Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

New snow and violent winds are creating dangerous avalanche conditions on wind-loaded slopes.  In leeward terrain, natural and triggered avalanches involving today's drifted snow will be common.  Carefully assess the snowpack before riding in steep, wind-protected terrain.  There is isolated potential for an avalanche to break several feet below today's storm snow on buried weak layers.  

Problemi valanghivi

  • Wind Slabs

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

    Strong southwest winds are drifting the new snow into sensitive slabs at all elevations.  They'll be largest and most widespread near and above treeline.  Avoid steep terrain where you find more than about 10" of dense, drifted snow.  Wind slabs will be most common below leeward ridgelines, in gullies, and behind rollovers, although they may form in unusual locations today.  Cracking underfoot or blowing snow signals potential danger. 

    Example of a triggered wind slab from last week's windy storm.  

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–2.5

    There are several layers of small-grained facets in the upper few feet of the snowpack that will be getting stressed by this storm.  We have yet to observe any avalanches breaking on these layers in the Northwest Mountains, but we recommend assessing the snowpack and giving yourself a wider margin for surprises today given the significant loading.  The layers appear to be most problematic on easterly or westerly facing slopes where they are associated with crusts, or in unusually shallow or rocky areas on northerly aspects.  Stability tests can be helpful for identifying this problem, or you can choose more conservative terrain when in doubt.  

    2/27: A stability test in the Anthracite Range that failed on a faceted weak layer a couple feet deep.  

Avalanche Discussion

The first in a series of storms is slamming into the Elks this morning and the avalanche danger will rise through the day and into tomorrow.  Today's issues are most commonly driven by intense wind loading. Wind speeds nearly passed the 100mph mark this morning on Scarp Ridge, and they are certainly mixing into all elevations today drifting the new and recent snow.  Expect easily triggered and natural wind slabs today to be larger and more widespread as you gain elevation. 

Unfortunately, today's travel advice isn't as simple as "avoid wind loaded slopes".  Persistent weak layers in the upper and lower snowpack have been getting stressed during the active weather in the past few weeks.  The persistent slab problem has recently produced avalanches and obvious signs of instability on both wind-loaded and wind-protected terrain of the Southeast Mountains. One layer of concern is a layer of facets or faceted crusts up to a few feet deep, which has produced collapses and avalanche activity on Mount Emmons (Example A, Example B).  We have yet to observe collapses or avalanches on these layers in the deeper snowpack of the Northwest Mountains.  However, we have found a few concerning pit results in recent weeks, such as this propagating test yesterday in the Anthracite Range.  Given the significant loading this week, we recommend carefully assessing the snowpack and/or choosing more conservative terrain to manage for potential surprises of avalanches breaking deeper than expected, similar to this close call during last week's storm.  In the shallower parts of the Southeast Mountains, there is also the isolated threat of avalanches breaking on weak layers near the ground, exemplified by this unstable test result near Mt. Whetstone.  

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