Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Another round of snowfall and west winds keep avalanche conditions dangerous.  You are likely to trigger an avalanche in recently drifted snow and on persistent weak layers deeper in the snowpack.  Natural avalanches are possible on slopes with active wind loading (like this natural on Whetstone yesterday).  In sheltered terrain facing west to north to east, a layer of surface hoar and facets 1 to 2 feet deep is sensitive to the weight of a person, and triggered avalanches are likely.  You can find less risky options on wind-sheltered southerly slopes or you can manage the avalanche hazard through lower-angled terrain selection everywhere else.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    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 1 to 2 feet thick over these weak layers are sensitive to 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.  

     

    A fresh natural avalanche on Whestone's Hidden Lake Bowl.  It appears as though a shallow Wind Slab at ridge top released a deeper slab below the cliffs as it ran.  This type of avalanche activity should be expected in the Southeast Mountains on drifted terrain highlighted by the Persistent Slab rose.

    Photo: Jake Hutchinson

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Up to 7 inches of recent snow (past 36 hours) and southwest-to-west winds formed drifts on leeward terrain.  On Thursday winds may shift to the northwest and increase the distribution of drifted terrain.  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 potential for wind slabs to step down and trigger a much larger persistent slab avalanche, like this recent avalanche on Mt. Owen or this avalanche on Whetstone. 

    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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