Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Strong westerly winds and snowfall will create new slabs on leeward terrain at upper elevations and increase pressure on deeply buried weak layers.  Slopes facing the north half of the compass are the most suspect.  You are more likely to trigger a deep failing avalanche on leeward terrain and slopes with variable depth due to wind effects.  Use caution where you find evidence of wind transported snow.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    It is possible to trigger a very large and destructive avalanche today in steep terrain or from flatter terrain where the snowpack connects to a start zone.  These widely propagating and long-running avalanches will break 3 to 5 feet thick or more on weak layers near the bottom of the snowpack.    Persistent slabs are most likely to be trigged on the northern half of the compass, where buried layers are most fragile.  Slabs have grown stubborn to human triggers because of how thick they are.  You are most likely to trigger a persistent slab avalanche where slabs are thinner.  Thin areas are more common in terrain that has seen less snow, or at higher elevations where the wind has redistributed snow into variable snow depths.      

    A recent persistent slab avalanche that broke wide and deep on weak layers near the ground.  

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Westerly winds have drifted snow at upper elevations for several days now, and additional snowfall on Wednesday will help drive further Wind Slab formation.  Expect newly formed slabs to slowly build throughout Wednesday as new snow accumulates.   Look for thicker, denser lobes of drifted snow or blowing snow to identify the problem.  They'll be most common below alpine ridgelines or in cross-loaded terrain features.  A triggered Wind Slab could potentially step down to deeper weak layers particularly in shallower portions of the Southeast Mountains.

    A small wind slab that ran naturally on the south face of Mt. Owen sometime around 1/2.

Avalanche Discussion

Another round of snowfall begins this morning accompanied by strong westerly winds.  This will have a two-fold impact on avalanche conditions.  Firstly, new Wind Slabs are likely to form at upper elevations on leeward aspects and may become quite sensitive to the weight of a person as new snow accumulates today.  6 inches of new snow is a good marker to identify an increase in hazard due to Wind Slab formation.  Expect to find it most commonly below ridgetops, below cornices, and cross-loaded features. 

The second issue with new snowfall and additional wind-loading is the impact on deeply buried weak layers.  The likelihood of triggering a Deep/Persistent Slab avalanche was raised to Possible today to account for uncertainty on leeward terrain features accumulating more wind-driven snow.  Thick, hard slabs that formed over the holidays will likely tolerate substantial new load prior to failing, but this will be the first storm to test these structures.  Slopes that have variable depths due to wind effect, or have slabs around a meter or less thick are most suspect.  Explosive testing at Irwin produced a sizeable avalanche on westerly-facing terrain that was shallower due to the wind stripping away a good portion of the slab from the holiday stormy period.  You can reduce the risk of triggering Deep Persistent and Persistent Slab avalanches by choosing sheltered terrain where slabs are typically more uniform across the terrain and have not received recent or ongoing wind-loading.  

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