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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In sintesi

A new generation of persistent slabs were formed by the snow that accumulated last week. Many avalanches large enough to bury a person were observed yesterday. These avalanches are most reactive at near and above treeline elevations and more isolated in distribution at below treeline elevations. You can reduce your chance of triggering this avalanche problem by decreasing slope angles and riding in lower-elevation wind-sheltered terrain. Additionally, as the snow surface warms this afternoon, keep an eye out for wet loose avalanches on steep, sunbaked slopes. 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    As the sun warms the snow surface, wet loose avalanche activity will become possible. This potintal avalanche problem will first develop on steep slopes, that have rock outcrops adding additional heat to the surounding snow. A few inches of wet snow and fresh roller balls are early warning signs that this avalanche problem is developing. If this avalanche problem develops in your area, consider moving to lower-consequence terrain or a colder aspect. 

    A wet loose avalanche that released below cliffs during the last warmup. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    2 to 4 feet of new snow has accumulated since March 3rd. That snow is settling into a slab over a variable distribution of small facets, surface hoar, and collapsible crusts. This new persistent slab avalanche problem is the most reactive on previously wind-loaded terrain. The avalanche problem becomes more spotty in distribution on lower-elevation wind-sheltered slopes. Previous wind-loading patterns are not observable as they are often covered by low-density snow that fell after Thursday's extreme wind event. Consider evaluating the slab characteristics over these persistent weak layers in your area, or more simply, manage the potential avalanche problem through your terrain choices. Such as choosing lower-angled slopes and/or avoiding high-consequence terrain features. 

    There is also a low probability that an avalanche could release at the middle or bottom of the snowpack and become very large in size. The most suspect areas to trigger one of these suprize avalanches would be where there are many trigger points and a variable snowpack depth, such as a steep rocky face. 

    This was the largest pair of persistent slab avalanches observed on Friday and the type of avalanche you don't want to become involved with. 

Avalanche Discussion

Winter returned to the forecast area this week after a period of unseasonably warm temperatures. The first winter storm on March 3rd-4th delivered up to two feet of snow in the Ruby Range, with significantly lesser amounts in the Southeast Mountains. The second winter storm arrived on the evening of March 5th and delivered 9" to 20" of snow by the morning of March 7th, along with Strong to extreme Southwest winds. We are now moving under a high-pressure ridge, and there is a rising temperature trend over the weekend. You can read the full weekly summary here. 

We haven't yet observed any avalanches breaking near the bottom of the snowpack. This may be in part due to Thursday's storm not delivering the full loading event that was initially forecasted. With that, the deep slab avalanche problem was removed in the NW Mountains, and now both forecast areas are covered with the same persistent slab avalanche problem that is highlighting this new generation of slabs. South and southeast aspects were added to the problem distribution rose after this surprising avalanche was observed on Mt Baldy. 

The most avalanche activity observed so far has been in the NW Mountains forecast area, with less activity reported in the SE Mountains. However, this imbalance may change as we gain better visibility into the SE Mountains. Additionally, the snowfall in the SE Mountains may not have been sufficient to form new slabs, except in areas affected by wind loading. These mountains also contain more pronounced weak layers in the middle and lower portions of the snowpack. Further assessment is needed to determine whether the recent loading has made these layers more reactive. It will be interesting to see how avalanche distribution and activity evolve in the coming days.

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