Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

Mon
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Avalanche danger will rise to high by this afternoon.  Wet snow avalanches are likely today in sun-affected terrain. Avalanches are possible on northern aspects at mid and low elevations. Larger terrain or bigger slide paths have the potential to run far.  Once the snow becomes wet, travel in avalanche terrain is not recommended.

Poor snowpack structure with persistent slab potential remains in dry snow on northern aspects. 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.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–2

    Last night, most areas barely made it into freezing temperatures. Any refreeze is likely superficial and will break down quickly today. Wet snow avalanches are very likely.

    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.

    In isolated terrain today, wet loose avalanches have the potential to break out into a slab as they move down the slope. If you see this, be especially cautious around avalanche terrain.

    When dealing with wet snow:

    - Making conservative terrain choices when dealing with a warm, wet snowpack is essential.

    - Be alert for rapidly changing conditions. Morning is often faster and safer, so plan your day so you are out of avalanche terrain before the snow becomes wet and weak.

    - Aspect is important. Generally, southeast slopes warm and destabilize first, followed by the south and then the west.

    - Changes can occur quickly, sometimes as fast as minutes, but definitely within an hour

    - Avoid steep sun affected slopes with wet snow

    - Warm temperatures and sun can cause cornices to fail naturally, so be cautious of overhead cornice hazards

    - In the evening, even if temperatures are cool, it can take hours for the heat to escape the snowpack. Avalanche danger can remain elevated into the evening.

    (3/15/2024)

    Numerous wet loose avalanches on south and southeast aspects starting at upper elevations.

    Photo: Payton Schiff

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    A poor snowpack structure with facets surrounding a crust in the middle of the snowpack still lingers. This problem has been unreactive and had not produced avalanches in weeks, until this week when a group of skiers triggered a persistent slab avalanche in the southern Bitterroot in an area where the snow above the crust is especially weak.

    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 will unlikely 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.

Avalanche Discussion

Today will be another hot day, even warmer than yesterday. What is different today is the lack of cold temperatures last night. Mid-elevation stations hovered right at freezing last night, and in the Rattlesnake, upper-elevation weather stations stayed above the freezing mark. We still likely saw a superficial refreeze due to clear skies and radiation escaping the snowpack. Expect this refreeze to break down quickly today and the avalanche cycle to start earlier in the day than yesterday. For a deeper dive into the world of wet snow, check out this avalanche encyclopedia post.

We are trending towards conditions where wet slab avalanches are possible across the forecast area. This problem is most likely at upper elevations on sun-affected slopes, where melt water pools above the stout crust in the middle of the snowpack. Wet slab avalanches can vary from slope to slope as the timing and amount of meltwater affecting weak layers differ.  In the past few days, wet, loose avalanches from above initiated large slab avalanches in the northern Swan range, north of our forecast area.

 An avalanche fatality occurred on Tuesday, March 12th, in the southern Bitterroot. You can view the preliminary accident report here. A full report will be issued within the next 30 days. Our deepest condolences go out to the family, friends, and community affected by this tragic event.

Please let us know what you're seeing out in the backcountry by submitting an observation.

Ski and ride safe.

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