Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

It remains possible to trigger a very large hard slab on shady aspects above about 6500 feet. In that terrain, there’s no surface crust keeping you from collapsing buried weak layers. Your safest option is to choose slopes with a thick, supportable crust and deep, uniform snow cover. Avoid steep slopes with cornices overhead. 

Problemi valanghivi

  • Persistent Slabs

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

    Weak layers formed in January sit below 3 to 6 feet of firm snow. An avalanche failing on one of these layers would be unsurvivable. Stick to slopes less than 35 degrees if you do not feel a supportable crust under your feet. If you choose to step out into steeper terrain, avoid slopes near rocky outcrops, with variable snow cover, or with cornices overhead. Cornice fall can be the trigger that sets off a big avalanche. Expose only one person at a time and keep your partners in sight.

    (3/9/2021) Hard slab avalanche broke on a convex, rocky slope, where winds had previously drifted snow.

Avalanche Discussion

The last reported slab avalanches ran 5 days ago on the weekend of March 6th. These were large and failed on deeply buried weak layers. They were likely the result of a prolonged period of above freezing temperatures and intense sun.

We’re still talking about those persistent weak layers buried in late January. They rest under 3 to 6 foot thick, hard slabs. They consist of sugary, faceted snow in open areas and feathers of surface hoar on shady, sheltered slopes. Snowpack tests continue to show that they can propagate a failure. The question is whether you can trigger them. That’s unlikely where supportable surface crusts keep you from sinking into the snowpack underneath. 

All the spring sunshine has left a thick melt-freeze crust on southerly slopes at all elevations. A freezing rain event the last weekend of February left a thin ice crust on shady slopes to at least 7200 feet in the Swan and Whitefish ranges. We don’t know of any crust on upper elevation, northerly slopes in the Flathead Range and Glacier Park. 2 to 4 inches of snow sits atop these crusts.  

Lastly, cornices and glide cracks will be a concern for the rest of the season. Both are more likely to fail during periods of intense sun and warm temperatures. It’s best to avoid traveling on slopes beneath these unpredictable hazards. Cornice fall can trigger a persistent slab avalanche.

Regioni coperte