Avalanche forecast

Southeast Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Storm totals will near or surpass 6 inches for portions of the Southeast Mountains and moderate northwesterly winds have drifted the new snow to leeward terrain features.  Slopes with frozen and supportive crusts below the recent storm should prompt you to manage instabilities in the storm snow.  At lower elevations, where the storm snow may rest on a wet, mushy snowpack you should continue to manage for wet avalanche problems.  Look for and avoid terrain with signs of fresh drifting at upper elevations and if you find a wet, unsupportive snowpack below treeline, defer to lower angled terrain.

Avalanche problems

  • Wind Slabs

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

    Storm totals range from about 5 to 9 inches at upper elevations in both forecast zones with a chance of a few more inches today.  An uptick in westerly winds yesterday and a forecasted bump in northwest winds speeds today will transport the new snow to leeward terrain features at upper elevations.  Look for smooth, rounded pillows of snow beneath cornices, below ridgetops, and cross-loaded into gullies or behind breaks in the terrain.  Cracking is a clear sign of instability in the storm snow.  Terrain in the Ruby Range (Northwest Mountains) accumulated the most storm snow so expect larger and thicker slabs as compared to the Southeast Mountains.  

    An example of a small Wind Slab from two weeks ago.  Avalanche size may be larger than pictured here, particularly for the Northwest Mountains.  Expect to find fresh drifts hiding behind terrain breaks like those pictured here.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Tuesday delivered cooler temperatures with near and above treeline locations remaining below freezing for more than 24 hours which has greatly reduced the threat of Wet Slab/Wet Loose avalanches at upper elevations.  Below treeline the temperatures were milder leaving Wet Slab/Wet Loose avalanche concerns to lower elevations.  An observation from Tuesday showed a good amount of liquid water lingering in the February facet layer on northeast terrain below treeline which maintains suspicions for Wet Slabs on shady low elevation terrain.  The most concerning terrain face northwest to north to northeast at lower elevations but you may find wet mushy snow on all aspects which could present a loose avalanche concern.

    3/27:  This destructive wet avalanche on Gothic Peak started as a wet loose and then propagated as a narrow wet slab as it ran further downslope.  

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    On the northerly aspects, there is a rare but dangerous chance you can trigger a hard slab avalanche that breaks up to several feet thick on weak faceted snow that was buried last month.  The new snow will add burden to buried weak layers and cause a slight uptick in the likelihood of you triggering a large slab avalanche. Slabs can be triggered remotely, from below or on adjacent slopes.  Given the thickness and hardness of slabs, you are unlikely to get direct feedback, such as collapsing or cracking, until it's too late.  In the Southeast Mountains, slopes holding a snowpack deeper than 1 meter and less than 2.5 meters are most suspect.   When in doubt, head for lower consequence terrain or slope angles in the lower 30-degree range and less. 

    This large persistent slab avalanche was remotely triggered on 3/18. 

Avalanche Discussion

There are two key weather details to discuss; the first is the cooler temperatures and the second is storm totals.  The terrain above 11,000 feet has been below freezing for more than a day which has greatly reduced the threat of wet avalanches at upper elevations.  Below 11,000 feet, last night's freeze was an improvement from recent nights, but temperatures hovered in the upper 20's for around 8 to 10 hours.  The marginal freeze below treeline has kept wet avalanche concerns alive for today.  On low elevation northerly slopes, meltwater continues to drain through the snowpack and potentially destabilize the persistent weak layer that was buried in late February.  Additionally, sunnier slopes may present a mushy unsupportive snowpack that can produce human-triggered loose avalanches which could entrain most of the snowpack.  Take the time to assess the snowpack at low elevations by looking for a supportive crust just below the recent storm snow.  If the snowpack feels punchy and/or unsupportive underfoot then simply choose lower angled terrain to avoid triggering a nasty wet avalanche.  Tonight's weather forecast will provide clear skies and the coldest temperatures in a week and it is expected to greatly reduce the threat of wet avalanches on Thursday below treeline for most of the forecast area.

Storm totals vary greatly across both forecast zones ranging from 5 to 10+ inches at upper elevations.  Yesterday brought a period of moderate to strong west-northwest winds that transported the new snow to leeward terrain features.  Another round of increased northwest winds will occur today transporting even more of the new snow to leeward locations.  Poor visibility yesterday limited observations of drifted terrain, so some uncertainty exists about how sensitive and widespread newly formed drifts will be.  Take the time to look for and assess any drifted terrain before you enter steep slopes.  Fresh drifts will be the largest in the Northwest Mountains as storm totals were greatest there.  Cracking in the storm snow is a clear sign of unstable conditions.

There is a small chance that you could trigger a Persistent Slab avalanche several feet deep on upper elevation northerly slopes.  This problem has been rather quiet lately around Crested Butte and has provided no feedback or signs of instability recently.  The problem is more concerning in the Southeast Mountains as slabs are generally thinner and weak layers are more pronounced.  The problem is unlikely due to reduced distribution from the recent warm weather, and the slowly decreasing sensitivity to human triggers.  Consider the terrain consequences and potential avalanche size if you choose to recreate on high elevation northerly slopes.  

Regions covered