Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
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 as accumulating snow on Saturday and a strong wind event on Sunday create very dangerous avalanche conditions. The low-density new snow that has accumulated over the last 24 hours has created reactive dry loose and storm slab avalanches. These avalanches will accumulate additional mass where they gouge into the old weak snowpack, or become very large and potentially unsurvivable where they step down into deeper persistent slabs. Large to very large avalanches can release naturally, or be triggered from low-angle slopes connected to steeper slopes. You can find a reduced avalanche risk on lower-angle southerly facing slopes that don't have additional overhead hazards. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    Storm totals will be 15" to 25" by the end of Saturday. You can expect widespread dry loose and/or soft storm slab avalanche problems. Storm slabs will be the most reactive where they formed over a faceted snow surface, primarily on the northern half of the compass. These same soft slabs could also fail on lower-density snow around the compass. Both dry loose and storm slab avalanches could accumulate additional mass as they gouge into the old weak snow below and become much larger than expected. Where this avalanche problem overlaps with the persistent slab avalanche problem, a triggered avalanche could step down into deeper weak layers and become notably more destructive. 

    Storm slabs will grow in size at higher elevations and near ridgelines where previous wind-loading has occured. 

  • Persistent Slabs

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

    Persistent weak layers in the middle and at the bottom of the snowpack are being tested by the accumulating storm. Multiple extreme wind events this winter have made the snowpack structure highly variable from one slope to another, so expect widely varying conditions. The most reliable way to manage this problem is to choose slope angles less than 30 degrees with no overhead hazard.  Many southerly facing slopes lack this avalanche problem. A triggered avalanche on these deeper weak layers could become destructive and unsurvivable. 

    A widely propagating crown on Mt Owen that occurred earlier this winter. Similar destructive avalanches could release naturally or be human-triggered this weekend. 

Avalanche Discussion

There are 2 parts to the elevated avalanche danger and/or natural avalanche cycles this weekend. They are split between Saturday and Sunday.

Saturday: The new snow is adding volume to triggered avalanches, whether that avalanche is a sluff, soft storm slab, or deeper persistent slab. The first two avalanche problems will be the most common. We haven't reached the 1.5" SWE thresholds that we previously estimated needing to be met for HIGH avalanche danger in the NW Mountains. As of 5am, we were well short and in the .7 to .9" SWE range with another .3 to .5" SWE in today's forecast. The new snow entrained volume in triggered avalanches will be the most notable factor creating dangerous to very dangerous avalanche conditions across the forecast area, but we may not see a notable natural avalanche cycle that should accompany a HIGH avalanche danger rating.

Sunday: With large amounts of snow available for transport and a wind event moving through the area, I believe this is the day that we will see a natural avalanche cycle. Stay tuned on Sunday morning as the weather forcast contenues to be refined. 

Upcoming Outreach Events:  

Trailhead Day: Jan 24, Slate River, 10 am-2 pm.

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