Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Signs of instability abound liking cracking, collapsing, and recent avalanches.  The loading period has largely ended but some drifting was observed yesterday at the highest elevations and weather stations this morning suggest that winds are strong enough to transport snow at upper elevations.  You are likely to trigger an avalanche in the storm snow or on deeper weak layers today.  Direct feedback from the snowpack might begin to decrease in the Northwest Mountains, but do not allow this to lull you to sleep.   Take the time to choose a route plan for your day that avoids steep terrain at upper elevations and problematic aspects.  Consider the possibility of remotely triggering an avalanche on steep terrain from below or adjacent slopes.  Place a healthy margin between your group and suspect terrain features.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Persistent slabs remain ripe for human triggering after Monday night's heavy snowfall.  On or near steep terrain, you can easily trigger slabs 3 to 5 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.   Choose routes that stay off of, and out from underneath, steep terrain holding slab over weak layer structures, which are most common on the slopes highlighted by the distribution rose above.  Shooting cracks, collapses, and recent natural activity are all glaring red flags to stay on slope angles less than about 30 degrees.   

    12/29: A remotely triggered persistent slab below treeline. The crown was almost 3 feet thick.

  • Storm Slabs

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

    Monday night's storm spurred a storm slab cycle in the new snow.  Although new snow instabilities will be quicker to heal than persistent slabs, slabs of new and drifted snow remain a secondary concern today.  You are most likely to find this instability on steep terrain at higher elevations where slabs are thicker and stiffer from wind effects.  Shooting cracks, like this observation, are clear warning signs.    Look for feedback on small test slopes before considering more consequential terrain.  Storm slabs are entraining enough snow to be dangerous by themselves, but they can also step down and trigger larger persistent slabs on problematic aspects.    

    12/29: A large storm slab that released from a wind drifted ridgeline on Schuylkill Ridge.

Avalanche Discussion

What's that? oh, you like pictures of avalanches. Well, here you go...yesterday's clear skies provided for avalanche viewing around the forecast area and there is no shortage of recent activity from all elevation bands.  Take a look through the pile of observations from yesterday to see the tower of evidence that the snowpack is going to need more time to adjust to the new burden.  The majority of the avalanches ran early on the morning of the 29th at the tail end of the storm, but some failed later including yesterday (ob1, ob2).

For today, the terrain of the greatest concern will be recently drifted terrain features at upper elevations closely followed by sheltered terrain on aspects highlighted by the Persistent Slab rose that hasn't already avalanched.  Triggered avalanches in these areas are likely to be large in size and will not be forgiving to a mistake.  The Northwest mountains developed slaps over the widespread weak layer over two weeks ago, but the Southeast Mountains, including Brush and Cement Creeks, were lagging behind in dangerous slab formation below treeline until Monday's storm deposited an additional foot of snow.  Expect below treeline slopes in the shallower-snowpack areas of the CBAC forecast zones to now have slabs that are sensitive to human-triggering.  Conservative decision making and terrain choices are your best defense against unpredictable Persistent Slab behavior.  Rumbling collapses are a clear sign that remotely triggered avalanches are a genuine concern.  Make sure that you closely manage your group's spacing and position in and around avalanche terrain to prevent being surprised by wider-than-expected propagation.  Keep your guard up even around small terrain features like cut banks, steep creek bottoms, or clearings in the forest.

Your secondary concern is with the storm snow itself.  The recent snow ranges from 8" to 18"  deep in sheltered areas which is enough to cause harm.  If you are traveling on steep terrain with 10" or more of storm snow you should make a thoughtful snowpack assessment prior to committing to avalanches terrain regardless of aspect.  Observations suggest the bonding between the new storm snow and old surfaces is poor.  On sunny slopes, the storm snow is resting on slick crusts, and on shaded slopes a mix of small near-surface facets and even surface hoar in some protected places. 

Regions covered