Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanches are unlikely, and most slopes are safe. Watch for small, isolated wind drifts in upper elevation and alpine terrain

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1

    On Saturday, 1-2" of new snow fell in this zone accompanied by moderate to strong winds blowing out of the SW-NW. Yesterday, professional observers in the Western Smokys reported finding small slabs that were reactive to ski cuts. Chris was in the Sawtooths and reported seeing very small, thin slabs that had failed naturally in areas where snow trickling down from cliff bands above had helped to build slabs. None of these slabs were large enough to bury a person, but they could knock you off your feet and send you tumbling down the slope. Since you are most likely to come across one of these slabs in steep, rocky, upper elevation terrain such a fall could have high consequences.

    Hidden below these thin fresh slabs is an older generation of wind slabs that formed during last weekend's storm. In most locations, these slabs have had time to bond to the surfaces they were deposited on. However, the combination of sun crusts and facets can create weak surfaces that act as longer-lived weak layers. This exact combination was the culprit weak layer in a wind slab that was triggered in this zone on Tuesday (photo at right). Encountering a sensitive slab from last weekend's storm is most likely on the northern half of the compass, particularly on the eastern and western margins where faceted snow grains are paired with a subtle sun crust. Look for drifts of stiffened snow that produce cracks that extend past your skis, board, or machine, a telltale sign of a sensitive wind drift. 

Avalanche Discussion

The potential for avalanches only truly goes to zero once the entire snowpack has melted. In light of that, continue to exercise caution when traveling in the backcountry. What does normal caution look like?

  • Make a solid plan before a day in the backcountry. A plan helps you anticipate hazards (of which avalanches are only one), identify options for the day, and ensure everyone is prepared for an emergency.
  • Perform a trailhead gear check. A proper beacon check ensures everyone's transceiver can send and receive a signal. Maybe you could use a brush-up on your beacon skills? Don't forget about the Baker Creek beacon park. Is everyone's radio working and on the right channel? Airbags armed and in working order?
  • Maintain situational awareness. Don't let your guard down even when the snowpack is generally stable. If you see a wind-loaded slope or another indicator of potential instability, don't assume it's safe just because the danger is Low. Identify and avoid other hazards such as large cornices. 
  • Communicate with your partners. As you travel through the mountains talk with your partners. Are you seeing what you were expecting to see when you made your plan in the morning or are conditions different than you thought that they would be? Do you need to adjust your plan accordingly?
  • Continue to use safe travel practices. It's easy to get sloppy with your travel practices during periods of stability. Continue to minimize your group's exposure to potential avalanche hazards, ideally traveling one at a time through steep terrain.
  • Minimize your exposure to hazards. The likelihood of encountering any sort of problem in life increases when you spend more time exposed to that hazard. You are more likely to be involved in a car accident if you drive every day of the year than you are if you only drive once a week. The same is true in the backcountry. 

LOW DANGER AS A LEARNING OPPORTUNITYWhen the avalanche danger is low we are able to access a lot of terrain that is off-limits during periods of elevated avalanche danger. And while we're all eager for more snow to fall (guilty), we can use this period of low danger as a learning opportunity. There are processes taking place in the snowpack that we can directly observe if we take the time to look for them. Here is a homework assignment for you: when you're out in the mountains today I'd like you to mentally map the distribution of surface conditions you are finding. There are three obvious things to look for:

  1. Wind Slabs: The dusting of snow that fell this weekend provided some fresh ammunition for the winds. Look for where the wind moved this snow from and where it moved it to. Where are these drifts the thickest? If you are finding a drift that is 6" thick when only 1" of snow fell, what does that tell you? Would you be surprised to find drifts several feet thick after a foot of snow falls? Make mental notes of these things and use them to help you manage the next wind slab problem that you are faced with.
  2. Crusts: Significant amounts of direct sun in the past weeks have altered the snow surface significantly. When you are traveling on a slope that directly faces the sun, pay attention to the crusts that you find. Is it strong enough to hold you up ("supportable") or are you sometimes walking on top of it and sometimes falling through it ("breakable")? What affect does the slope angle have on this crust? Is it more supportable on steep slopes or on shallow slopes? What about on the eastern and western margins of the compass? Are the crusts thicker or thinner here? You can use your mental crust map to help you choose slopes where the riding quality is still good, even weeks after the last snowfall. 
  3. Facets: As you travel on slopes on the north half of the compass, you'll find that sun crusts disappear. What is the snow surface like in those areas? Does it feel strong (easy to skin through, make a snowball out of, etc.) or does it feel weak (sugary grains that you slip and slide on when you are skinning and that you can't make a snowball out of)? Pick up some of the surface snow and rub it between your fingers when you have your gloves on. Does it have a gritty, sandy feeling to it? Compare this to the skiff of fresh snow that fell this weekend. How does it feel underneath your sled or bike? Are you riding on top of the snow (strong) or when you goose the throttle does the tail end of your machine drop to the ground (weak)? Facets, particularly when paired with crusts, make for "great" weak layers. 

When it snows again think about the mental map that you just created. In conjunction with the avalanche forecast, you can use your map to help you seek out areas where the snow stability and riding conditions are at their best.

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