Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
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Limite del bosco
1 · Debole
Sotto il limite
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In sintesi

Look for pockets of wind drifted snow at upper elevations, these will increase in size and sensitivity during the day. It would take the perfect combination of conditions and a dose of bad luck, but you could trigger an avalanche breaking on layers of weak snow in the upper 1 foot of the snowpack. Generally safe avalanche conditions exist where the upper snowpack surface is frozen solid.

Avalanche hazard may increase around sunset as a more intense band of snowfall impacts the area.

 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Periods of light snowfall and variable winds in the past week have built isolated wind drifts in upper elevation terrain. I went out looking for these small slabs on Sunday in the Smoky Mountains, and I found a few (photo at right/above). These slabs I encountered were never more than 6" thick, but they were easy to trigger. As more snow falls today and the wind continues to build these slabs, they will become larger and more sensitive. These slabs pose the greatest hazard to you in areas where being carried downslope at speed would be hazardous. Are there rocks, cliffs, and trees below you? Spend a bit of time thinking about the consequences of being knocked off your feet and sent down the hill. These slabs are also adding weight to the weak layers buried in the upper portion of the snowpack, described below.

    ADDITIONAL DISCUSSION The widespread avalanche activity that occurred in the Banner Summit Zone (north of this zone), and the large avalanche that occurred east of this zone, near Galena Summit last week (photos and details here) are clear indications that the weak layers in the snowpack are nearing their tipping point. I've been looking for this problem for the past two days in the Galena Summit and Eastern Mtns Zone, where the upper snowpack is similar to this zone. In my snowpits, I've received repeated unstable snowpack test scores on an ugly layer of facets and surface hoar buried 10-12 inches deep (Sunday's video here, yesterday's video here,  Sunday's observation here, yesterday's observation here). Additional snow today and tonight will continue to push this layer closer to its breaking point. It doesn't appear to be there quite yet, but it isn't far away. You're most likely to encounter this layer on middle and upper elevation slopes on the northern half of the compass. It will be more sensitive where the wind has added weight and helped to stiffen the slab on top of the weak layers below.

    Read more about the persistent weak layers in the upper snowpack in the Forecast Discussion below. 

    (3/6/2022) This very small wind slab was intentionally triggered with some kicking near the crest of the Smoky Mountains, south of Galena Summit. It failed on an icy crust that formed during the warm weather last week.

Avalanche Discussion

UPPER SNOWPACK COMPLEXITY

We've got a very scientific phrase to describe the upper portion of our snowpack, and I've found myself using it numerous times in the past few days: "Our snowpack is a mess!"  Let's take a look at it and see if we can make a little more sense out of it. 

  • January Drought Layer: Our last major storm drew to a close on January 7th. Oof. Several weeks of cold weather helped to create some prominent facets in the upper portion of the snowpack during this period. This layer is now buried beneath a 6-18" slab across most of our Forecast Area. In the Banner Summit area, this layer produced a number of avalanches large enough to bury you during the storm last week (observation and photos here). 
  • Last Week's Surface: The layer of snow that was buried by last week's warm and wet storm also formed during a period of very cold weather. Unsurprisingly, it also created a number of avalanches in the Banner Summit area.
  • Today's Surface: The snow that is currently at the surface of the snowpack is about to be buried by today's storm. Last week's rainy storm and the very warm days that followed created crusts that extend from the valley bottoms up to 9,500' in places. These crusts tend to concentrate temperature gradients, which promotes faceting in the adjacent snow. Since this layer doesn't have a slab on it yet, it hasn't produced any avalanches. With that said, there is a good chance that you'll be reading about this crust and the associated facets as the snow piles up on top of it in the coming day.s

Avalanches require both slabs and weak layers. As described above, we've got the weak layer component across our Forecast area. The big difference from Zone to Zone is in how thick the overlying slab is. Near Banner Summit, where more snow has fallen in the past 6 weeks, this slab is approaching 1.5' thick. Numerous slab avalanches occurred here during the storm last week and the possibility of human-triggered avalanches is on the table today. As we travel south, the slab of snow overlying these weak layers is thinner and the likelihood of encountering this problem is lower. Today's storm will add a bit more weight to this slab and a bit more stress on the weak layer's underneath. It's difficult to predict exactly when this tipping point will be reached. If it were to snow two feet today my job would be a lot easier, but there is a lot more uncertainty when it only snows a few inches at a time. To deal with this uncertainty, I've already taken a step back from complex avalanche terrain where these weak layers exist. With more snow in the forecast I suspect I'll be continuing to step back as the slab gets thicker and stiffer. 

Today's Forecast is dedicated to Kip Rand, who passed away in the Wallowa Mountains of eastern Oregon on this date in 2016. Kip was a son, a brother, a best friend, a lover, a teacher, and an avalanche forecaster. Take a minute to give a friend a hug today, he'd appreciate it. And don't forget to pack a bag full of cookies for your backcountry travels, there is no better fuel for body and spirit in the mountains. We miss you brother. 

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