Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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

An Avalanche Warning is in effect in all zones of our advisory area. Warm temperatures and sunny skies will produce large and deadly avalanches. Avoid traveling in avalanche terrain today. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    The likelihood of spontaneous large and very large avalanches makes steep terrain and avalanche runouts very dangerous. Heat and radiation are destabilizing hard slabs perched on deeply buried weak layers. Debris from these slides can run the full length of avalanche paths, making surviving one of these events nearly impossible.

    Recent avalanche activity includes Wet Slab avalanches. This is a result of meltwater making its way down to buried weak layers. Regardless of the mechanism, the travel advice remains the same. Avoid all avalanche terrain today. 

    (3/17/2024)

    The darker-colored debris is a small portion associated with a hard slab avalanche originating on Nyack Mountain. It traveled nearly 3000' to the valley floor on March 16 and rests on an enormous pile of debris from a hard slab that failed on February 28 or 29. 

    Photo: Mark Dundas

  • Loose Wet

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

    Prolonged warming and solar radiation continue to cause large wet avalanches. Wet Loose and Wet Slab avalanches will occur on all aspects. 

    Mushy snow that does not support your weight or machine is a sign you could trigger a wet avalanche. Escaping a large wet avalanche is nearly impossible. Be aware of the terrain above you. In the past three days, wet avalanches large enough to bury a person have hit frequently used snowmobile trails. Avoid being on or under steep slopes.

    (3/17/2024)

    This long, thin pile of debris is courtesy of a finger of wet loose debris. The finger left a polished bed surface before coming to rest and depositing this lengthy, thin debris pile. 

    Photo: Mark Dundas

  • Cornices

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

    Impressive southwest winds built large cornices along alpine ridgelines in late February/early March. Intense warming is weakening these features. A failing cornice can send large blocks of snow trundling downhill, potentially triggering a destructive avalanche.

    The nature of this problem is highly unpredictable and should warrant your respect. Give these whales a wide berth above and below a corniced ridgeline to reduce your risk. Don’t get surprised by a cornice breaking further back than expected.

    (3/7/2024)

    A cornice fall in Rubideau Bowl in the Apgar Range just north of Apgar Lookout. This feature substantially  increased in size during the intense wind event of February 28 and 29. 

    Photo: Mark Dundas

Avalanche Discussion

The saga continues. Travel advice today is simple: Avoid avalanche terrain. Large avalanches continue to fail naturally. Although the brunt of natural activity is waning, destructive avalanches continue to occur. Here is an observation that paints a picture of recent avalanche activity. 

Overnight temperatures averaged in the low 40s and upper 30s at middle and upper-elevation weather stations. We are now approaching 90+ hours with above-freezing temperatures at mid and upper elevations. Warm temperatures and solar radiation are allowing melt-water to seep into the snowpack. This process is driving the avalanche danger today. 

So far, most of the observed avalanche activity has occurred on east-south-west facing aspects. Today is a candidate where we could see more avalanche activity on aspects that face north. Due to the amount of entrainable snow, avalanches that fail on north-facing slopes will be larger and more destructive than on south-facing slopes. Mark and Sarah found this slab avalanche in Rescue Basin on Sunday. This avalanche failed on an upper-elevation, northeast-facing slope. Continued warm temperatures are making avalanches like this more likely. 

Temperatures are forecast to drop below freezing tonight. The avalanche danger will rapidly drop once cooler temperatures refreeze the snow surface. Wintery conditions will return to the Flathead later this week. Expect a dramatic shift in avalanche problems. 

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