Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Strengthening winds today and heavy snowfall rates this evening are increasing the avalanche danger.  Watch for changing conditions and blowing snow alerting you to fresh wind slab development and the potential for natural avalanches.  In wind-protected terrain, there's a layer of surface hoar buried two to three feet deep, capable of producing large avalanches on west, north, and east facing slopes steeper than about 35 degrees.  This remotely triggered avalanche on Monday is a good example.  The safest riding is in wind-protected terrain on the south side of the compass, or on lower slope angles elsewhere.  

Avalanche problems

  • Persistent Slabs

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

    A new round of weak layers was buried on February 2nd. These weak layers consist of widespread surface hoar and facets on most east, north, and west-facing slopes, and along with some faceted crusts on higher elevation southerly aspects. Slabs about 2 to 3 feet thick over these weak layers are becoming more stubborn, but can still be triggered by skiers and riders. This avalanche problem can be remotely triggered from flat terrain, or may propagate further than expected.  Shooting cracks or collapses are a clear sign of danger, but these obvious signs of instability will not always show themselves before an avalanche releases.  There is isolated potential to trigger older, larger slabs on weak layers deeper in the snowpack, most likely from shallow terrain features or step-down avalanches.  

    You can reliably avoid trouble on terrain with slope angles less than 30 degrees that are free from overhead steep terrain. Lower elevation southerly aspects offer safer options for steep terrain.  

     

    2/19:  A remotely triggered persistent slab above the Slate River

  • Wind Slabs

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

    2" to 5" of new snow and strengthening winds out of the southwest will form sensitive wind drifts above treeline and on some near treeline slopes.  Wind slabs will grow in size throughout the day, especially in areas that have more fresh snow available for transport.  Look for blowing snow and stiff, dense drifts to identify the problem.  Drifts will be forming below cornices, leeward ridgelines, and in gulleys or concave catchments at higher elevations.     There is isolated potential for wind slabs to step down and trigger a much larger persistent slab avalanche, like this recent avalanche on Mt. Owen. 

    This recent wind slab triggered at Irwin exemplifies the type of wind slabs we are expecting to see today.

Avalanche Discussion

Wind drifting will increase the avalanche danger throughout the day.  Most of the region only picked up 1" to 2" of dense snow, and snow available for transport on windward aspects is relatively small.   However, Schofield Pass has picked up 5" (.6" SWE) already, so wind transport is expected to be more significant in some parts of the Northwest Mountains.  It will be an unpleasant day to be romping around in the alpine, but if you are, watch for fresh wind slab formation and the increasing threat of larger naturals involving our buried persistent weak layers.  The threat of persistent slabs releasing naturally is most acute in the Southeast Mountains, where the snowpack has proven to be most sensitive to small loading events.   In the Northwest Mountains, a period of heavy snowfall this evening will further increase the danger shortly after sunset, and could be enough to expand dangerous conditions to near treeline elevations tonight.  Keep an eye out for that pulse showing up earlier than expected later today.  

If you are seeking asylum from the wind, you need to manage for the threat of a troublesome layer of surface hoar buried 1 to 3 feet below the snow surface on the north half of the compass.  In the shallower Southeast Mountains, that layer continues to be reactive to human triggers.  Our forecast team near Snodgrass yesterday intentionally triggered several large persistent slabs (see video).  On Monday, a snowmobiler in Cement Creek remotely triggered 5 persistent slabs from an impressive distance.  In the deeper Northwest Mountains, the layer is buried deeper and is more stubborn, in general. This forecaster observation from the Marble side describes the situation in the most snow-favored parts of the Northwest Mountains.  As you move away from the snowbelt, such as the Beckwith Range, or near the zone boundaries, slabs are thinner and more sensitive, exemplified by this avalanche triggered on Monday above the Slate River.  

Regions covered