Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Up to a foot of snow accumulated in the Northwest Mountains in recent days and gusty westerly winds have drifted the new snow onto easterly aspects.  The most dangerous areas are above treeline due to relentless blowing snow and the deepest storm totals, but don't be surprised to find a wind-drifted slab in open areas at lower elevations.  Your best defense today will be to favor sheltered terrain and simply avoid leeward slopes where sensitive avalanche conditions exist.  In steep sheltered terrain, remain heads up for triggering small loose avalanches in the storm snow.

Avalanche problems

  • Wind Slabs

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

    New snow combined with strong southwest to west winds has created sensitive Wind Slabs. In many areas, these slabs will be small in size, but in snow favored areas of the Ruby Range and the northern Elk Mountains, these slabs could become 14 to 20 inches thick and large in size. This avalanche problem will be the most widespread on the lee sides of ridgelines and cross-loaded terrain features at near and above treeline elevations. This avalanche problem will be less common at below treeline elevations and exist on a few cross-loaded terrain features. A wind slab is classically represented by a rounded or lens-shaped snow deposit, where additional snow has accumulated on the lee side of the terrain feature.  Shooting cracks, active snow transport, and fresh cornice formation all point to Wind Slab formation.

    4/13 - A small triggered Wind Slab from Wednesday below a roll in a near treeline basin.  Expect big, leeward slopes in the alpine to be capable of producing much larger avalanches than pictured here.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2

     Slab avalanches breaking into old weak layers several feet deep have become unlikely, but not impossible.  Higher elevation, northerly facing terrain still holds a dry, winterlike snowpack; thus we can't completely eliminate the potential for a rare but large slab avalanche on these aspects.  The most suspect terrain is where snow coverage is shallower,  especially on convex, unsupported slopes or near rock bands. You are most likely to trigger a slide from a shallower spot on the slope.  If you are skiing or riding in that type of terrain, reduce your group's exposure during uphill travel and choose appropriate safe zones from a large avalanche while descending.  Let your friend wrestle their stuck snowmobile off of suspect slopes by themselves.  

    Example of our most recent persistent slab avalanche that likely failed around March 30th.  This large avalanche highlights the type of terrain that remains most worrisome:  northerly, rocky, and unsupported.  

Avalanche Discussion

The new snow and strong westerly winds are driving the dangerous avalanche conditions on leeward terrain at upper elevations.  The most dangerous conditions are in the Northwest Mountains, particularly the Ruby Range, where the most snow has fallen over the past two days.  The Southeast Mountains picked up less snow, so conditions are less dangerous to a small degree due to smaller size Wind Slabs.

Winds have been blowing consistently since snowfall began in the early morning hours of Tuesday.  Take a look at data from the Irwin Guides Ridge Top weather station to see evidence of the relentless 20-30 mph winds commonly gusting more than 40 mph.  Yesterday, CBAC forecast staff observed a density change near the bottom of the storm snow that is helping to create sensitive avalanche conditions on drifted terrain.  Additionally, there were several natural avalanches observed and two intentionally triggered Wind Slabs (you can see images in the gallery below).  It took very little effort yesterday to find and trigger a Wind Slab on leeward terrain; expect sensitivity to remain similar today.  Anticipate that some terrain features, particularly those with a large, efficient fetch, to potentially produce large-sized avalanches that are big enough to bury, injure, or kill you.  The simplest and most effective management technique will be to identify and avoid leeward terrain features and stick to sheltered areas where the wind is far less likely to form slabs.

In sheltered terrain, you may be able to trigger small loose avalanches on very steep slopes.  Several observers noted triggering 'sluffs' in the new snow on the steepest pitches (ob 1, ob 2).  Loose avalanches in the storm snow are expected to remain small in size but could push you into rocks or trees.

Regions covered