Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Avalanche conditions are dangerous in the Southeast Mountains.  Winds are cranking, storm totals are over a foot, and we have a guilty weak layer near the base of the snowpack.  Large natural activity is expected from near and above treeline terrain, and human triggered avalanches are likely.  You can also remotely trigger avalanches from flat terrain below steep slopes.  Carefully evaluate the snowpack before approaching avalanche terrain.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Large and dangerous avalanches breaking into old weak layers will be easy to trigger and will run naturally on northerly and easterly-facing terrain near and above treeline.   Slabs may become reactive today on the same aspects below treeline.   These avalanches have the potential to break wider than you expect, they can be triggered from flat slopes below steep terrain, and naturals could run into low-angled runout zones.  Choose conservative terrain where you find a cohesive slab above weak snow.      

    One of many large persistent slabs that failed naturally during last weekend's storm.  Similar, albeit larger, activity is expected this weekend.

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Storm totals are over a foot deep in the Southeast Mountains.  Slabs of new and drifted snow were easy to trigger and failed naturally yesterday: the problem continues to grow larger today.  Slabs are larger and most sensitive in wind-loaded terrain.  Storm slabs have potential to step down and trigger a larger persistent slab where the problems overlap.  Monitor the size and bonding of storm slabs on small, steep test slopes before riding on slopes steeper than 30 degrees.

    A storm slab triggered yesterday below treeline in the Slate River drainage. 

Avalanche Discussion

As of 5 a.m., 3-day storm totals range from 1 to 3 feet, favoring the Northwest Mountains.  Storm water is 1.6" at Irwin, 1.3" at Schofield, .9" at Butte, and .6" at Upper Tayler.  Winds increased over the past 24 hours and are blowing 20-30 mph this morning, gusting beyond 60 in the alpine.  This illustrates how the most dangerous conditions are in the snow-favored and wind-loaded terrain of the Northwest Mountains, where slabs are the largest and most widespread.  We have documented a clear pattern of avalanches breaking on our early season weak layers with each storm, and our current storm is the most potent yet. Easily triggered avalanches and natural activity are expected across the entire forecast area, especially in windrifted terrain or on shaded aspects with more than about 18" of storm snow.  The avalanche cycle culminates today under peaking wind speeds and the final pulse of snowfall. Although natural activity will diminish tomorrow the threat of human-triggered slides will remain very concerning.  

We expanded the distribution of persistent slabs today to include a few more aspects (SE and W) harboring collapsible crusts at the start of the storm.  It's another persistent weak layer that could produce unusual behavior and remote triggering. That's in addition to our well-documented persistent weak layer that formed during the November dryspell on the northern half of the compass.  We have some uncertainty this morning on whether storm totals in the Southeast Mountains are enough to form reactive slabs below treeline. We errored on the side of caution with the danger rating there, but with careful snowpack evaluation, you may find some slopes are still lacking a slab.  Elsewhere, avalanche conditions are full on today, with high confidence.  

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