Avalanche forecast

Southeast 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

There were numerous natural and skier-triggered avalanches involving storm instabilities yesterday.  In the Southeast Mountains, this threat is most pronounced at higher elevations, where winds are drifting the new snow into larger and more dangerous slabs.  Make conservative terrain choices where there is fresh wind loading and monitor for shallow storm instabilities at lower elevations.   Shallow or rocky slopes with variable depths have lingering concerns for avalanches breaking on deeply buried weak layers.  

Avalanche problems

  • Wind Slabs

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

    Up to a foot of recent snow and moderate to strong west/southwesterly winds are forming sensitive slabs at higher elevations.  Look for and avoid thicker drifts below ridges, in cross-loaded gullies, and below rollovers.  Cracking or collapses in the snow or blowing snow are signs of instability.   Avalanches could release naturally today due to additional wind loading.  

    An example of a storm instability triggered earlier this week.  Slabs are growing larger than this avalanche in drifted terrain now.  

  • 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.  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.

Avalanche Discussion

Observations yesterday were limited to near and below treeline slopes due to stormy weather and poor visibility.  The focus of storm slab activity was in or near the border of the Northwest Mountains, where favored storm totals are reaching 18"+.  I suspect there has been ongoing avalanche activity at higher elevations across the entire forecast area, because alpine winds have been blowing 20 mph, gusting to 40's and 50's since mid day yesterday.  All of these concerns continue today. With a downturn in snowfall today, storm slab instabilities in sheltered terrain are expected to be a bit quieter.  Regardless, be suspicious and defensive below treeline.  Where storm totals are more than about 8 or 10", use small, steep test slopes to gather information about how the storm snow is behaving before considering wind sheltered avalanche terrain.

During and in the wake of our last few storm cycles, avalanche activity on weak layers near the ground has significantly decreased, but not entirely gone away.  In the Northwest Mountains, the last few deep slabs failed on near and above treeline slopes with shallow and variable snow depths (Ruby Peak, Robinson Basin).    In the Southeast Mountains, the last few persistent slab avalanches were triggered from rocky terrain with variable snow depths, or in shallower parts of the zone where the snowpack is thinner (CBMR, Walrod).    Though the chances of triggering a deeper layer are relatively low, there appears to be more problematic slopes in Southeast Mountains because the snowpack has remained thinner and weaker there throughout this season.  Because the consequences are so serious, grab a black Sharpie and write the words "shallow, rocky, and variable" on your partner's forehead so you don't forget the most worrisome terrain.

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