Bollettino valanghe

Gunnison

Crested Butte Avalanche Center
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Pericolo valanghe

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

So far, March Meltdown has caused at least a handful of large and dangerous avalanches and many small wet avalanches.  This video from yesterday captures some highlights, including a destructive skier-triggered slab on Gothic.   Temperatures peak today and tomorrow.   The early bird can catch stable corn on southerly aspects before the danger rises to Considerable as the snowpack gets wet.  On colder aspects, the threat of a large slab avalanche breaking on deeper weak layers remains and may be aggravated by surface warming or triggered by shallow wet avalanches and cornice falls.   

Problemi valanghivi

  • Loose Wet

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

    Wet loose avalanches are running naturally or are easy to trigger on almost all aspects and elevations once the top layers of the snowpack get wet.  Most are relatively small, while some can gain volume in longer terrain or could gouge deeper into the snowpack and grow to larger and more dangerous sizes.  Wet avalanches will first develop on steep easterly facing slopes this morning, then move to southerly, then westerly aspects following the sun.  Travel early while the snow surface is frozen or just starting to soften to avoid the problem.   Pinwheels, rollerballs, and natural wet activity are signs that the problem has developed.   Move to lower angle slopes, smaller terrain, or colder aspects once this happens.  

    A wet loose avalanche that started below a steep rock band and gained volume in long, steep terrain

  • Persistent Slabs

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

    In the past two weeks, numerous large to very large slab avalanches broke on weak layers in the upper snowpack and near the ground.  Feedback on the problem is variable and infrequent. Warming snow surfaces may cause the problem to become more sensitive. These issues are most concerning on wind-loaded terrain on colder, shadier aspects highlighted by the persistent slab rose.  Avoid steep, wind-loaded slopes and wind-affected terrain with variable snow depths to reduce your risk.   Persistent slab instabilities are more isolated below treeline; stay alert on very steep or unusually shallow slopes. Southerly aspects typically lack the problem.  

    This large persistent slab ran in Climax Chutes yesterday. It was triggered by  shallow wet loose avalanche and/or surface warming.  Photo: Zach Guy

  • Wet Slabs

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

    Meltwater is increasing concerns for wet slabs to fail as buried weak layers become saturated.  This is a difficult problem to assess or predict, but can generally be avoided by traveling early in the morning while the upper snowpack is frozen.  We have observed a few shallow wet slabs where recent wind slabs got wet on leeward, southerly aspects.  Weak facets a couple of feet deep and depth hoar at the bottom of the snowpack might get flooded to the point of failure on east or west aspects, especially below rocky terrain that amplifies meltwater.   There is typically not enough meltwater into the snowpack on northerly aspects to cause wet slabs this time of year, though exceptions could occur.

    Photo: Zach Guy

Avalanche Discussion

The warmup peaks today and tomorrow.  Clear skies overnight allowed for surfaces to refreeze, and there will be a short window of stable travel on the sunbaked aspects early in the day.  With today's warmer temperatures, wet loose activity will continue to expand to higher elevations and shadier aspects.  Natural wet loose avalanches or cornice falls will run down aspects where we have ongoing persistent slab problems, increasing concerns for large slab releases like yesterday's skier-triggered slide on Gothic or natural in Climax Chutes.  These slabs may become more sensitive from daytime warming, in a hybrid of dry-ish to wetting slabs on east-facing terrain, or dry slabs on northerlies (like this recent D3 on the north side of Treasure).  

Meltwater didn't appear to have reached our most prominent buried weak layers yesterday, but that's becoming more of a concern for today and tomorrow.  Although wet slabs are one of the most challenging problems to predict, spring travel protocols are a straightforward strategy: start early, finish early, and get off steep slopes once you sink to your ankles in wet snow.  Our record-breaking warmup in late February reduced the number of concerning slopes by already flushing meltwater through the snowpack on most southerly aspects.  Historically, wet slabs on northerly aspects are rare this time of year due to the lower March sun angle (ex. 2023 case study). Exceptions might occur at low elevations or on unique slopes where rock bands or topography pipe meltwater.  Our biggest concerns are on those in-betweener aspects, east and west.  East has had a particularly active snowpack structure recently on early March weak layers buried several feet deep.  

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