Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Although the threat of triggering an avalanche is becoming increasingly rare, the resulting slide would be large and dangerous.  Near to above treeline slopes facing west to north to east with previous drifting are the most likely locations to find trouble.  Be cautious of rocky or wind affected terrain where slabs become thinner.  Terrain with clean runouts free of trees, cliffs, or gullies will be more survivable if you find an isolated instability.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    Slabs 1 to 4 feet thick exist over several persistent weak layers in the snowpack:  Weak facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem has been most common on northerly and easterly facing slopes this month and has also recently been active on westerly facing terrain. Although persistent slabs have become increasingly isolated and difficult to trigger, there are a few areas where you may be able to trigger a surprisingly large avalanche involving most of the snowpack.  Persistent slabs can break wider than you expect, and they can be triggered from flat slopes adjacent to steeper terrain. You can reduce your risk by traveling on slopes where the problem isn't highlighted above, or by traveling on smaller terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees. 

    This large persistent slab was triggered by skiers descending the ridgeline on the Aspen side of the Elk Mountains last weekend, 12/17.  

Avalanche Discussion

The avalanche danger continues its gradual decline under our current dry spell.  We've lowered the likelihood of persistent slabs to unlikely in the Northwest Mountains, which have been relatively quiet since a few large avalanches occurred 10 days ago.  The Southeast Mountains have seen a bit more action in the recent week, both from explosive-triggered slides at CBMR, and a few natural and triggered slides in the wake of the last storm about 5 days ago.    That last storm was a relatively modest 3" to 4" system, but relative to the total season snowfall, it was more significant in the shallower zone, especially with the accompanying winds.  In both forecast areas, poor snowpack structures still exist; without the added stress of snow or wind loading, the slabs start to find a temporary balance with the weak layers.  That pattern will reverse if the upcoming holiday storm delivers as forecasted. 

We've been slowly chipping away at the persistent slab rose to help highlight the terrain where you are most likely to trigger a lingering persistent slab instability.  Below treeline slopes came off the roses recently because they have been quieter in the past two weeks. However, there are still some isolated concerns on the northern half of the compass if you find a cohesive, supportive slab in very steep or unsupported terrain features like above cliffs.  In the Northwest Mountains, we also pulled the high southerlies off the rose; our targeted fieldwork (Ex A, Ex B) suggests the recent warm spells have provided enough strength to the upper snowpack to reduce (but not completely eliminate) our concerns.  In that terrain, if you're riding on a steep and recently drifted slope without stout sun crusts on the surface, you may have found one of those isolated exceptions.  Our more limited field data from the high alpine of the Southeast Mountains suggests that higher southerlies were more wind-drifted and less crusted, thus minimal changes to the rose at this point.  

Regions covered