Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

You can trigger soft slab avalanches breaking in the new and recent snow, most commonly near and above treeline.  Numerous human-triggered slides yesterday exemplify the problem, including one close call/ remote trigger near Marble.  Slabs will be the largest and most dangerous on wind loaded slopes at high elevations - the safest riding is at lower elevations where slabs are thinner and more isolated. On high, northerly aspects, there's a rare chance you can trigger a much larger slab in steep terrain where snow depths are thin and variable.

Avalanche problems

  • Storm Slabs

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

    New and windblown snow this week has formed slabs 1 to 2 feet thick, especially on terrain features favored by westerly winds.  These slabs formed over various surfaces, including slower-to-heal facets on some slopes.  Carefully assess slab size and terrain consequences before riding in steep terrain. Expect spatial variability in how slabs are bonding; use small steep slopes to gather stability feedback.  Cracking or collapsing are obvious signs of unstable snow.  The problem is smaller and less common at lower elevations.     

    A skier triggered storm slab yesterday near Cascade Peak. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–2.5

    The snowpack remains winter-like on high, northerly aspects, and faceted weak layers linger near the bottom of the snowpack.   Persistent and deep persistent slabs are most likely triggered by cornice falls, or there's a slight chance you can trigger one from a shallow or rocky part of a steep slope.   Terrain where the snowpack is unusually shallow from wind effects or previous avalanche activity is most concerning.  You can reduce your risk by traveling where the snowpack is deep and uniform, and you can avoid the problem on sunnier aspects that have a spring-like snowpack that saw extensive meltwater last week.

    A recent persistent slab above Peeler Lakes. This is a great example of the most worrisome terrain: thin, rocky, and wind-affected.   

Avalanche Discussion

Clearing skies yesterday allowed us to extract some avalanche patterns from Tuesday's storm, which produced up to 20" in the Northwest Mountains and less than 6" in the Southeast Mountains.  Storm instabilities were most active near and above treeline and favored the Northwest Mountains.   A handful of these avalanches were large enough to bury you (D2 in size), and these generally occurred on large, leeward slopes near alpine summits.  Although most storm instabilities are improving, some formed over faceted weak layers and are slower to heal.   These forecaster observations from Baxter Basin and Elkton discuss the spotty distribution and inconsistent pattern of this buried weak layer, which was likely the cause of the remote trigger in Marble yesterday.  We're still calling the problem a storm slab today, but the problem is expected to transition into a new generation of persistent slabs as time goes on. Choosing terrain with smaller consequences can help you manage uncertainty where recent storm totals exceed a foot or more.   The problem is easier to navigate in the Southeast Mountains because slabs are generally smaller and only formed on wind-loaded terrain features.  Another round of fresh wind slabs could form from today's snow and southerly winds. Below treeline, slab instabilities are generally small and isolated, and the avalanche danger is Low this morning.  We're showing Moderate danger in the Northwest Mountains below treeline due to uncertainty with incoming storm totals today; if we reach or exceed the high end of snow forecasts, storm instabilities could become more active.   

A notable exception to the pattern of storm instabilities is this large natural avalanche above Peeler Lakes.  This appears to be a recent hard slab that failed on old weak layers. High northerlies are the only slopes that didn't see extensive meltwater into the snowpack last week. On those colder aspects, a more winter-like snowpack structure exists and requires consideration for the early-season weak layers that have plagued us this winter, especially on terrain with unusually shallow snow depths. The most recent human-triggered examples of the problem include a snowmobile-triggered slide on Axtell and a skier-triggered slide on Gothic.   In the San Juans yesterday, a skier was surprised when they triggered a shallow wind slab that stepped down and produced a very large avalanche. 

Events: CBAC's Party for the People is at the Talk of the Town next Thursday.  Come celebrate the end of the season with us!  (Don't worry, we'll be forecasting for at least a few more weeks.)

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