Bollettino valanghe

Gunnison

Crested Butte Avalanche Center
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Pericolo valanghe

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

In sintesi

Recent westerly winds formed small, drifted slabs on the east half of the compass at upper elevations.  To avoid triggering a small avalanche, you will want to identify smooth, pillowy drifts below ridgelines, behind tree fences, or on inset, gully features and steer around them.   An unlikely,  but not impossible, type of avalanche could fail in old, weak snow at the ground.  To avoid dealing with this slim chance, you can simply avoid avalanche terrain that faces north and northeast at upper elevations. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    At 12,000ft, westerly winds have been gusting into the 30's, while slowly building Wind Slabs on the leeward sides of ridgelines and cross-loaded gullies. These slabs are expected to be generally small in size, up to about 18" thick. These slabs will have the best distribution above treeline, and be significantly more isolated in their distribution at near treeline elevations.

    Observed natural avalanche on a northeast-facing slope near Purple Mountain (11/25). Failed in drifted snow immediately below the ridgeline.

  • Persistent Slabs

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

    A patchy distribution of hard slabs on top of old, sugary snow exists on some high elevation, northerly-facing terrain features.  Although these persistent slabs are difficult to trigger, the resulting avalanche would break near the ground and have the power to drag you over rocks, stumps, or early season obstacles. Be cautious of terrain where you find thick, dense snow overlying a continuous layer of weak, faceted snow on the ground.  Snow depths are shallow enough that probing with a pole can help you track this structure across an area prior to committing to avalanche terrain.

    High northerly aspect? ☑. Smooth ground cover? ☑. Weak snow on the ground? ☑. Windloaded slab? ☑. Here's what it looks like when you've found the ingredients for our current persistent slab problem.

Avalanche Discussion

Westerly winds, yesterday and last night continued to blow hard enough to maintain loading on easterly facing slopes at upper elevations.  Natural avalanches were observed yesterday on drifted features that face the east half of the compass (Here is another observation with more Wind Slab details).  You can expect similar terrain features to offer the possibility of human-triggered avalanches today.  Use your eyes to identify slopes of concern by looking for fresh, rounded drifts of snow in leeward locations.  You can feel the stiffness change in the snow with your poles, feet, or machine.  If you feel or see recent drifting, then you can simply avoid it to help reduce your chances of triggering a small avalanche.  Even though these avalanches remain on the small side, they can still injure you or worse by triggering a deeper avalanche in old snow near the ground on northerly slopes.  There has not been any evidence of avalanches stepping down, but it's a chance that should be on your radar if you are thinking about recreating on drifted alpine terrain that faces north or northeast. 

This observation from a few weeks ago documents some of the terrain that holds old, weak snow near the ground and therefore the terrain that can produce avalanches breaking near the ground.  This problem layer has been relatively quiet thus far.  Finding the right combination of a continuous weak layer and a slab is necessary.  Slopes with smooth ground cover should increase your suspicion.  The simplest and most effective tactic is to take the 'lay-up' and simply avoid avalanche terrain that faces north and northeast at upper elevations.  The slopes that hold the necessary ingredients are not the rule, but more the exception.  People have been covering more terrain the past two days and are spreading out to new features for the first time this year; keep your guard up around drifted, shady terrain at upper elevations.  

Regioni coperte