Bollettino valanghe

Snake River Range

Bridger-Teton Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
1 · Debole
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In sintesi

Dangerous avalanche conditions exist on steep slopes where it is possible to trigger a hard slab avalanche that is 2 to 4 feet deep failing on buried weak snow. This weak layer exists on slopes above 8,000 feet that face west through north through east. Avalanches can be triggered from a distance, so your best strategy to deal with this problem is to avoid being on or underneath steep slopes where the persistent weak layers exist.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–3

    In the last week there have been numerous avalanches that have failed on weak snow formed in January. This weak layer exists above 8,000 feet on slopes that face west through north through east. These are hard slab avalanches, breaking 2 to 3 feet deep, that can be triggered by the weight of a rider, or from a distance, so give steep terrain a wide berth. Even smaller slopes around creeks and in the trees can produce avalanches if they are steep. As we move farther away from the last loading event, signs of instability such as cracking or collapsing may not be present, but consequences are still high. Avoidance is the best way to deal with this problem as persistent slab avalanches are not manageable. 

    Watch for pockets of unstable snow in the higher peaks where shallow wind slabs may have formed.  A small avalanche failing near the surface has the potential to step down into buried weak layers, becoming large and unmanageable. Also, solar gain and warm temperatures could create shallow wet snow avalanches on steep southerly slopes. Take this into account in your travels today.

    Large natural persistent slab avalanche that happened around the last storm.

    While it isn't likely a natural avalanche will occur right now, the weight of a rider could trigger an avalanche on this scale.

Avalanche Discussion

During January and the early part of February, we received almost no precipitation or stormy weather. This led to many south facing slopes melting and becoming crusty, and shaded northerly slopes to weakened, developing surface hoar and weak faceted snow. When weather and snow finally did arrive it preserved these weak layers. Now the snow and water weight from our past 3 storms in February has put a slab on top of the weak snow, creating the perfect recipe for persistent slab avalanches.

Since this weak snow connects across terrain features, from the flats onto steep slopes, avalanches can be triggered from a distance (remotely triggered), meaning you don’t have to be on a slope for the weight of a person to collapse the weak layer, and connect to surrounding slopes. This is a dangerous setup and means we need to be really cognizant of the slopes we are traveling on, but also underneath.

As time goes on, the snowpack  may “feel good,” meaning it isn’t collapsing or “whoompfing” underneath us, and the riding is good. But, the weak snow hasn’t gone anywhere and can still produce dangerous avalanches. There is still great riding to be had, it just requires discipline in terrain selection. Slopes over 30° that fit the aspect and elevation of the persistent slab avalanche problem are where people could get into trouble. Thanks to the parties that have submitted observations over the last week! These observations are key in facilitating accurate avalanche forecasts. If you see anything, please consider submitting an observation here.

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