Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

This is a great day for spring skiing and riding on the southern half of the compass, where normal caution is appropriate. On the north half of the compass, heightened avalanche conditions exist due to a low-likelihood but high-consequence persistent slab problem. Choosing areas with a deeper, more uniform snowpack and fewer thin spots will help reduce the chance of triggering one of these old slabs. This recent avalanche on Mt Whetstone is an example of terrain to avoid, with a thick slab transitioning to thin trigger points around its boundaries. 

Avalanche problems

  • Persistent Slabs

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

    Old, hard slabs 2–3+ feet thick linger over buried weak layers but are becoming increasingly stubborn to trigger and less common. Without obvious warning signs, avalanches are most likely triggered where the slab is thinner and easier to impact the weak layer below. The most fragile layers are buried in the middle and lower portions of the snowpack on northerly aspects. Persistent slab avalanches are dangerous in size; they can propagate widely and be remotely triggered from adjacent low-angle terrain.  The most reliable way to manage this problem is to choose conservative slope angles or travel on southerly aspects, where the snowpack structure has become stronger and more spring-like. On northerly aspects, avoid steep terrain with a thin or variable snowpack, such as rocky areas, rollovers, or places where winds have created uneven slab thickness.

    In the Northwest Mountains, our most recent persistent slab activity occurred during the last week of February, including this pair of destructive slabs.  

    Credit: Irwin Guides

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–1.5

    With good overnight freezes, wet avalanche activity is expected to remain isolated until high temperatures at 11,000ft climb higher than we observed earlier this week, generally towards the low to mid-40's at 11,000ft.  Normal caution travel advice will keep you paying attention as the snow surface melts. If you are in steep terrain and find a few inches of wet snow, you could trigger a small wet loose avalanche. Or, if you find conditions where your boots sink deeply into wet snow, you've found an isolated area that could potentially produce a wet slab avalanche. 

    An example of a wet loose avalanche that ran out of steep rocky terrain earlier this week. Photo: Travis Guy

Avalanche Discussion

Spring conditions look to be coasting along nicely into each sunset over the next couple of days. The mountains saw a good overnight freeze heading into Thursday, and we should see another good freeze heading into Friday. At the same time, high temperatures don't look to exceed what we observed earlier this week. So the snowpack isn't seeing any big changes, which will help with more normal spring conditions. The breezy west-to-northwest winds may keep some upper-elevation wind-exposed slopes more frozen. The next two days look the best for spring riding. Colder temperatures and increased cloud cover will begin to shut down spring skiing this weekend. Next week, we are looking at record-high temperatures and potentially no overnight freezes, which will create an unstable snowpack. 

An extreme wind event passed through the mountains on Tuesday night and into Wednesday Morning. During that event, the wind direction was initially out of the west-southwest, before backing to the west and eventually northwest. Those winds, unfortunately, destroyed much of the soft snow on northerly-facing slopes. They also created a few hard wind slabs. One of those small slabs was human-triggered in steep, northerly-facing terrain near Ohio Pass. While more notably, this large persistent slab avalanche on Mt Whetstone may have run during that wind event.

The recent Whetstone avalanche is the first persistent slab avalanche that we have documented in the forecast area, since a small slab was human-triggered on Snodgrass Mountain on March 4th, or other large avalanches occurred in late February. Outside of our forecast area, there were several destructive avalanches that ran above Conundrum Creek during last Friday's storm.   Closer to home, we continue to find the most concerning snowpack structures along the eastern side of the forecast area. Brush and Cement Creek areas, which typically had the weakest layers going into the February storms, now have thinner slabs that remain more susceptible to human triggers and thinner rain crusts in the upper snowpack. Despite the lack of persistent slab avalanche activity in our Northwest Mountain forecast area, land mines do exist across our entire forecast zone. Careful terrain selection remains essential for managing the persistent slab avalanche problem.

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