Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Very dangerous avalanche conditions exist. Over 2 feet of snow have fallen in the past two days and snowfall will continue today. Avalanches will be easy to trigger, particularly in areas where the new snow is resting on older snow and where the wind has built slabs. Large natural and human-triggered avalanches are likely today and travel in avalanche terrain is not recommended.

Problemi valanghivi

  • Storm Slabs

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

    If you head into the mountains today you will encounter a wide array of avalanche problems caused by the ongoing storm. You are most likely to encounter large avalanches in wind-loaded terrain where older snow existed prior to this storm. On shaded slopes at middle and upper elevations, the new snow is falling on an ugly combination of facets and crusts that developed during the drought of the past month. These facets make for "great" weak layers and the crusts help avalanches that do fail to pick up speed quickly as they travel downslope. Slabs overlying facets can fail in surprising ways, often breaking wider than you might expect and wrapping around terrain features. They also may be triggered remotely—from a distance above, below, or to the sides of steeper slopes. I encountered exactly these conditions yesterday near Galena Summit when I remotely triggered a slide from 30-40 feet away. You can read more about that here.

    While the combination of wind slabs on top of weak layers is the sweet spot for avalanches today that isn't the only place to find them. Over two feet of snow have fallen already in this zone and another 6-10 inches will fall over the course of the day. These rapid rates of precipitation can generate slab avalanches, even on slopes that aren't wind loaded and those that lack a well-defined weak layer. These slabs may be somewhat more predictable than the slabs described above, but they still demand your respect. A 2+ foot thick slab is plenty large to carry you through deadly terrain and bury you. 

    In general, as you climb in elevation conditions will become more and more dangerous. Large human-triggered avalanches are very likely today and travel in avalanche terrain is not recommended. Pay attention to what is above you as well as the terrain you are traveling through—large natural avalanches are likely.

Avalanche Discussion

SPATIAL VARIABILITY AND UNCERTAINTY Avalanche forecasting is rarely simple and clear-cut. That is particularly true on mornings like today. There is a high degree of spatial variability out there, both in the presence and nature of pre-existing snow coverage and in the distribution of snowfall during this storm. Early-season snowfall followed by a long period of above-average (occasionally record-setting) temperatures left us with a highly variable snowpack. Many slopes that face the sun directly lost their snow coverage entirely while shaded slopes at middle and upper elevations developed an ugly mix of slick crusts and facets. The new snow will make it much more difficult to determine which slopes did or did not keep their early season snow. As you move from a slope that was dry two days ago to one that has been holding snow for a month and a half, avalanche conditions will change significantly. This can happen over the span of hundreds of feet or less.

Storm slabs, wind slabs, persistent slabs, loose snow avalanches and cornices...you're going to find it all today if you go looking for it. When we have a high degree of variability and overlapping patterns of old snow, new snow, and wind transported snow, it becomes very difficult to safely navigate avalanche terrain. Add to that the fact that visibility will be poor and your snowpack assessment and terrain management skills are almost certain to be rusty and you have plenty of reasons to dial back your ambition and to stay conservative in your terrain selection. 

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