Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
View on map

Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering an avalanche large enough to bury a person is possible on many slopes. Avalanches will fail on a layer of weak snow that is buried 2-3 feet below the snow surface. You can reduce your risk of encountering such a slide by sticking to lower-angled terrain that is not threatened by steeper slopes above. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. 

Avalanche danger will begin to rise overnight as an intense winter storm impacts our area.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Weak snow is buried beneath a 2-3' thick slab of snow in this zone. This layer of weak snow exists across our Forecast Area and has been the culprit in almost all of the avalanches we've observed in our region this season. You are most likely to trigger an avalanche involving this weak snow in areas where the snowpack is thinner, like in steep, rocky, upper elevation terrain that is affected by the wind. The snowpack is also thinner in the mountains near the mouths of the major drainages above Smiley Creek.

    Immediately south and east of the Zone, where the snowpack is slightly thinner, we are continuing to receive reports of obvious signs of instability. Here is a quick look at some of the red flags from that Zone from the past few days:

    • Yesterday, skiers near the mouth of Baker Creek experienced several large collapses and chose to stick to low angle slopes.
    • Riders across the valley in the White Clouds on Sunday experienced shooting cracks that shattered entire slopes.
    • In the Pole Creek drainage (across the valley) on Sunday, Chris found an unstable snowpack structure and his snowpack tests returned unstable scores (video at right/above).
    • I was in the Owl Creek drainage on Sunday and found an unstable snowpack, experienced cracking and collapsing, and got repeated unstable snowpack test scores in my pit.
    • Observers on Galena Summit continue to report unstable snowpack test scores and a poor snowpack structure.

    These odds of triggering an avalanche have decreased somewhat, but they have not gone away. You can reduce your chance of being caught in an avalanche by avoiding slopes over about 35 degrees, especially those that have been affected by the wind. Given the possibility of remotely-triggering slides, avoid terrain with steeper slopes above you. 

Avalanche Discussion

Yesterday, I used my Forecast Discussion to talk about slabs (link here if you want to get caught up on the two-part mini-series). Today, we will be thinking about weak layers. 

WEAK LAYERS: Up to this point in the year we have mainly had just one weak layer to worry about: the thick stack of facets that we buried in December.  In the professional snow community, we name the layers in the snow based on the date that they are buried. On the 11th of December, after a 3 week stretch of cold temperatures, light winds, and clear skies, this thick layer of weak, early season snow was finally put to bed. And thus, 12/11 was formed. Ever since its burial, 12/11 has caused us nothing but headaches. The general weather pattern that created this weak layer (early season snowfall + early season drought) isn't unusual for our area. However, the weak, faceted snow that developed this year is unique, both in how reactive it has been and how long it has remained reactive. In the six weeks since this layer was buried, it has been responsible for nearly all of the 400 avalanches we've recorded thus far this season. 

There is an interplay between slabs and weak layers. The weight and the characteristics of the overlying slab affect the development of a weak layer after burial. In our northern areas (Banner Summit) the weak snow has been buried beneath a 3+ foot thick slab of snow for several weeks now. During this time, the weak snow has been mechanically compacted by the weight of the overlying slab. In addition, deeper snowpacks tend to create conditions where faceted grains in the snowpack can round and gain strength. Because of this, we are beginning to see signs of healing on the 12/11 weak layer in this area. 

As you travel further south, the slab overlying the weak layer is thinner and the weight has not been enough to significantly change the properties of the weak snow. Also, since the snowpack has remained thin, strong gradients in the snowpack have helped this weak layer to stay very weak. As if that weren't enough, we are also suffering from complications due to the nature of the loading. Instead of putting one big load of snow on at once and giving the weak layer time to adjust, we have gradually built a slab in small doses. This loading style, known as cumulative or incremental loading, tends to help a weak layer stay reactive for extended time periods.

As I write this, a deep low-pressure center is making landfall on the California coast. This slow-moving storm will be impacting our area for the next few days, putting the weak layer to the test. Where the snowpack is the weakest the storm is predicted to be the most intense. If the storm verifies I have no doubt that the snowpack will not be "passing this test". Further north, where less snow is anticipated and the snowpack is stronger, many places may be able to bear the weight of the additional load. Of course, much of this depends on how this storm plays out over the coming days. Stay tuned, we will keep you posted.

Regions covered