Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

In the Northwest Mountains, avalanche conditions are generally safe in wind-sheltered terrain.  Watch for shallow instabilities in the new snow, especially on drifted features at higher elevations.   Remain cautious of wind-affected slopes with thin or variable snow depths.  That's where there are lingering concerns for triggering a dangerously large avalanche like this persistent slab on Baldy last Friday.  

Avalanche problems

  • Wind Slabs

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

    5" to 10" of snow has accumulated in the past two days and westerly winds have been strong enough to drift the snow into shallow slabs at higher elevations.  Look for cracking underfoot or blowing snow to identify signs of instability.  Wind slabs will be most common below corniced ridgelines or in crossloaded gullies above treeline.  Fresh drifts will be most dangerous above terrain traps like cliffs, trees, or gullies. Seek out wind-protected terrain to avoid the problem.  

    A couple of small wind slabs that ran naturally yesterday on Gothic Mtn.  

  • Persistent Slabs

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

    In the Northwest Mountains, high consequence slabs breaking on older weak layers have become isolated and difficult to trigger.  Persistent slabs are most likely to be triggered from a shallow, wind-affected slope or from random cornice falls. Persistent slab avalanches can be remotely triggered from low-angle terrain and break deeper and wider than you might expect.  The most problematic structures are on shallower slopes on the north half of the compass and a few high, southerly aspects.  Mid to low-elevation, southerly aspects have the most trustworthy snowpack.  Slope angles consistently less than 30 degrees are a reliable way to avoid the problem when in doubt.  

    The crown of a very large persistent slab remotely triggered by snowmobiles on March 8.  This slope is west facing and eroded by seasonal winds, making for a shallower and more problematic snowpack than other slopes. 

Avalanche Discussion

The danger continues to slowly creep up today with another 2" to 5" of snow overnight (up to .5" of SWE) and a few more inches of new snow expected today.   Gradual snowfall over the past two days and light to moderate winds aren't creating significant storm instabilities, but there's been enough drifting snow to form some shallow wind slabs at higher elevations, exemplified by this observation on Gothic Mountain yesterday.   Monitor storm totals, wind drifting, and terrain consequences to manage new snow issues today.  

Snowfall over the past two days is gradually adding small amounts of stress to our persistent slab problem.  The pattern of triggered and natural persistent slab avalanches over the past 2 weeks clearly points to areas with shallower snowpacks being the most problematic.  Most of the avalanche activity has been in the shallower part of our forecast area (the Southeast Mountains), and the few persistent slabs in the deeper zone occurred on windward slopes or on slopes that have repeatedly avalanched this season keeping the snow depth unusually shallow.  It's an appropriate time to step out if you are choosing slopes with consistently deep snowpacks (>200cm), or choosing southerly aspects with strong crusts near the snow surface.  This video of a recent persistent slab on Gothic shows how shallow spots and variable snow depths are more common in wind-affected, alpine terrain.   

Some weather models are calling for significant snow totals tonight accompanied by increasing easterly winds tomorrow.  Winds from the east loading onto our traditionally shallow and windward aspects is a notable change to pay attention to, especially if we see significant snow available for transport.  Stay tuned tomorrow, there's a fair amount of uncertainty about how the storm plays out tonight.  

CBAC Event:  Don't forget the 50th Al Johnson Race is this Sunday, March 17th.  Registration and information can be found at cbavalanchecenter.org.  All proceeds to benefit the CBAC.

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