Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The odds of triggering a dangerous avalanche continue to decrease due to our quiet weather pattern.   You can still trigger a large avalanche that breaks near the ground today.   The most suspect terrain is on steep, leeward terrain features near and above treeline, where winds have formed larger and more cohesive slabs above weak snow.   Anticipate variable feedback. Some slopes are stable and some are capable of human triggering.  

Problemi valanghivi

  • Persistent Slabs

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

    On or near steep terrain, you can trigger persistent slabs 2 to 4 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.  To avoid this problem,  choose routes that stay off of, and out from underneath, steep terrain holding dense slabs over sugary weak layers.  Poor structure is most common on the slopes highlighted by the distribution rose above, on west to north to east and some southeast slopes.   Shooting cracks and collapses are clear warning signs to stay on slope angles less than about 35 degrees, although their absence isn't a guarantee of safety.   In the Northwest Mountains, slabs are generally thicker and denser: you are most likely to trigger them from shallow points on the slope such as rock bands, pungie trees, or where slabs taper in thickness from wind effects.  

    12/31: A large, remotely triggered persistent slab in Redwell Basin

Avalanche Discussion

The snowpack around Crested Butte continues to show a promising trend, with fewer collapses, more stable pit results, and a sharp decline in avalanche activity since January 6th.   This is because slabs are starting to lose cohesion and weak layers are starting to adjust to their current overlying slabs.   We clearly aren't out of the woods though.  The weak layers of depth hoar and large-grained facets buried in early December have shown a pattern all season of exceptional persistence, well after loading periods have ended.  We are still getting reports of collapses and/or shooting cracks.   Although the danger is decreasing, the tricky part for travelers looking to step out into suspect terrain is identifying which steep slopes have reached equilibrium and which steep slopes still hang in the balance.  For example, yesterday I was touring with the interns on various aspects of Mt. Axtell.  When we were crossing low angle slopes or digging pits, we would all take bets on which slopes would collapse or give us unstable results.   We stomped on quite a few slopes and dug a number of pits that showed an unreactive problem,  but then a handful of other slopes would produce startling collapses or propagating test results.    While approaching the slopes, our ability to accurately guess which would produce stable vs. unstable results was only slightly better than a coin toss.  By digging into the snowpack and testing the structure, our accuracy improved but was far from perfect.  My point is that, on the suspect terrain that we have been highlighting for the past month, you will find variability and inconsistent feedback, and guessing is not a good approach.   Give yourself a wide margin for error with your snowpack assessments and terrain choices.  Default to lower angle terrain or less consequential slopes when in doubt.  

At lower elevations closer to town, the snowpack is decaying faster and persistent slab structures are becoming more isolated each day.  In this below treeline terrain in the Southeast Mountains, you can also trigger shallow loose dry avalanches where the snow is weak and cohesionless.  

Regioni coperte