Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

In sintesi

Over a foot of recent snow accumulated in the Northwest Mountains.  You can trigger avalanches in the storm snow on steep slopes in sheltered and drifted locations.  Some storm snow avalanches could grow large enough to bury you.  A small chance remains for you to trigger an avalanche that fails deep in the snowpack from shallow areas where slabs become thinner.  Reduce your risk by choosing slopes less than 35 degrees where you encounter around a foot or more of new snow, where you find recent drifting, and where cracking in the storm snow occurs.  

 

 

Problemi valanghivi

  • Storm Slabs

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

    Over a foot of new snow accumulated in the Northwest Mountains with a few additional inches forecasted for daylight hours on Monday.  Reports from the Irwin area on Sunday indicated easy-to-trigger storm snow avalanches near treeline.  Prior to the storm, several observations mentioned surface hoar formation at a variety of elevations which may help create instability immediately beneath the new snow.  Look for cracking, utilize test slopes, and frequent hand tests to help understand the reactivity of the storm snow.  Areas with around 12 inches or more of new snow will indicate the increased hazard and need for increased caution.

    An example from a few days ago of an avalanche releasing in storm snow.  In this example, the avalanche failed in drifted storm snow but for today, expect similar storm snow problems to exist in sheltered areas as well.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    Slabs ranging from 5 to 8+ feet thick have formed around much of the compass and at all elevations over faceted weak layers in the lower snowpack. These weak layers have adjusted to their current load and become more difficult to trigger. The most suspect areas to release this avalanche problem would be trigger points and areas where the snowpack thins to a below-average depth. Such as near rock bands, on some slopes that previously avalanched and have refilled, or where winds have formed variable snow depths. Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes. You can reduce your risk by traveling on slopes with a deep, uniform snowpack, and you can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees and not connected to steeper terrain above.  

     

     

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full-width last week.  This avalanche would be hard to survive.

Avalanche Discussion

Snow totals exceed a foot of settled storm snow in the Northwest Mountains and up to 10 inches in the Southeast Mountains.  In the Northwest Mountains, the avalanche danger is largely driven by the new snow accumulations.  Reports from yesterday afternoon, near Irwin, indicated sensitive Storm Slab avalanche conditions in 10 inches of storm snow.  Snowfall continued to accumulate last night and now Storm Slabs are over a foot thick in sheltered areas and a bit deeper where the wind has drifted snow onto leeward slopes.  Additionally, observations of Surface Hoar formation from this past weekend raise suspicions about new snow bonding to the old surfaces (ob 1, ob2).  Carefully investigate the storm snow before you consider entering terrain near or steeper than 35 degrees.  Drifting snow or cracking in storm snow are clear indications of unstable conditions in surface snow.

In the Southeast Mountains, the danger is driven by the chance of triggering an avalanche deeper in the snowpack well beneath the recent storm snow.  In locations where you find or anticipate finding, less than about 5 feet of depth there is an increased chance of triggering a deeper avalanche.  The new load may make triggering a deeper avalanche more likely due to the increased burden.  If you are uncertain about depths or the chance of triggering an avalanche on a deep weak layer, then defer to conservative low-angle terrain to greatly reduce your risk.  Avalanches in the storm snow are still possible in the Southeast Mountains where you find storm totals nearing a foot and on drifted terrain features.

Snowfall continues for the next three days.  As snowfall stacks up the avalanche hazard will slowly increase with the new loads.  Stay tuned in the coming days to follow the changing conditions.

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