Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

In sintesi

The combination of a long dry spell paired with an extreme wind event that generally eroded and stiffened the snow surface has made it difficult to trigger an avalanche.  However, if you do find an instability, it has potential to be large and dangerous.  We recommend cautious travel where you find recent or previously windloaded snow onto steep terrain.  A triggered avalanche yesterday on a heavily windloaded terrain feature below treeline highlights the type of terrain where you can still find trouble.  

Problemi valanghivi

  • Persistent Slabs

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

    The odds of triggering a persistent slab continue to decrease.  On steep terrain features with previous windloading, you can trigger persistent slabs 1 to 2 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 steep terrain holding dense slabs over sugary weak layers.   Following last week's damaging wind event, reading the snow texture and avoiding terrain where the snowpack looks deeper and more windloaded can help you avoid the problem.  The most problematic slopes are on northeast, east, and high southeast facing terrain.  You may be able to find isolated exceptions to the distribution rose on crossloaded terrain features on other shady aspects.  

    1/15: A triggered avalanche on a windloaded below treeline slope. While most of the terrain held soft, faceted snow, this feature held the right ingredients: a stiff slab of wind drifted snow over weak facets.

Avalanche Discussion

The past two days of extreme northwest winds caused a fair amount of forecaster uncertainty.  With good visibility yesterday, our forecast teams spread out into both the Northwest and Southeast Mountains and our confidence has increased.  In general, the winds decreased the number of slopes where you can still find trouble.  The alpine was eroded hard: winds stripped the snowpack away on most windward terrain features, and also carved slabs away on a number of leeward terrain features.  Snow surfaces are stiffer now, further decreasing the sensitivity to human triggers.  It seems that the bulk of snow transport was either sublimated into the atmosphere or channeled into valley locations.  Down valley windloading is where we found the most signs of instability yesterday, and where we were able to trigger a widely propagating slab avalanche on a test slope.  This is consistent with a few other natural wind slabs that were triggered by winds channeling snow transport through lower elevations (Example A, Example B).  We have adjusted the distribution rose to reflect the terrain where you are most likely to find the right ingredients of a dense slab over weak layers.  

Slab faceting has been ongoing for several weeks now, making slabs more isolated and less reactive, especially in windsheltered and windward terrain.   You can use visual clues and probe at the snowpack to help you identify where the persistent slab structure exists:  If the snowpack looks deeper from previous or recent windloading, it is more likely to be a problem.  Drifted areas often look smooth and rounded.  If the snow looks and feels shallow or recently eroded by winds, it is generally safe.  Wind scoured terrain looks scalloped and heavily textured.  Be wary of traveling on steep terrain where shallow snow transitions to deeper, thicker slabs: these slab margins can be trigger points.  

For these reasons, the likelihood of triggering an avalanche has decreased to unlikely.  The expected size remains the same: several feet thick and propagating widely at higher elevations.   Because of this, our travel advice is most consistent with MODERATE danger today.   

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