Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

With up to 8" of new snow and gusty winds overnight, the danger remains elevated above treeline, where the threat of fresh wind slabs and destructive slabs that break several feet thick is most severe.  Near and below treeline, you can still trigger a deadly avalanche on the northerly and east aspects.  This snowboarder-triggered avalanche yesterday below treeline exemplifies our concerns.   Avoid wind-loaded slopes and carefully assess the snowpack before riding in wind sheltered terrain.  

Problemi valanghivi

  • Persistent Slabs

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

    On northerly and east aspects, you can trigger a dangerous slab avalanche that breaks up to several feet thick on weak faceted snow that was buried last month. Slabs can be triggered remotely from below or adjacent slopes. Collapsing and cracking are clear signs of instability, although direct feedback on this problem has become less frequent. The most concerning areas are where wind loading is adding more stress to slabs.  We have clear evidence of this problem from several destructive slides that ran over the past few days.  You can reduce your risk by avoiding those wind-loaded areas and choosing slopes angles in the lower 30-degree range or less.

    3/12:  A large persistent slab that likely failed on Friday night from wind loading.  

  • Wind Slabs

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

    A fresh batch of wind slabs formed above treeline and on some near treeline slopes last night.   Gusty winds started from the southwest and swung to the northwest with last night's 3" to 8" of snow.  Watch for relatively small fresh drifts below ridgelines,  convexities, behind tree fences, and in cross-loaded gullies.  There is still isolated potential to trigger a thicker and harder slab of wind drifted snow left behind by Friday's northwest winds, now disguised below the recent snow.    By riding in wind-sheltered terrain, you'll avoid this problem and find softer snow.  

    An example of a recent wind slab avalanche

Avalanche Discussion

The avalanche danger peaked sometime around Friday, when a week-long storm culminated with strong winds.  This system produced several destructive natural avalanches breaking 3 to 4 feet deep on our dry spell layer, along with dozens of wind slabs.  The danger has been gradually trending down with quieter weather through the weekend.  Last night's quick-hitting system briefly reversed that trend, with up to 8" of low-density snow favoring the Northwest Mountains and alpine winds gusting into the 40's.  The downtrend in danger re-establishes today as quiet weather takes hold for the next couple of days.    We are lowering the danger to MODERATE in the Southeast Mountains first.  Storm totals there were smaller last night, persistent slabs aren't quite as destructive in size, and we've seen less evidence of natural persistent slab activity in that zone (perhaps because weak layers in the alpine were more damaged by winds back in early February).  The larger avalanche potential and more snow loading last night will keep the danger elevated in the Northwest Mountains for another day. 

The downtrending danger signals a decreasing likelihood of triggering an avalanche. Unfortunately, the expected size of persistent slabs remains the same:  large enough to bury and kill you, or in some cases, large enough to snap trees or destroy a car.   That puts us in a tricky situation where you can ride in steeper terrain without getting feedback until you hit the wrong slope or wrong spot on a slope (watch this video of a triggered slide yesterday near Kebler Pass).  I remain untrusting of northwest to east aspects for this reason.  The string of avalanche accidents around the state in the past week, along with the fatality just north of the Colorado border yesterday, illustrate how our persistent slab problem is very capable of delivering surprises.  

Regioni coperte