Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Storm totals since Friday night are approaching 30" in the Northwest Mountains.  Continued snowfall and a potential increase in winds later today keep the threat of natural and human-triggered avalanches going.  Use extra caution on shadier aspects and in drifted terrain.  Avalanches can break in the storm snow, especially where winds are stiffening the snow.   On slopes with a northerly tilt, dangerously large avalanches can fail several feet deep on the problematic weak layer that continues to produce warning signs such as rumbling collapses.    Cracking, collapses, blowing snow, or recent avalanche activity are all warning signs.  Southerly facing terrain protected from the wind offers the easiest snowpack to manage right now. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    On the northern half of the compass, you can trigger a dangerous slab avalanche that breaks 3 to 5 feet thick on weak faceted snow buried last month.  Slabs can be triggered remotely from below or adjacent slopes.  Collapsing and cracking are clear signs that steeper slopes are primed to avalanche, although feedback on this problem is variable because of a narrower distribution and as slabs get thicker and harder to trigger.  Conservative terrain selection will help you manage persistent slabs on west to north to east aspects.  

    This photo from Cement Creek illustrates how persistent slabs can be triggered from a long ways away from the start zone.  The avalanche was remotely triggered by a snowmobile on 2/27.

  • Storm Slabs

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

    Soft slabs breaking in the storm snow will become easy to trigger if winds and/or snowfall rates increase today.  Slabs will be most common in wind drifted terrain or in areas that receive heavy convective snow showers.  Use small test slopes to get feedback on how the problem is behaving before committing to steep terrain.  Use extra caution below leeward terrain features at higher elevations.  A smaller avalanche in the storm snow could step down and trigger a larger, denser persistent slab where the problems overlap.  

    An example of an avalanche breaking at the bottom of storm snow below treeline on a steep convexity.  

Avalanche Discussion

Another snow squall last night brought 3" to 4" of low-density snow.  Convective snow showers later today will bring another round of hit-or-miss snowfall favoring the Northwest Mountains with up to 6" or so.  Winds have increased a few notches since yesterday, and we may see a further uptick in winds as this system exits later today.  There is plenty of low-density snow at the snow surface, so a sudden change in winds, or a quick hit of heavy snowfall, can quickly flip stability at the snow surface.  On any aspect or elevation today, plan to manage for storm instabilities.  These could present as loose dry avalanches or soft slabs, depending on how much wind affects you find.  

The more challenging problem to manage is the lurking persistent weak layer buried several feet deep on the northern half of the compass.  Warm temperatures and meltwater last week reduced the threat of this problem on southerly aspects, so those are the aspects I would head to first if I was looking to work into steeper terrain.  We continue to get feedback from the persistent slab problem, such as rumbling collapses.    The problem is becoming more stubborn in the Northwest Mountains, where it is buried deeper and has gained more strength in the past few weeks. However, the potential size is also larger in the deeper areas.  The distribution of the problem isn't nearly as widespread as it was during our last cycle in late February, which means feedback is variable and instabilities are hit or miss.   We also have concerns about faceted bedsurfaces from the last cycle refilling and becoming unstable again.  So far, we haven't seen evidence of this becoming an issue yet as slabs are just starting to rebuild (See this observation).  In the most snow-favored areas, those scales could be tipping with today's additional snow.  

Regions covered