Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

Mother nature will be hitting the mountains hard this morning, with quickly accumulating snow and continued strong winds. The avalanche danger will be rapidly rising at the same time. The most dangerous areas will be wind-loaded terrain at near and above treeline elevations. Problematic wind-loaded terrain can also be found on a few below treeline slopes as well. In wind-sheltered terrain, keep your eye out for the potential of small storm slabs developing in steep terrain where you find about 6" or more of new snow. 

Problemi valanghivi

  • Wind Slabs

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

    New snow combined with strong southwest to west wind will create sensitive wind slabs. In many areas, these slabs will be small in size, but in snow favored areas of the Ruby Range and the northern Elk Mountains, these slabs could become 12 to 18 inches thick and large in size. This avalanche problem will be the most widespread on the lee sides of ridgelines and cross-loaded terrain features at near and above treeline elevations. This avalanche problem will be less common at below treeline elevations and exist on a few cross-loaded terrain features. A wind slab is classically represented by a rounded or lens-shaped snow deposit, where additional snow has accumulated on the lee side of the terrain feature. 

    An example of a shallow wind slab from earlear this winter. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2

     Slab avalanches breaking into old weak layers several feet deep have become unlikely, but not impossible.  Higher elevation, northerly facing terrain still holds a dry, winterlike snowpack; thus we can't completely eliminate the potential for a rare but large slab avalanche on these aspects.  The most suspect terrain is where snow coverage is shallower,  especially on convex, unsupported slopes or near rock bands. You are most likely to trigger a slide from a shallower spot on the slope.  If you are skiing or riding in that type of terrain, reduce your group's exposure during uphill travel and choose appropriate safe zones from a large avalanche while descending.  Let your friend wrestle their stuck snowmobile off of suspect slopes by themselves.  

    Example of our most recent persistent slab avalanche that likely failed around March 30th.  This large avalanche highlights the type of terrain that remains most worrisome:  northerly, rocky, and unsupported.  

Avalanche Discussion

The arrival of accumulating snow is several hours behind what was previously forecasted and is just now ramping up this morning. Continued strong winds with periods of heavy snowfall are expected to raise the avalanche danger from LOW to CONSIDERABLE. Wind slab avalanches are the primary avalanche problem today and are expected to remain the primary avalanche problem in the coming days. The persistent slab avalanche problem remains unlikely and the additional weight of this new snow isn't expected to notably change the sensitivity of that avalanche problem. 

A storm slab avalanche problem didn't make the list this morning. If we see the upper end of forecasted snow in the NW Mountains I wouldn't completely rule out the possibility of soft slabs forming in wind sheltered areas. The temperature trend is mostly decreasing during this first round of snow. That is a good thing that will help create right-side layering. However, the turbulent nature of this storm will likely have created layers of graupel that have accumulated within the storm snow. So we could see some slopes in the snow favored areas develop a shallow storm slab avalanche problem if enough snow accumulates on these potential weak layers. Accumulating snowfall is expected to taper off this afternoon and remain fairly light tomorrow. However, the winds remain moderate to strong over the next few days. In general, the avalanche danger will decrease heading into Wednesday. However, contenued wind-loading may keep the danger elevated in the snow-favored areas of the NW Mountains. 

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