Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Persistent slabs are becoming increasingly difficult to trigger during our quiet weather pattern in the Southeast Mountains.  To guard against the possibility of triggering a large and dangerous persistent slab, choose routes that minimize exposure to shallow and rocky areas. Instead, target objectives with a deep (more than 150 cm) and uniform snowpack.  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.  Stay alert for fresh wind slabs forming above high-consequence terrain in the alpine.  

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Northwest winds are increasing to transportable speeds today at higher elevations.  Expect to encounter thin wind drifts forming below ridges and cross loaded features in the alpine.  Although they should be small and easy to skirt around, fresh drifts could be an issue if you get knocked over in consequential terrain such as above cliffs or gullies.  

    Example of a small wind slab in a crossloaded gulley on Gothic.  

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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 recent 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.

Avalanche Discussion

With an increase in wind speeds overnight and a couple of inches of fresh snow available for transport, we've relisted wind slabs as a developing problem.  Fresh wind slabs should be small and easy to avoid, but stay alert in high-consequence terrain.  

The sensitivity of persistent slabs continues to gradually decline under our relatively quiet weather pattern.  Explosive testing on windward aspects yesterday at Irwin did not produce results.  In the Northwest Mountains, the snowpack is deeper and stronger, and the threat of triggering a persistent slab is trending away.  We still have some isolated concerns for atypically shallow slopes where wind erosion or previous avalanche activity make it easier for riders to impact weak layers.  There's a significant change in snow depths and structures as you travel to the shallowest parts of the Southeast Mountains.  Yesterday, targeted stability tests near Red Mountain produced unstable results on both of our prominent weak layers in the lower snowpack.  Not all of the Southeast Mountains have such a poor structure; some areas have a deeper and more trustworthy pack as well.  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 goldilocks snow depth for finding the most troublesome structure seems to be around 3 to 4 feet (90 to 120 cm).   

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