Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Avalanche conditions incrementally improve as the snowpack adjusts to the loading event on Tuesday.  There is a threat of triggered avalanches on drifted terrain with the most concerning places being shallower than average due to previous avalanche activity, previous wind effects, or rocky terrain.  Similar concerns exist for sheltered terrain on the north half of the compass where slabs several feet thick rest above weak layers from early February.  Evaluate the terrain and avoid locations that you suspect have variations in slab thickness and an increased chance of finding a trigger point.  If you were to impact a weak layer expect to trigger a large and dangerous avalanche.  If you choose to step into avalanche terrain you can reduce your risk by selecting smaller slopes with clean runouts.  You can find lower-risk options on wind-sheltered, southerly terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Heavy snowfall and intense wind loading Tuesday added significant amounts of stress to weak layers in the snowpack, causing large and dangerous natural avalanches.  The threat of avalanches breaking on old weak layers will slowly decline as the snowpack adjusts to the loading event earlier this week.  The most prominent and active weak layer is buried surface hoar several feet deep on the north half of the compass. There is also potential for avalanches to break on faceted crust layers on some higher, southerly aspects, or depth hoar layers near the ground.  Persistent slab avalanches can be remotely triggered from low-angle terrain and break larger and wider than you might expect.  Low-elevation southerly aspects are significantly less problematic, and slope angles consistently less than 30 degrees are a reliable way to avoid the problem.  

    A broad avalanche on the north side of Crystal Peak that ran during last week's storm.  

  • Wind Slabs

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

    Intense wind drifting on Tuesday formed slabs of varying thickness on wind-loaded terrain features at all elevations.  Tuesday's winds shifted from southwest to northwest, so you will most likely find slabs on the east half of the compass or cross-drifted features elsewhere.   Use visual clues to identify where drifting snow landed: it will look and feel deeper, stiffer, and more rounded.  Some of these slabs will be hard and stubborn already, others are easy to trigger.  You can avoid the problem and find softer, higher-quality snow in wind-sheltered terrain.  Consider slab size and terrain consequences before crossing a drifted slope. On steep slopes where fresh wind loading overlaps with larger persistent slab issues; triggered slabs in the upper snowpack can step down and produce much larger avalanches. 

Avalanche Discussion

Avalanche hazards slowly improve with time since Tuesday's loading event as the snowpack gradually adjusts to the new burden.  Dangerous human-triggered avalanches remain a threat in both forecast zones but you will find worse conditions in the Southeast Mountains as slabs are thinner overall creating 'easier-to-trigger' avalanches.  A good example of this can be seen in the natural avalanche on Gibson Ridge that was visible a first light yesterday. 

In the Southeast Mountains, weak layers in the upper snowpack commonly reside at a depth of 1.5 to 3 feet; this is a prime depth for human-triggered avalanches.  Observations from around Snodgrass found moderate propagating test results in multiple locations with slabs around 2 feet thick above the early February weak layer.  When you couple the test results with the natural avalanche on Gibson Ridge and the overall poor-looking structure, it's not hard to imagine triggered avalanches in sheltered terrain harboring surface hoar several feet deep.  In wind-drifted areas, the threat of avalanches breaking deeper in the snowpack should remain on your mind.  A fresh avalanche from the Aspen area yesterday highlights the increased potential for deep failing avalanches in shallower snowpack areas in the region.

The Northwest Mountains, have thicker slabs in general above the early February weak layer and basal depth hoar.  This results in a reduced threat of triggered avalanches however it remains possible for you to impact weak layers and release a dangerous avalanche.  You are more likely to impact weak layers where slabs become thinner.  This could be due to previous avalanche activity, previous wind erosion, or rocky, uneven terrain.  A good example comes from the recent destructive avalanches on Axtel (Green Lake Bowl, 4th Bowl) on Tuesday; extensive recent drifting on slopes with shallower snowpack depths due to previous avalanche activity and wind erosion is the likely scenario on Axtel.  You can find safer options in wind-sheltered areas, but here too there may be landmines hidden beneath the snowpack creating invisible trigger points around buried rocks or convex rolls.  Even though triggered avalanches are less likely in the Northwest Mountains, if you were to release an avalanche it is likely to be large and dangerous.

Wind-sheltered sunny slopes have the least worrisome snowpack.  Warming conditions today and sunshine may make for soft surfaces and pleasant riding conditions.  Steering away from problematic wind-loading and buried persistent weak layers is one way to reduce your risk.  Keep an eye out for previous drifts at low elevations from Tuesday's wind event and monitor surface warming in case lower elevation sunny slopes warm more than expected. 

You can always use low-angled terrain to manage avalanche risks and enjoy great snow on shaded aspects.

Events: The CBAC Fireside Chat Series presents legendary American alpine climber George Lowe on Sunday, March 3 at the Mallardi Cabaret Theatre in downtown Crested Butte at 6 p.m. Best of all, it’s free!

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