Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Several days of snowfall and moderate winds have created dangerous conditions at upper elevations. Avoid steep slopes with drifts or stiff snow near the surface. Natural loose snow slides (sluffs) are possible on very steep slopes. An approaching storm will increase the danger this evening.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    With at least a couple feet of fresh snow in recent days, it doesn't take a lot of wind to form slabs. Tuesday, we saw sizable natural avalanches in alpine terrain in the Smoky Mtns (video to right/below, Observation), and snowfall and wind continued since then. Expect to find widespread wind slabs in exposed upper elevation terrain and in cirques beneath large cliff bands. Watch for and steer clear of slopes with drifting and with cornices on the ridges. 

    On very steep slopes, natural and human-triggered loose snow avalanches (sluffs) are possible. This problem is fairly simple to manage—be aware of the terrain above you, especially if it's sunny. Remember that even small slides can have high consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed.

    ADDITIONAL DISCUSSION:In this zone, the December facet layer is buried beneath a very dense, 3-4'+ slab. It would take being in the wrong terrain, as well as a dose of bad luck, to trigger this layer. But if you did trigger a deep slab, you'd need all the luck in the world to survive it. You can reduce the odds of triggering a deep slab by sticking to sheltered, mid-elevation slopes where a more uniformly deep snowpack exists.

Avalanche Discussion

In the past few weeks, snowpack characteristics have diverged significantly across our forecast area. In our northern zones, we are primarily dealing with "new snow" avalanche problems including fresh wind slabs created by new snow + wind as well as loose snow avalanches in very steep terrain. Less snow has fallen in our southern zones and an overall shallower snowpack has kept persistent weak layers or "old snow" avalanche problems at the top of our problem list. Here's a quick rundown to highlight some of these differences. 

Banner Summit and Sawtooth & Western Smoky Mountains:In many ways, the snowpack in these northern zones is simplifying. The rise and fall of avalanche danger here is primarily tied to storm activity. In the last week, a series of storms have deposited anywhere from 2-3.5' of snow (2-2.5" SWE). The ebb and flow of NW wind built wind slabs in exposed terrain. The Banner Summit area, with overall lower elevations and less steep alpine terrain, tends to keep its head out of the wind a little better than the Sawtooths. For this reason, the avalanche danger has remained elevated in the Sawtooths where both wind slab and loose snow avalanche problems are more prominent. 

Weak layers in these zones do exist. In fact, it's likely that the snowmobile-triggered slide near Cape Horn Summit on Tuesday involved a layer of weak facets and surface hoar that we've been tracking since late January. This avalanche (if indeed attributed to this weak layer) bucks a trend of improving stability in the past week. So, as tempted as we may be to toss this avalanche aside as an outlier, that's not how it works—more information is warranted. The primary weak layer of concern in our southern zones, and the one which produced extensive natural and human-triggered avalanche activity earlier this season is buried under a hard 4'+ slab of snow. Triggering an avalanche on a weak layer this deep is unlikely. 

Galena Summit & Eastern Mountains and Soldier & Wood River Valley Mountains:In our southern zones, the waters are much murkier. Here, we're dealing with a highly variable snowpack both in recent storm totals and overall snow depth. The one constant tying these areas together, and what makes them much different than our northern zones is the overall shallower snow depth. In areas where the snowpack less than about 4' deep, our likelihood of impacting weak facets near the ground increase. 

The rise and fall of avalanche danger in these zones is still very much influenced by the presence of weak facets near the ground. It may take less snow + wind to see a spike in avalanche activity and the threat of human-triggered slides can persist for several days after a storm. In these zones, the possibility for small avalanches or cornice breaks to "step-down" to these facets is very real. 

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