Avalanche forecast

Southeast Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Wind-sheltered terrain with a deep and uniform snowpack offers the safest riding today.  Wind-drifted slabs have formed in leeward terrain at higher elevations, exemplified by several skier-triggered slides (Ruby, Schuylkill) and natural avalanches (Hunter Hill) on Wednesday.  In the Southeast Mountains,  triggering a large and dangerous persistent slab remains possible.  Be cautious in snow-deprived areas where slabs are only a few feet thick or in wind-affected terrain where slopes with a thin and variable snowpack are more common. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    In the Southeast Mountains, faceted weak layers are buried 2 to 6 feet deep and are becoming more difficult to trigger as layers adjust to the last month of active loading.  Slabs are most easily triggered where they are thinner, which is most common in shallow areas near Crested Butte and CB South, or in wind-affected terrain.   Be cautious of windward terrain features with variable depths, rock bands, and slopes where slabs are only a few feet thick.   The safest riding is where the snowpack is uniform and consistently deeper than about 5 feet (150 cm).  

     

    This large persistent avalanche was explosively triggered on Mt. Crested Butte on 1/17.  It exemplifies the destructive size, and one example of the type of terrain that is troublesome.

  • Wind Slabs

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

    Observers triggered a handful of fresh wind slabs 6" to 12" thick on Wednesday.  On Thursday, several recent natural Wind Slabs were viewed on Hunter Hill.  West winds are forecasted to increase later today accompanied by light snowfall, which will thicken recent slabs or form a fresh batch.  Wind drifts are most common below ridges, in crossloaded gullies, and below abrupt rollovers.  Be especially cautious in large or consequential terrain.  Cracking snow and blowing snow are signs of instability.  Most slabs are expected to be small, although there could be isolated exceptions in terrain with large fetches.  

    1/26:  A trio of recent Wind Slabs on the easterly alpine terrain of Hunter Hill.  The lookers right avalanche is large enough to bury, injure, or kill a person.

Avalanche Discussion

The danger level for the Northwest Mountains is MODERATE (level 2 of 5) due to the formation of wind-drifted slabs at upper elevations.  Slabs began forming around 2 days ago with observers on Wednesday reporting sensitive conditions on leeward terrain features (Ruby, Schuylkill).  In the Southeast Mountains, observers noted several recent natural Wind Slabs on leeward upper-elevation terrain that reached large size (Hunter Hill).  A layer of faceted snow from the recent cold, dry period may keep drifted slabs sensitive to the weight of a person, and with more snow/wind in today's forecast, Wind Slabs may incrementally increase in distribution and size.  Seeing blowing snow and feeling stiffer deposits of snow will help you identify the problem so you can avoid it.

The Persistent Slab problem, in the Northwest Mountains, changed in name today.  Forecast staff decided it was time to transition to a Deep Persistent Slab problem.  The nature of the problem has not changed much for roughly a week, but a new weak layer has formed at the surface due to the recent cold and clear weather.  Modest snowfall is in the forecast for the next week which may create the need to describe a new avalanche problem at the surface if slabs develop above the current weak snow surface.  Yesterday, a large avalanche was triggered with explosives, at the cat ski operation above Irwin, indicating that a very small chance lingers for deep failing avalanches in the Northwest Mountains. Travel advice remains the same; avoid areas that are shallower than average and littered with trigger points like cliffs, rocks, or sparse vegetation.  Favor terrain with a deep (greater than 5 feet) and uniform snowpack on planar slopes. 

In parts of the Southeast Mountains, it's an unhappier story, where the snowpack has remained thinner and weaker this season.    For example, stability tests near Red Mountain on Tuesday produced unstable results on both of our prominent weak layers in the lower snowpack, both at ideal depths for human triggering.   Although there's a lot of variability across the Southeast Mountains right now, stability involving deep layers is generally improving.  You'll want to assess each slope on a case-by-case basis.  This map of modeled snow depths around our forecast area paints a generalized picture of the deeper and more trustworthy areas vs. the have-nots.  The snow depth for finding the most troublesome structure seems to be around 3 to 4 feet (90 to 120 cm).  Portions of the Southeast Mountains with greater snow depths (areas bordering the Northwest Mountains or the heads of Brush and Cement Creek) still offer far more trigger points than terrain in the Northwest Mountains thus creating an increased likelihood of triggering a deep failing avalanche.

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