Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

In the Northwest Mountains, Saturday's avalanche conditions have improved to a low likelihood, high consequence situation.   By carefully choosing terrain with deep and uniform snow coverage, you can reduce your risk of triggering a large and dangerous avalanche that breaks on weak layers several feet deep or more.  Wind-protected or eroded southerly-facing terrain generally lacks problematic snow structures.

An Avalanche Watch is in effect: the avalanche danger will rise dramatically on Sunday due to heavy snowfall and strong winds.   

Avalanche problems

  • Persistent Slabs

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

    In the Northwest Mountains, avalanches breaking on deeper weak layers have become stubborn and difficult to trigger.  You are most likely to trigger a persistent slab on slopes with shallow and variable snow depths on colder aspects.  The most prominent and active weak layer is buried surface hoar several feet deep on the north half of the compass. There is also smaller 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.  Lower elevation southerly aspects are generally unproblematic, 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
    1–1.5

    Strong southwest winds today could form small but sensitive wind slabs on a few high-elevation, leeward slopes today.  Look for blowing snow to indicate a new round of wind slabs are forming.  Stay away from fresh drifts in high-consequence terrain.  They'll look and feel stiffer than wind sheltered snow.  

    Example of a small windslab.  

Avalanche Discussion

Wind slabs from Tuesday's storm have generally healed up. Although there's limited snow available for transport for today's increasing winds to work with, expect to find a few fresh wind slabs forming today, most commonly in alpine terrain with productive and crust-free fetches.    Blowing snow will signal changing conditions.  

Our persistent slab problem is dictating today's avalanche danger and travel advice, and is more dangerous in the Southeast Mountains today.  If you explore our persistent slab patterns since our prominent February 2nd weak layer was buried, you'll see that persistent slab activity in the snow belt (the Ruby Range) has been diminishing in the past two weeks, while activity has continued or even ramped up in shallower areas.  The deeper snowpacks are gradually becoming more trustworthy, and there are now options in the Northwest Mountains to step out into more avalanche terrain with much less risk than earlier in February.  Another good way to visualize this is by looking at accumulated snow water equivalent since our surface hoar layer was buried, which ranges from 9" at Lake Irwin, 7" at Schofield Pass, 5" at Gothic, and 3" on Mt. Crested Butte.  All other things being equal, layers that have been buried under larger amounts of stress for longer periods are more resilient and harder to trigger.  But of course, the potential size is larger.    Observers continue to report dangerous avalanche conditions in the Southeast Mountains, here are a few examples:  Yesterday, a skier triggered a large avalanche on Cement Mountain, and Eric reported finding some of the "worst-looking structures I have seen all season" on an adjacent ridge.  This pit from Carbon Peak with a glaring surface hoar stripe looks pretty darn scary.   On Thursday morning, we spotted a fresh persistent slab on Gibson Ridge that might have been remotely triggered by wildlife.   In short, a more cautious and conservative mindset is required if you are traveling in the shallower parts of our forecast area today. In the deeper parts, continue to assess the snowpack and consider terrain consequences on a slope-by-slope basis: that layer is still out there. 

A note on the persistent slab distribution rose: we trimmed back a few wedges (west below treeline, south and southwest above treeline) due to upper snowpack strengthening from recent surface melt, and because these areas haven't been as productive recently. The persistent slab problem is most worrisome on the north half of the compass where the surface hoar lives. However, we have some isolated concerns and uncertainty for faceted crusts on heavily drifted slopes on the sunnier side of the compass.  On southeast-facing terrain, the last round of wind slabs formed over thin, collapsible crusts in some areas, a potentially persistent issue.  

On Sunday, the avalanche danger will rise in both forecast zones with another potent storm forecasted to bring strong winds and heavy snowfall.  An Avalanche Watch is in place. Depending on how the storm evolves, we expect to reach High danger and Warning criteria in one or both forecast zones.  Storm instabilities will develop, and just like the last storm, more avalanches will break on weak layers deeper in the snowpack, some of which could be very large.  Plan on dialing it way back tomorrow.  

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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