Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

We are finishing a long week of continued dangerous avalanche conditions with little change in the coming outlook. Be careful not to let message fatigue set in or allow complacency to develop. Daily observations continue to report both avalanche activity and obvious signs of instability. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5

    Recent snow accumulations have provided fuel for fresh wind slabs to form. For the most part, this avalanche problem is stacked on top of the larger persistent slab avalanche problem and the latter here should be dictating your terrain management. However, in a few situations, it will be important to understand that recent southwest winds have been strong enough to transport snow, building fresh slabs, and loading lee terrain features. 

  • Persistent Slabs

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

    A widespread weak layer was buried by a potent storm earlier this week and produced a notable avalanche cycle. Friday's storm further overburdened the same weak layer while producing more human and natural avalanche activity. You can expect typical Persistent Slab behavior like wide propagation and remote-triggering of slopes from below or adjacent terrain. 

    This avalanche problem is the largest in size on the lee sides of wind-loaded terrain features. While the problem will be most sensitive to human triggering on the northern half of the compass. On southerly-facing slopes, the weak layer distribution is not as widespread. On some southerly-facing slopes, you may find those same slabs sitting on facets/crusts and creating dangerous avalanche conditions. While in other areas the weak layer may not be continuous across the terrain, or if the slope didn't hold old snow prior to the last storm, there will be an absence of the problematic weak layers.

    A widely-propagating avalanche failed during Tuesday's natural cycle.  Friday's storm will produce another round of avalanches like this.

Avalanche Discussion

A member of the forecast team was out walking their dog yesterday and was able to trigger a slab avalanche. In the avalanche forecasting world, that's a layup and it sure doesn't get much easier than that. Over the last week, we have seen two HIGH danger events, one observed natural avalanche cycle, many human-triggered avalanches, and an overall continuation of the dangerous avalanche conditions. If we want the avalanche danger to decrease then we need it to stop snowing and I don't think any of us are ready for that. 

Another interesting observation is about the confidence in the forecast community as a whole right now. We've recently come out of forecasted HIGH avalanche danger and haven't had much visibility to verify how things played out. Some slopes have avalanched earlier this week, in some cases flushing the weak layer, while in others the weak layer will not have been cleaned out. Those avalanche paths have since been refilling with more snow. Other avalanche paths have not released and are just barely hanging in the balance. The last generalization is that in some other areas we don't have any weak layers and are just slowly building a stable snowpack. The line between these scenarios has become blurry, and it will be easy to walk over that line without knowing it. 

Yesterday we picked up about 2 to 5 inches of snow depending on the area. Winds have generally been light, but up in the alpine, they have certainly been strong enough to transport snow. For example, yesterday the Scarps Ridge weather station was recording an average wind speed in the 20's and gusts of around 40mph. The CBMR wind station also recorded an average wind speed of around 20mph and gusts of around 30mph. Those southwest winds will have continued loading the persistent slab avalanche problem and building fresh wind slabs on the lee sides of terrain features. 

If you are out trying to satisfy that built-up powder fever, here are 4 key categories to focus on when deciding where to head for the day. Aspect, overhead hazard, slope angle, and consequence if you were to get it wrong. 

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