Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

With smaller storm totals, the most dangerous conditions in the Southeast Mountains are in wind-affected terrain near and above treeline.  Slabs of freshly drifted snow will be easy to trigger on leeward slopes, and wind-affected terrain is where you are most likely to trigger a large slab that breaks into deeper weak layers.    Instabilities are generally smaller and less common in wind-protected terrain at lower elevations, especially on southerly aspects.    

Problemi valanghivi

  • Wind Slabs

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

    About 6" of new snow and continuous northwest winds since Friday night have formed wind drifts on leeward terrain features.  Fresh drifts will be most sensitive where they formed over fragile weak layers on the north half of the compass.  Although most wind slabs will be relatively small in size, terrain with larger fetches will have thicker and larger slabs. Carefully evaluate slab size and terrain consequences before riding near wind loaded terrain.  Cracking or collapsing is a clear sign of unstable snow.  Fresh wind slabs could be remotely triggered because they are forming on surface hoar.   Instabilities in the upper snowpack have the potential to step down and trigger larger and more dangerous persistent slabs where the problems overlap.  

    The new snow is accumulating on weak layers of surface hoar (shown here) and near surface facets on west, north, and east facing slopes, and crusts on southerly slopes.  

  • Persistent Slabs

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

    The recent storm will make old layers deeper in the snowpack more susceptible to human and natural triggers than earlier this week, especially on drifted slopes.   Persistent slabs up to several feet thick have the potential to fail widely or be remotely triggered from near or below steep slopes.  These dense old slabs may not give warning signs before releasing, but collapsing and cracking are sure signs of danger.   The problem is less concerning on wind sheltered southerly aspects where the recent warmup created thick surface crusts (see video).   The easiest and most reliable way to manage this problem is to ride on slopes consistently less than 30 degrees in steepness.  You are most likely to trigger a persistent slab where the snowpack is shallow or variable in depth, or if you trigger an avalanche in the new snow that gains enough mass to step down.  

    An example of a large persistent slab that ran earlier this week in the Elk Mountains.  The current loading pattern will make avalanches like these more likely to fail.  

Avalanche Discussion

Conditions vary significantly across the forecast zones due to significant differences in storm totals.  Read our weather forecast for details on which areas received the most snow and will have the most dangerous conditions today. 

Northwest Mountains: Tell Mother Nature it's underproducing, and it will laugh in your face.  The storm escalated in the Northwest Mountains yesterday and overnight, producing up to another 20" since yesterday morning's report.  In the favored Ruby Range, the danger rose to HIGH overnight and a large natural cycle likely occurred.   We are just coming off of the wind and snow loading period this morning, and conditions are just crossing back towards CONSIDERABLE.  Natural avalanches could continue from solar warming or light wind drifting today, and they'll be very sensitive to triggers at all elevations.  Yesterday, skiers and riders easily triggered fresh slabs 12" to 18" thick breaking on the facets and surface hoar layers that are widespread on west, north, and east aspects.  Those slabs are now up to 2 feet thick below treeline, and larger on wind-drifted slopes.  These new slabs will start behaving more erratically today, with wider propagation and longer remote trigger potential.  With storm totals as high as 3.2" of SWE, avalanches stepping down into older weak layers are a serious concern.  Though the peak of instability occurred before sunrise this morning, we recommend avoiding avalanche terrain today. It's going to be falling apart out there for skiers and riders.  

Southeast Mountains: Smaller storm totals (~6") make for a less dramatic change in conditions.  The biggest driver is the constant wind drifting over the past 36 hours. The shallow zone always produces with productive wind transport, so I expect we'll see natural activity as well, just not as widespread and more confined to wind drifted features.  The persistent slab problem has also shown a pattern of waking up every time we see snow transport this winter; there are more slopes in our shallow zone with a shallower and weaker snowpack that will become reactive to the additional loading from the wind drifting.  Observations from below treeline suggest there wasn't quite enough snow to create storm slab problem yet, but monitor for cracking or collapses to look for outlier conditions.  

Events: Our next Fireside Chat is TODAY at 6 p.m. at High Alpine Brewing Company in Gunnison. A local snowmobiler will talk about his experience with an avalanche burial and rescue while snowmobiling last year.

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