Bollettino valanghe

Seeley Lake

West Central Montana Avalanche Center
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Pericolo valanghe

Fri
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Dangerous avalanche conditions will develop today. Heavy snowfall and sustained winds continue to impact the area and build storm slabs across all elevations and aspects. Natural avalanches are likely, and human triggering is certain. Avalanches can step down to faceted layers at the base and mid snowpack, resulting in large unsurvivable avalanches.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Certain
    Dimensione
    1–2.5

    Today, storm slab avalanches are likely on all aspects and elevation across the forecast area. Rapid loading, rising temperature, and wind loading will cause storm slab avalanches. Natural avalanches are likely, and human triggering is certain. Heavy snow will fall atop low-density snow that fell yesterday creating the perfect recipes for avalanches. Storm slabs could be up to 3 feet deep. 

    Avalanches may run long distances. Travel in avalanche terrain is not recommended.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    Today, natural or human-triggered avalanches have the potential to step down to the layer of depth hoar in the southern Bitterroot on shaded aspects above 7400 feet. We don't know how much load it will take to fail, but the results will be large unsurvivable avalanches. Avalanches could fail up to 4 feet deep.  

    Frigid temperatures this past week continued to weaken the layers at the base of the snowpack, especially where the snowpack is shallow and where facets already exist. Large cornices falling onto slopes, as we saw on Dec. 22nd, and smaller slab avalanches running downslope can trigger deep, persistent slab avalanches.

Avalanche Discussion

The powerful storm impacting the forecast area is both dangerous and interesting. It's interesting because the dichotomy of a significant atmospheric river (fancy term for a large warm wet storm with a narrow corridor) butting heads with an arctic air mass is complex for weather models to nail down the exact impacts. However, we know that significant snowfall will occur across the forecast area along with increasing temperature and snow levels. 

Winds are forecast in the light range with strong gusts out of the west. Expect somewhere between 2 to 3 feet of snow in the next 24 hours for mountains throughout the forecast area. Valley bottoms could see up to 1 foot of snow. Rain is also possible below 6,000 feet. 

Colder temperatures and clear skies last week likely contributed to the further metamorphism of our mid and basal snowpack. Faceted layers mid snowpack have been identified in many areas across the forecast zone. One example is buried surface hoar atop the dense wind-packed surfaces from last week, 8 to 14 inches deep. Today, storm slabs could easily step down and effortlessly release on these layers, making for dangerous avalanches. These avalanches may have the potential to propagate long distances. 

Suppose you see avalanches from completely safe areas, far from potential runout zones or slopes steeper than 30 degrees; feel free to send pictures and notes our way at https://missoulaavalanche.org/submit-an-observation/. But please do not travel in on or near avalanche terrain today. 

Ski and ride safe

 

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