Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Tue
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3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
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In sintesi

Numerous large natural avalanches released in the last few days from increased winds, and collapsing snowpacks have been relentless at lower elevations.  Slabs are often an ideal depth for human triggering, and remain sensitive where they formed over the shallow and weak snowpacks left behind in steep terrain by the Thanksgiving cycle.  Conservative terrain choices on west, north, east, and high elevation south aspects are essential. The safest riding is on slope angles under 30 to 35 degrees or wind-protected southerly slopes. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2.5

    Slabs averaging 1 to 2 feet thick in sheltered terrain and larger in wind-loaded terrain are still sensitive to triggers where they formed over well-developed facets and collapsible crusts on west, north, and east aspects. Additionally, wind-loaded slabs have been failing above buried crusts on high elevation, southerly aspects. Slab behavior is challenging with variable and deceptive feedback, remote triggering potential, and wide propagation across terrain features.  You can reliably avoid the problem on slope angles less than 30 degrees without steeper slopes above you, and most mid to low-elevation southerly aspects lack the problem.  

  • Wind Slabs

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

    There is lingering potential to trigger a shallow wind slab on leeward slopes to northwest windloading patterns.  Look for cracking on and stiffer deposits below ridges, rollovers, and in gullies to identify features of concern.  Most slabs should be small in size (up to D1.5) but large enough to cause harm in terrain traps.  These slabs will be most dangerous in high-consequence terrain or if they step down and trigger a larger persistent slab described above.  

    An example of a shallow wind slab (top left part of the slope) that stepped down and triggered a larger persistent slab near Twin Lakes.

Avalanche Discussion

Northwest Mountains: The Northwest Mountains took a quick hit with 8" to 18" of snow on Saturday, and with good visibility yesterday, we did not see any step-down avalanches from the numerous small storm instabilities.  This is one more small piece in the snowpack puzzle pointing towards the persistent slab problem becoming stubborn on most slopes and remaining reactive on a few slopes, thus "possible." (Read more about how we define possible here).  Moderate danger means heightened avalanche conditions exist on specific terrain features.  Those specific features can be difficult to identify and carry serious consequences with persistent slabs, so avoiding slopes where the problem exists is often the simplest and most reliable strategy. Our avalanche records from the last three weeks show a strong pattern of the aspects and elevations that are most troublesome. However, if you are traveling in terrain highlighted by the persistent slab rose, here are the more specific terrain snowpack/terrain characteristics that sound my "Retreat! Retreat!" alarms. 

  • N/BTL: I'm especially nervous of slope angles steeper than 35 degrees where the snow depth is less than 4 feet (120 cm) and where the holiday slab is still preserved without recent avalanche activity or northerly wind erosion.  When these ingredients overlap with a large slope or funnel into a terrain trap such as trees or a gulley, that's a no-go. 
  • ATL: Slopes that have seen more consistent wind loading than wind erosion in the recent week, especially in terrain where slabs thin out, have rocky, shallow areas, or are typically thin but saw unusual loading from our northeast wind event. These slides on Baldy are a good example.

Southeast Mountains: Well dang, we sure sound like a broken record. Dangerous avalanche conditions continue, evidenced by easy and frequent collapsing at lower elevations (watch this video from yesterday; sound on for awkward, heavy breathing). That, and the spree of large natural persistent slab avalanches in the alpine that ended Sunday morning when northerly winds finally eased up.  Under quiet weather this week, we will see improvements in the shallow zone as well, just at a slower pace. Slabs are starting to decay in the shallowest areas below 10,000', and those wind loaded slopes up high will have a chance to catch their breath after the abusive wind events since Thursday.   Lower slope angles, mid to low-elevation southerlies, or slopes that have lost their slab from wind erosion, faceting, or recent avalanches are your best friend.  

Events:  Our next Fireside Chat is this Thursday, 7 p.m., at the billy barr lounge, where Danielle Beamer will discuss Mental Health and Backcountry Decisions.  The event is free and open to all.  

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