Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
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

The combination of new snow and wind has built a fresh round of reactive wind slabs in upper elevation terrain. Older weak layers are buried underneath dense, 2-4 foot thick slabs of snow that can produce much larger, more destructive avalanches. You aren't likely to experience signs of instability with these deeper weak layers—the first sign may be the large avalanche you trigger. These avalanches can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Choose simple terrain free of terrain traps to reduce your risk.

Problemi valanghivi

  • Persistent Slabs

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

    Layers of weak snow (sugary facets and crust+facet combinations) are buried beneath very dense, 2-4+ foot thick slabs. Triggering an avalanche on these layers is not likely, but the outcome of doing so would be catastrophic. Watch the video to the right/above to get a better feel for this problem.

    These weak layers produced a set of historic avalanches just 10 days ago. Aside from the crowns from these older avalanches, you aren't likely to encounter signs of instability in your travels today. If you don't dig down, the snow will "feel good". But trust me, that weak snow is down there. Don't trust me? Grab your shovel and start digging. 

    Tracks on a slope are not an indication of stability. Avalanches may be triggered after many skiers or riders have traversed a slope. The first sign of instability may be the large, destructive avalanche you trigger. These slides may break much wider and much further above you on the slope than you expect. They can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

    The only way to eliminate your risk of encountering one of these beasts completely is to avoid avalanche terrain and terrain exposed to hazard from above. You can reduce 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.

  • Wind Slabs

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

    Weather stations are reporting 4-8" of snow in this zone, but observations from folks on the ground indicate that much more has fallen in places. Snowfall has been accompanied by moderate winds blowing out of the NW. This combination has built a round of reactive wind slabs in upper elevation terrain. These slabs will be largest, most sensitive, and most dangerous where more snow has fallen. 

    Pay attention to how much new snow you are finding and to the snow you are moving through. If it is becoming deeper and denser you are likely moving through a wind slab. Cracks shooting out from your skis or machine are clear indicators that the slab you've found is unstable. These slabs are building on top of some crusts and facets that developed over the past week. These weak layers may make today's slabs more sensitive than you would normally expect. Yesterday, I found a round of thin but reactive wind slabs in the Smiley Creek drainage. I triggered one small slab remotely while walking on the ridge above. 

    Look for textures on the surface (drifts, dunes, ripples, pillows, etc.) that indicate the wind has been at work. You'll be most likely to find these slabs near ridgelines and on the sides of mid-slope terrain features like gullies and ribs. In the steep terrain of the Sawtooths, slabs commonly form in cirques below large cliff bands and on the aprons below couloirs.  Smaller triggered slides can be effective triggers for the weak layers described in the Persistent Slab problem above.

    ADDITIONAL DISCUSSION: Direct sunshine on fresh snow will produce a round of loose snow avalanches today. These are most likely in very steep, rocky terrain, which is common in this zone. Most of these will be small, but they may pick up speed quickly and pack a punch, thanks to the icy crusts underneath the new snow. 

Avalanche Discussion

As you head out into the mountains today you will be faced with two very different categories of avalanche hazards. At the surface, you'll find fresh wind slabs that will be reactive to your weight and loose snow avalanches that will be easy to trigger and will occur naturally as the sun warms up the new snow. These types of problems are relatively easy to identify and avoid. Further down in the snowpack, you'll find the weak layers that produced the impressive, widespread, and in places historic avalanche cycles earlier in the month. Identifying which slopes may avalanche or where you need to be on a slope to produce an avalanche is essentially impossible. 

You have a choice to make today. Do you want to roll the proverbial dice, or not? Entering avalanche terrain with widespread, well-developed weak layers is a gamble. Today, you are a lot more likely to come out on top in this betting game. The weak layers are deeply buried and impacting them with our weight is not easy. It's more likely than not that you won't trigger a massive avalanche on the slope you are planning on riding or skiing. Unfortunately, if the dice come up snake eyes and you do trigger one of these slides, there is a good chance that you don't survive. 

Dealing with low likelihood/high consequence problems is incredibly frustrating. It is late March and we are all ready for some bigger terrain, but that terrain isn't ready for us. It seems our snowpack must have missed the memo that said it is springtime, as it continues to behave like a mid-winter snowpack with all of the associated avalanche problems. We are well served to follow the snowpack's lead, she is the boss.

I wouldn't be surprised to see ski and sled tracks in big avalanche terrain today. And I won't be surprised if the skiers and riders don't trigger an avalanche there. I also would not be surprised to get a phone call in the middle of the day reporting that a skier or rider triggered and was caught in a very large, unsurvivable slide. Have an honest conversation with your partners and with yourself about the risk you are willing to take to find good skiing and riding today. I don't judge you for the decision you make today, I just ask that you be ready to accept the outcome of that choice. 

Watch Ethan's Weekend Update to get caught up on what happened last week and for a sense of where we are headed this weekend.

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