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

Very dangerous avalanche conditions exist today due to an exceptionally large snow and windloading event last night.  Natural and human triggered avalanches are likely:  they can break in the new snow or on weak layers near the ground.  Travel in and below avalanche terrain is not recommended.   Avalanche terrain means any slope steeper than 30 degrees and the lower angled slopes below it.  

Avalanche problems

  • Persistent Slabs

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

    Persistent slabs are ripe for human triggering after last night's heavy snowfall.  On or near steep terrain, you can easily trigger slabs 3 to 5 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.  Avalanches that release naturally from today's snow and windloading could run long distances.  Choose routes that stay off of, and out from underneath, steep terrain holding slab over weak layer structures, which are most common on the slopes highlighted by the distribution rose above.  Shooting cracks, collapses, and natural activity are all glaring red flags.  

  • Storm Slabs

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

    Soft slabs breaking in the new snow will be easy to trigger today on steep rollovers or wind drifted terrain features.  With nearly two feet of new snow,  storm slabs will entrain enough snow to bury you or they can step down into older snow layers producing larger than expected slides. Avoid traveling on steep terrain where slabs will be easy to trigger.  Storm slabs exist at all elevations, but will be very likely near and above treeline where winds have stiffened the slabs.  

Avalanche Discussion

Storm totals this morning range from 8" (.6" SWE) to 12" (1.0" SWE) in the Southeast Mountains and 10" to 19" (1.3 SWE) in the Northwest Mountains. Winds increased overnight during the peak of the storm out of the southwest (Specific details are in our weather tab).  This was a whopping load on a weak snowpack, and it likely produced a natural cycle last night.   With continued snowfall favoring the Northwest Mountains today, coupled with a shift to northwest winds, the threat of ongoing large natural avalanches and very dangerous conditions will continue today. Avalanche activity will be larger and more destructive in this region as well.  In the Southeast Mountains, the peak of loading and snowpack instability has passed but conditions are now primed for dangerous human triggering.  Naturals are possible on wind drifted slopes.  

Our observations page and weekly snowpack summaries tell the tale of a troubled snowpack.  With each loading event in the past two weeks, we have seen an uptick in natural and human triggered avalanches.  This loading event has exceeded previous storms.  The persistent slab problem is not as widespread as it was earlier this month thanks to an abundance of previous avalanche activity and a major wind event which scoured slabs away on some slopes.  However, the stakes are higher now because the slabs are thicker.  Persistent slab avalanches that break on high elevation, leeward start zones in the Northwest Mountains will be large enough to snap trees (D3 in size).  Avalanches that break at lower elevations or in the Southeast Mountains will be large enough to bury you (D2 in size).  

Storm slabs are adding further complexity to the situation.  You can no longer retreat to slopes that already avalanched or to sunny aspects and avoid avalanche problems altogether.   The new snow fell on a variety of weak layers and crusts on all aspects.  The San Juan Mountains picked up more snow than us yesterday, and they saw easily triggered storm slabs throughout the day.  With heavy snowfall and stronger winds shifting towards our region overnight, the same flavor of instabilities has surely developed here as well.  Avalanches that break in the new snow can easily step down and trigger larger slides near the ground on slopes harboring persistent slab structures.   

Avalanche conditions are deadly today.  An AVALANCHE WARNING is in effect.  

 

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