Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

You may be able to trigger avalanches up to 2 feet thick where the wind has drifted snow and in protected alpine cirques below steep cliff bands. Expect small, loose snow "sluffs" to release naturally in very steep terrain. Large avalanches are unlikely on slopes where winds are calm and snow is not sifting down from cliffs above.

 

Avalanche problems

  • Wind Slabs

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

    Gusty winds formed thin wind slabs in exposed terrain yesterday. Also, snow "spindrifted" down steep cliff faces and couloirs, forming slabs beneath them. With today's expected snowfall and wind, the slabs could grow up to 2 feet thick and form on more slopes as the day progresses, increasing the odds you'll find them. How will the wind slabs behave today?

    • They formed on a variety of surfaces and could be very sensitive (easy to trigger) on some slopes and stubborn (difficult to trigger) on others. 
    • Where the slabs buried stout crusts or weak snow, avalanches you trigger could be wider than you'd expect. 
    • You may find hard, stiff, and soft slabs. The harder/stiffer the slab, the higher the probability it could break above you rather than at your feet or sled.
    • Slabs could exist near ridgelines, on the sides of cross-loaded chutes and couloirs, and on aprons low in alpine cirques. 
    • The slides could travel very quickly on slick surfaces beneath the new snow. 

    Pay attention to how the snow feels under your skis or boards. If the snow surface suddenly stiffens or becomes more supportable, you've found a wind slab. Cracks shooting out in front of your skis or boards are a red flag warning you to be cautious. Surface clues like dunes or ripples can tell you the wind has been at work.  

    While these avalanches may or may not be big enough to bury people, they could be powerful enough to carry you downslope. Think about the consequences of being pushed around by even a small avalanche before committing to skiing or riding in consequential terrain (above cliffs, trees, lakes, creeks, etc). 

    ADDITIONAL DISCUSSION: The upper part of the snowpack consists of crusts, facets, some isolated surface hoar, melt freeze grains. It's a mess. While I don't expect the recent storm and wind-transported snow to cause several avalanches to fail on persistent weak layers in the upper snowpack, it's not out of the realm of possibility. We've seen a handful of small but interesting avalanches failing on these layers following previous small loading events, and a larger slide occurred last week near Galena Summit (photos and details here). Small changes in aspect or elevation have  big impacts on the snowpack layering and, potentially, stability; the weakest snow we've seen is on the shady half of the compass, spanning upper and middle elevation terrain. Its difficult to accurately predict slope scale stability with these weak layers. 

    (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.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–1.5

    Expect natural and human-triggered loose snow avalanches (sluffs) in very steep terrain (approaching 40*) at middle and upper elevations. Additional snowfall can trigger natural activity, as can even brief periods of direct sunlight on slopes sheltered from the wind.

    While these slides won't be very big, they will be "hauling butt" on the slick surfaces beneath them. The sluffs could easily pack enough of a punch to knock you over or off your machine, carrying you where you don't want to go. Also, there's a chance the small loose snow slides could trigger the larger "spindrift" avalanches described above or a slide that fails on weak layers buried several inches below the new snow. 

    Today is a good day to pay attention to the terrain above you and limit your exposure to hazard from above. If visibility is limited, be careful in—or avoid—serious, complex terrain. 

Avalanche Discussion

CHANGES IN ATTITUDES

After a couple of months of almost no snow, we started seeing some precipitation beginning a week ago. Last week’s warm storm brought enough snow and rain to set off several large slab avalanches near Banner Summit. The culprit was weak snow (facets, facets and crusts, and maybe some surface hoar shards on some slopes?) that formed in January. Additional weak layers formed in February and early March, making the upper snowpack messy and complex. The relative strength of the weak snow, the presence and thickness of crusts or surface hoar, and the characteristics of the slab above the weak snow change rapidly as you move up or down in elevation and around the compass to different aspects. Large slab avalanches are not likely to fail on the upper snowpack persistent weak layers today, but the weak layer and slab spatial variability make it nearly impossible to accurately forecast stability on a given slope.

How do we deal with complex situations like this? KISS: Keep it Simple Stupid/Scotty. The weakest snow in the upper 18” of the snowpack appears to exist on the northern half of the compass (NW-N-NE-E aspects) and spans the middle/upper elevation boundary. Strong winds have prevented widespread weak layers from forming in true alpine terrain, and rain and warm temperatures have “cooked” or melted most potential weak layers at lower elevations. In the “money zone” where the weak snow exists, we (the SAC forecasters) are dialing back our terrain choices. We’re beginning to avoid large or high-consequence starting zones over 35* where the weak layers might exist and a slab has formed in the upper 1-2 feet of the snowpack.  

We’ve seen a handful of interesting avalanches fail on the weak snow in the upper snowpack over the past month. The prudent move is to treat those events as foreshadowing rather than outliers. Each small storm, including today’s, bumps up the chances of avalanches failing on this weak snow and makes me less interested in playing in that terrain until stability/instability patterns emerge.

Regions covered