Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Recent snow and strong winds have caused an uptick in avalanche activity at higher elevations over the past few days.  Several broad and destructive avalanches ran naturally from wind-loaded terrain on Friday and Saturday.  These avalanches exemplify our primary concern today, which requires conservative terrain selection to safely manage.     The threat of a dangerous avalanche is most acute in wind drifted terrain, but also exists in wind-sheltered terrain on the northern half of the compass.   

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    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 the recent wind has added more stress to slabs.  We have clear evidence of this problem from several destructive slides that ran over the past few days.  You can decrease your chance of triggering this avalanche problem 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

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Strong northwest on Friday formed dense and thick slabs of drifted snow behind leeward features.  We saw numerous natural wind slabs fail on Friday, and more human and explosive triggered wind slabs yesterday.  Although slabs are becoming harder to trigger now, they are thick and stiff enough to break above you and take you for a dangerous ride or bury you.  Give wind slabs more time to fully heal: Seek out softer, wind-sheltered snow and avoid steep terrain with signs of recent wind loading.  Wind slabs will look smooth and rounded, and feel denser than wind-sheltered snow.  Drifts will be located below ridges and convexities, behind tree fences, and in cross-loaded gullies favored by northwest winds.  

    3/11: A large, remotely triggered wind slab on Gothic Peak. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Just like yesterday, warming temperatures and sunshine could trigger wet loose avalanches on steep, sunbaked slopes today.  The problem will be obvious if it develops: you'll see rollerballs, pinwheels, or small sluffs starting to shed from very steep terrain and from below rock outcrops.  Use caution below steep gullies and above terrain traps once the snow surface starts getting sticky or gloppy.  Most wet loose avalanches should remain small in size.  If we see a greenhouse effect this afternoon, it could expand the distribution to low elevation northerly aspects as well.  

    A small wet loose avalanche that ran naturally yesterday from a steep, sunbaked slope.   

Avalanche Discussion

In today's headline news: very large avalanches have been failing from higher elevations.  From Park Cone to Scarp Ridge to Peeler Peak, we noted several D2.5 to D3 persistent slabs that failed during or in the wake of Friday's wind event.  The avalanche on Peeler Peak likely ran sometime yesterday, either from a cornice fall or a warming-related issue.  These avalanches are steering our avalanche danger and travel advice.  They are the result of our dry spell facet layer..."the sandbox layer"... getting incrementally loaded by snow and wind since mid-February.  Although slabs at higher elevations are thick and dense enough that triggering is becoming more difficult, the consequences are severe.  With more warming today followed by new snow and wind-loading tonight, the isolated potential for a destructive natural from this type of terrain continues.  

Despite continued snowfall all last week and daily reports of rumbling collapses below treeline,  we've only observed a few persistent slabs fail at lower elevations this month. Here are two examples (A, B).  It seems that the main driver for this contradicting feedback is the very extensive natural avalanche activity that effectively removed much of the slab structure on most steep below treeline slopes back in late February.  With careful snowpack and terrain assessments, you can travel below treeline with a relatively lower risk of triggering a deadly avalanche.  On those suspect northerly to east facing aspects, be especially wary of slopes that didn't avalanche in the past few weeks, particularly in the shallower parts of forecast area (Southeast Mountains).  

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