Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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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 this past week, we have seen multiple days of accumulating snow and strong southwesterly winds further loading that snow onto the lee sides of terrain features. Today, the most dangerous areas remain on these previously wind-loaded terrain features. In wind-sheltered areas, there is a notably lower chance of triggering a slab avalanche. Later this afternoon when temperatures climb to near or above freezing, avalanche problems may briefly become more reactive. Such as this observation a week ago, when a small wet loose avalanche pried out a bigger wind slab avalanche. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    Since the last Wednesday over two feet have fallen in the Northwest Mountains. That snow was accompanied by continued strong winds with periods of extreme winds. The wind direction aloft was primarily from the Southwest, but with some variation. Dangerous avalanche conditions remain on these previously wind-loaded slopes and they need more time to adjust to this loading event. Previous wind loading will most commonly be found at near and above treeline elevations, below ridgelines, and on cross-loaded terrain features, while you can further find a few outliers in open areas at below treeline elevations. 

     

    An example of a wind slab hanging out below a ridgeline. 

  • Persistent Slabs

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

    Since the end of January, the upper snowpack has become layered and more complicated. After this past week's loading event, we can't yet completely rule out slab avalanches releasing 1 to 2 feet deep on the old snow interface, or several feet deep on buried weak layers in the upper half of the snowpack. The highlighted areas above are essentially shoulder aspects where crusts become thin and faceted as they taper from south to north-facing slopes. These may not be the only places where this low-probability avalanche problem exists, but they are the most suspect.

    Don't expect to see any obvious signs of instability or early warning signs for this avalanche problem. So consider the potential avalanche size when making your terrain choices and picking regrouping areas. 

    An example of buried layers of facets sandwiched between thin crusts.

Avalanche Discussion

Today will no doubt be an excellent day to get out and ride the backcountry. There is some superb skiing and riding in wind-sheltered terrain, with nice weather in today's forecast. Just don't forget about the recent weather events that we just went through. The wind has been responsible for some significant loading during the last week. The avalanche problems in that terrain are probably already becoming stubborn to human triggering, however, a triggered avalanche could easily break above you and become larger and wider than expected. 

In more wind-sheltered terrain, the storm slab avalanche problem is fading away. There are isolated areas where we can't completely rule out a slab avalanche releasing on the old snow interface. Small pockets in extreme terrain, where those slabs have little support above cliffs or steep rollers, would be one example of these isolated areas. As temperatures climb to near or above freezing this afternoon, we could see a brief window where avalanche problems become more reactive.

The persistent slab avalanche problem is the most widespread in the SE Mountains. This observation from Mt Emmons highlights deep cracks in the snowpack after a skier descended into the slope. The SE Mountains have also seen large persistent slab avalanches release on wind-loaded terrain several times this month during and after wind-loading events like we just had. In the Northwest Mountains, we have not yet observed avalanches breaking into weak layers buried in the upper half of the snowpack, but we are highlighting that there is a low probability of this occurring. Forecasters have been keeping track of potential weak layers that were buried earlier this month and have noted that the potential exists.  

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