Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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

In sintesi

The combination of new snow and wind is building 1-2 foot thick slabs of wind-drifted snow that will be sensitive to your weight today. Look for and avoid steep slopes where these slabs exist. It would take a hefty dose of bad luck, but you may be able to trigger an avalanche that breaks on weak layers in the upper 1-3 feet of the snowpack in very steep terrain that is sheltered from the wind.

Problemi valanghivi

  • Wind Slabs

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

    Today, you are most likely to trigger an avalanche large enough to bury you in terrain that is affected by the wind. A storm is bringing warm and windy conditions with a dose of new snow. This combination will build a fresh round of wind slabs that will be sensitive to your weight. You are most likely to find these slabs in upper elevation terrain but they may extend down into middle elevation terrain as well, thanks to the strength of the wind. Similar slabs formed during a storm on Sunday. Today's snow will make these older slabs more difficult to identify visually, but they may still be reactive.

    Though the forecasted storm totals aren't terribly impressive, there is still quite a bit of loose snow at the surface from Sunday's storm. In combination with today's snowfall, this will give the wind plenty of ammunition for building slabs. Expect to find these slabs along ridgelines and adjacent to cross-loaded terrain features. Look for signs that the wind has been at work and avoid these areas. Pillows and dunes of snow are a great indicator of this. If you are traveling through the terrain here and you find that the snow depth is increasing or that the new snow is becoming denser you've likely found a wind slab. Cracking in these fresh drifts are clear signs of instability. These slabs will be large enough to bury you and should be avoided today.

    Beneath the new snow, several weak layers exist in the upper 1-3' of the snowpack. These layers formed during the dry periods between storms over the past two months. Avalanches that fail on these weak layers are less likely than a typical wind slab, but would be larger and more destructive. You can significantly reduce the likelihood of encountering a slide that breaks on these weak layers by avoiding very steep terrain that has been affected by the wind (steeper than about 35 degrees). Read more about these weak layers in the Forecast Discussion below. 

    ADDITIONAL DISCUSSION: RAIN-ON-SNOW Temperatures will gradually warm this morning and rain may fall up to 7,000' in this zone. If significant amounts of rain are falling on the snow be alert to the possibility of wet loose snow avalanches on very steep slopes. 

    (3/13/2022) This wind slab was intentionally triggered in the Fishhook drainage in the Sawtooths on Sunday. It was 1-1.5 feet thick and failed at the base of the new snow. It failed on an E-facing slope at 8,800'.

Avalanche Discussion

UPPER SNOWPACK COMPLEXITY

It has been a dry few months in our neck of the woods. Small storms have helped to break up this extended drought but have left us with a complexly-layered upper snowpack. The dry periods between storms allowed for a range of weak layers to form and these layers were subsequently buried by the next storm. With each new layer, the character varies significantly as you climb in elevation and wrap around to different aspects. This pattern has been repeated at least half a dozen times in the past 6 weeks. Sound complex? Perfect, I'm doing a good job painting the picture. Read on.

On slopes that face the sun, these weak layers are generally in the form of crusts with associated facets. On slopes that face away from the sun you'll find facets and surface hoar buried at many of these intervals. On the margins between sunny and shady aspects you will find all of these things. A warm storm at the beginning of March brought rain that fell above 9,000' in many areas, adding another weak layer to the mix. Thanks to the variability of these weak layers, assessing the slope-scale presence and stability of any one of these layers is challenging at best, and borderline impossible at worst.

So how do you deal with a problem like this? Well, the answer isn't a terribly satisfying one. The only way to guarantee these layers won't be an issue is to avoid the terrain where they exist. Unfortunately, that describes just about every slope out there. Fortunately, you can significantly reduce your exposure to the hazard posed by these weak layers by choosing gentler sheltered terrain. You're most likely to trigger a slide involving this weak snow on very steep slopes (steeper than about 35 degrees) where the wind has built slabs in recent days and weeks. 

Frustrating? Yes, no doubt about it. Don't worry, I'm right there with you. One of my favorite things to do is to ski in avalanche terrain. I spend hundreds of days each year with skis on my feet. When I can do it safely my preference is to be in steep avalanche terrain. But, my priority is always to come home in one piece at the end of the day. Because of the uncertainty associated with these weak layers, I've taken a step back from steep slopes where these weak layers exist, particularly in places that just had a bunch of snow piled up on top of them. There is lots of good skiing and riding to be found in gentler terrain that hasn't been affected by the wind. It may not be my first choice for this time of year, but it's the only way I can ensure I can head back out again tomorrow.

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