Bollettino valanghe

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Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

While not likely, you could trigger a 2-4 foot thick avalanche on some slopes. Unfortunately, slides could be very large and unsurvivable. You may be able to trigger avalanches remotely—from gentler terrain above, below, and to the sides of steep slopes. Picture where an avalanche would carry you before committing to skiing or riding steep slopes. 

Problemi valanghivi

  • Persistent Slabs

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

    What is it? You may be able to trigger a 2-4 foot thick avalanche on buried weak layers (sugary facets or crust + facet combinations). Large natural avalanches released last week during the big storms, but the activity was much less widespread here versus in the mountains near and south of Galena Summit. The likelihood of triggering a slide is not that high, but the dense slab makes the consequences severe. 

    Where is it? This problem is worst on middle and upper elevation slopes facing W-NW-N-NE-E-SE. On slopes with multiple or thick crusts in the upper 2 feet of the snowpack, slab avalanches are much less likely. 

    How can you recognize it? Unfortunately, unstable slopes probably will not provide obvious signs of instability like snowpack collapsing or cracks shooting out in front of you. Snowpack stability tests are likely to be inconclusive and are of limited use. In low probability/high consequence situations like this, there's a good chance the first sign of instability you'll see is the avalanche you trigger. 

    How can you manage it?  You can reduce, but not eliminate, your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide. The chance of triggering large avalanches appears to be highest on shadier, more northerly aspects. Persistent weak layers can fail unpredictably and break wider and higher on slopes than you might expect. You may be able to remotely trigger avalanches from gentler terrain above, below, or to the sides of steep slopes. Several people could ride or ski a slope before it avalanches; tracks do not mean a slope is guaranteed to be safe.

    ADDITIONAL DISCUSSION: 

    • While weather stations didn't record impressive winds in the past 48 hours, observers reported seeing some wind-blown snow. Also, E winds can form wind slabs in places you're not used to seeing them. Watch for thin, fresh drifts in upper elevation, wind-exposed terrain.
    • Despite the wintry weather, spring is officially here. As such, even brief periods of sunshine can be intense enough to trigger loose snow avalanches on steep, sun-drenched slopes. Rocky, protected areas with thin snowpacks less than a couple of feet thick are most suspect.

    (3/12/2023) This avalanche failed on a SE slope at 9000' in Lola Creek. Based on the aspect and the appearance of the crown, this slide likely failed on a layer of facets below a melt freeze crust.

Avalanche Discussion

Most avalanche professionals would prefer to travel during HIGH danger driven by Wind Slabs rather than MODERATE danger due to Persistent Slabs. Why is that? Uncertainty. 

Managing the lingering but unpredictable Persistent Slab problem we're faced with is both frustrating and difficult at best. 

  • Following rare, powerful storms like those we experienced last week, slopes that don't avalanche can stabilize rapidly or at a snail's pace.  
  • If we look at 100 avalanche paths, triggering avalanches is not all that likely. But, triggering a large, unsurvivable slide could be very likely on one or more of those 100 paths.
  • We're unlikely to see signs of instability that clue us into which avalanche paths are unstable. We're not getting good feedback to help us figure out which slopes are the proverbial "loaded guns." 
  • The snow generally "feels good" beneath your skis or sled; you're not going to feel that "trap door" sensation of punching through into obvious weak layers. 

So what? Carefully consider the consequences of being caught in an avalanche before committing to skiing or riding steep slopes. If you could be carried through trees or buried deeply in a creek bottom or abrupt transition to flatter ground, the risk-reward probably isn't worth it. You can always choose to take avalanches out of the equation by staying off of and out from beneath slopes over about 30* in pitch. 

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