussion

Yesterday, we transitioned to a cooler and snowier weather pattern after a week of sunshine and warm temperatures. Yesterday’s snowfall was unimpressive but favored the Seeley Lake zone with 0.4” of SWE, or around 3 to 4 inches of snow at upper elevations. The Bitterroot and Rattlesnake zones only received 1 to 2 inches. Due to this, we removed the wind slab problem from today’s forecast in the Bitterroot and Rattlesnake zones and kept it for the Seeley Lake zone. You are most likely to find small wind slabs in the Seeley Lake zone today, but keep an eye out for small and isolated wind slabs in the other zones as well if you are traveling around at the highest elevations. If you see cracking in the new snow, avoid steep, wind loaded terrain. 

As with the weather, the snowpack is also going through a transition period. This creates significant uncertainty in the forecast. The snowpack is slowly refreezing, and some areas may be better refrozen than others. Even the more frozen areas may still have wet snow below the surface crust, leading to wet slab avalanche concerns. Wet slabs are highly unpredictable and almost always bring significant uncertainty to the forecast. Additionally, there is continued uncertainty surrounding the sensitivity of buried persistent weak layers on upper elevation north aspects. With all of this uncertainty, consider making more conservative terrain choices today, and be sure to assess the conditions where you decide to ride. 

Please help us reduce the uncertainty by submitting an observation and letting us know what you find out there today. 

Ski and ride safe!

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