Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Yesterday, snowmobilers triggered two slab avalanches in the Kebler Pass area, while a 3rd human-triggered avalanche resulted in a seriously injured skier outside of our forecast area near Marble, CO. Obvious signs of persistent slab instability do not exist. You can travel on multiple steep slopes without triggering an avalanche and then suddenly find either the right trigger point or just the right slope, resulting in a large avalanche. Do not let yourself become complacent due to the lack of signs of instability, and remember recent human-triggered avalanches large enough to bury you have occurred. 

The threat of wet avalanches will increase throughout the day as temperatures rise. Most of these avalanches will be small in size, while a few may pry out old slabs and become large in size, similar to this observation from Cascade Mountain yesterday. Consider avoiding steep sunbaked slopes as you find a few inches of wet snow, or observe fresh roller balls and wet loose avalanche activity.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–2.5

    2 to 4 feet of new snow has accumulated since March 3rd. That snow has settled 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 surprise avalanches would be where there are many trigger points and a variable snowpack depth, such as a steep rocky face. 

    A snowmobile triggered slab avalanche in the Kebler Pass area. March 8th. Photo: Care Flight

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    As the sun warms the snow surface, wet loose avalanche activity will become possible. This avalanche problem will first develop on steep slopes that have rock outcrops, adding additional heat to the surrounding snow. In some areas, a small wet loose avalanche could pry out a larger slab avalanche. You will know this avalanche problem develops when you observe a few inches of wet snow or see fresh roller balls and new avalanche activity. Consider avoiding traveling on or under steep sunbaked slopes once this avalanche problem develops in your area. 

    These wet loose avalanches became large in size when they pried out old slabs yesterday on the SE side of Cascade Mountain. 

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. 

All of yesterday's avalanche activity came from the NW Mountain forecast area, with no new observations in the SE Mountain forecast area. This was likely due in part to the mountains to the west and north of Crested Butte having accumulated more snow last week and just the area that more observers were traveling yesterday. 

Most of the observed persistent slab avalanches are breaking on the March 3rd interface, which was the surface of the snowpack before last week's storms. This will likely continue to be the case in the NW Mountain forecast area. However, in the SE Mountain forecast area, persistent slab avalanches are just as likely to break in the middle or at the bottom of the snowpack. This is due to the SE Mountain forecast area having a comparatively shallower snowpack and more pronounced weak layers deeper in the snowpack. You can, of course, find variations in the snowpack structure between the two forecast areas, and the snowpack where the snowmobile-triggered avalanches occurred yesterday may have a better fit with a structure that is more commonly found in the SE Mountain forecast area. Forecasters are planning to visit those avalanches today. 

The snowpack is experiencing a gradual warmup, with surface crusts and roller balls first occurring on Friday, then wet avalanche activity starting on Saturday, and contenting on Sunday. This slower rate of change is good for helping limit the frequency and size of upcoming wet avalanche activity. The wet avalanches that were reported on the SE side of Cascade Mountain yesterday, which further pulled out old slabs,  will hopefully be an example of the outliers. We can expect more avalanche activity like this, but the majority of wet avalanche activity is expected to be on the smaller end of the scale. 

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