Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

4 to 6 inches of snow overnight and efficient westerly winds drifted terrain on the east half of the compass.  It may be easy for you to trigger avalanches in recently drifted snow at upper elevations; there's a possibility that avalanches break deeper into the snowpack and grow to a dangerous size.  In sheltered areas, a sneaky layer of surface hoar/facets lives 2 to 3 feet deep, and is capable of producing a large avalanche on west to north to east slopes.  You can find a less problematic snowpack on wind-sheltered, southerly slopes or you can manage avalanche hazards by choosing lower-angled slopes on other aspects.

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

    Up to 10 inches of recent snow (past 36 hours) and southwest-to-west winds on Wednesday and Wednesday night formed fresh drifts at upper elevations.  On Thursday, the wind direction may switch to the northwest and increase the distribution of drifted slopes.   You are more likely to encounter sensitive Wind Slabs above treeline, but can still find them near treeline.  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

Incremental snowfall over the past few days and westerly winds keep avalanche conditions dangerous and tricky.  Recent storm totals are up to about 10 inches in the Northwest Mountains and lesser amounts in the Southeast Mountains.  A couple of additional inches and wind loading on Thursday will keep the threat of natural avalanches in the picture on leeward terrain features with active loading.  On Wednesday, observers noted natural avalanches due to recent loading on Scarp Ridge and Whetstone; both of these observations appear to be shallow avalanches releasing deeper and more dangerous slabs.  Avalanches in the recently drifted snow are more likely to 'step down' to the Persistent Slab problem in the Southeast Mountains, but it can't be ruled out in the Northwest Mountains.

In sheltered areas, you will find a problematic layer of surface hoar and facets buried about 1 to 3 feet deep on west through north through east slopes.  The evidence in the Southeast Mountains points to a reactive avalanche problem.  Human-triggered avalanches occurred on Monday, Tuesday, and Wednesday.  Avalanches on this layer have been less common in the Northwest Mountains as the slab is thicker which makes it less sensitive to the weight of a person, but on Monday, an avalanche was remotely triggered near Oh-Be-Joyful low on Schuylkill Ridge.  Even though it may be more stubborn to human triggers in the Northwest Mountains, it remains a threat.  Locations where the slab is thinner, near zone boundaries due to less snowfall, may be more sensitive.  The consequence of triggering an avalanche remains severe as most avalanches will be large.

Avalanche conditions are complex and dangerous on many wind-drifted slopes and sheltered terrain harboring the Persistent Slab problem.  Quality riding conditions can be found on lower-angled terrain and a fresh round of snowfall makes low-elevation southerly terrain a good option for today.

 

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