Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

An AVALANCHE WARNING is in effect for the Northwest Mountains.  The danger will rise to High later today and tonight as heavy snowfall rates and windloading overload a teetering snowpack.   Large avalanches are likely to fail naturally, and you can easily trigger a dangerous avalanche while on or below steep terrain.   Mind your overhead hazards.  Travel in avalanche terrain is not recommended.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–2.5

    Heavy snowfall and windloading will make persistent slabs very easy to trigger today, and they are likely to fail naturally.  There's a widespread weak layer of facets and faceted crusts buried by 2 to 4 feet of recent snow on west to north to southeast aspects. The slabs are largest in leeward terrain at higher elevations.  The problem is less common, but still possible, on windward terrain or south facing slopes that hold old snow layers near the ground.  Choose routes that keep you off and out from under steep terrain that holds old snow below our recent storms.  Collapses and shooting cracks are clear signs of danger warning you to stay on slope angles that are consistently less than 30 degrees.  

    Several recent persistent slab avalanches on Schuylkill Ridge

  • Storm Slabs

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

    Heavy snowfall rates and moderate to strong winds today will quickly form shallow storm slabs.  Today's snow is accumulating on a widespread layer of graupel that fell yesterday, which could cause these slabs to be unusually reactive.  Storm slabs will be larger on higher elevation, leeward terrain.    Relatively shallow releases in the storm snow are likely to step down and trigger a larger persistent slab avalanche where the two problems overlap.  

    12/5: This weak layer of graupel is widespread on the snow surface and getting buried by new and drifted snow today.

Avalanche Discussion

24-hour storm totals range from a couple of inches near town to 8" at Upper Taylor and .5" SWE at Schofield Pass.  Winds have been blowing 25-35 mph and gusting to 60 mph on Scarp Ridge.  The heaviest period of snowfall is expected to arrive today, with up to a foot of snow favoring the Northwest Mountains.  See our weather tab for details.  

Just like our last two storms, natural avalanche activity is expected to resume throughout the day as heavy snowfall rates and wind loading overburden our fragile weak layers.  The danger is highest near and above treeline in the Northwest Mountains, where the most intense loading is occurring and destructive sizes are largest.  The distribution of persistent slab avalanche activity today is expected to follow similar patterns as our last two cycles, while destructive sizes continue to creep up with larger and stiffer slabs.  I've kept the persistent slab size slider maxing out at D2.5, but I won't be surprised to see a few outlier D3s run from the largest alpine start zones of the Northwest Mountains.  

The snowpack isn't nearly as dangerous on slopes that were bare dirt prior to our recent storms.  These two observations from the Northwest Mountains and Southeast Mountains document the distribution of our problematic weak layer that formed during November's dry spell.  In terrain that's lacking old snow, you'll need to manage for shallow storm slabs and wind slabs that are forming over a widespread layer of graupel that fell yesterday.  

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