Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

An AVALANCHE WARNING is in effect. Multiple days of heavy snowfall and strong winds created very dangerous avalanche conditions.  Expect natural avalanches on slopes with active wind-loading and during periods of stronger snowfall in sheltered areas.  It will be very easy for you to trigger a dangerous avalanche.  Avalanches can be remotely triggered from flat terrain below steep slopes.  Travel in or below avalanche terrain is not recommended. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    2 to 4 feet of snow accumulated on widespread persistent weak layers such as fragile facets and faceted crusts.  Avalanches are propagating hundreds of feet wide and being remotely triggered from thousands of feet away.  This is not a manageable avalanche problem. Avoidance is the travel advice. Very large avalanches may run naturally today on heavily drifted leeward slopes.

    On Friday, this avalanche was 650 feet wide! No way you are riding out of that one. 

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Continual snowfall since last Thursday and produced some avalanche activity breaking in the storm snow.  On Sunday, observes noted an obvious layer of lower density snow 10 to 18 inches deep in the snow.  It was easy to trigger avalanches on this low-density layer but often avalanches broke deeper in the snowpack on facets or faceted crusts.  Even though you can trigger avalanches in the upper snowpack in the storm snow, the greater and more likely threat is avalanches breaking deeper into the snowpack (the Persistent Slab problem listed above).

     

    1/14:  Natural avalanche stopping just short of Kebler Pass Road.

    Photo: Eric Murrow

Avalanche Discussion

5 consecutive days of snowfall transformed the snowpack and landscape around Crested Butte.  It's wonderful to see big snowbanks around town but it comes at the cost of very dangerous avalanche conditions.  Recent observations tell the same story...natural avalanches, triggered avalanches, frequent collapses, and substantial storm totals.  A forecaster observation from Mount Emmons on Sunday described conditions as 'Unique and touchy' with triggered avalanches occurring in small openings in the forest.  Another forecaster observation from Kebler Pass documented a handful of natural avalanches impacting the road with one being large enough to bury a person.  The lack of visibility prevents observers from seeing the full scale of natural avalanche activity thus documented avalanches from the past few days have been skewed towards below treeline terrain and smaller terrain features.

A prolonged dry period during the second half of December which lingered until January 5th created widespread persistent weak layers in the snowpack (remember the Loose Dry or facet sluff problem).  Since January 5th, frequent storms began building slabs above this widespread weak layer culminating with an intense storm on Sunday and continued snowfall today.  In snow-favored areas of the Northwest Mountains, slabs have grown up to 40 inches thick (5 inches of snow water equivalent) in sheltered areas and much deeper on drifted terrain features.  In the Southeast Mountains, slabs above the persistent weak layer are commonly 2+ feet thick (3 inches of snow water equivalent) in sheltered terrain.  Although slabs are not historic in size, they are big enough to easily bury and hurt you.

For today, it's an easy choice to simply avoid entering or being below avalanche terrain.  When the storm ends tonight, the avalanche hazard will slowly improve, but human-triggered avalanches will remain a serious threat in the days to come.

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