Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You’re most likely to trigger a slab avalanche where wind and recent snow has combined to form fresh drifts at upper elevations. While less likely, it’s possible to trigger an avalanche on older weak layers buried 2-3 feet deep. These layers are widespread at middle and upper elevations and the resulting slide will be large enough to bury you. A powerful storm will increase the danger overnight and into the weekend.

Avalanche problems

  • Persistent Slabs

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

    Newly fallen and wind-blown snow continue to add stress to persistent weak layers buried 2 to 3 feet deep. These layers are widespread at middle and upper elevations and are responsible for the majority of recorded avalanches so far this season. 

    An avalanche failing on one of these layers has the potential to break wider than expected, span multiple terrain features, and will include the majority of the snowpack. Slides may be triggered from a distance and have the potential to pull back into low-angle terrain near the top of a slope. 

    It’s a safe bet to assume one or both of these layers sit beneath your boards or sled. To reduce the chances of triggering a slide on these layers I’ve been steering clear of obviously wind-loaded terrain and sticking to gentler, lower angle slopes.

  • Wind Slabs

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

    Over a foot of recent snow and moderate SW-W-NW wind built fresh slabs in exposed terrain. Wednesday on Copper Mountain, Ben observed wind-blown snow actively forming slabs above a crust. Yesterday, observers in neighboring zones reported cracking in small, freshly formed wind slabs and drifts. 

    These drifts can be particularly touchy where they lie above slick, hard, wind-buffed surfaces or the persistent weak layers described above. You’re most likely to encounter this problem near ridgelines at upper elevations. Cracks shooting from your boards or sled are a sure sign that you’ve found a sensitive slab.

Avalanche Discussion

Well, here we are again. If you’ve been around Central Idaho (or more generally the Intermountain West) long you’ve come to expect these stretches when we deal with persistent weak layers that linger for weeks or even months at a time. As a forecaster, it's a tough situation to be in. It’s much easier for us to tell you when it’s generally safe, or the opposite, when the mountains are coming crashing down. On average, however, we often bounce around in this middle ground where triggering a destructive avalanche isn’t likely but the possibility is certainly on the table. 

Our two primary weak layers are buried near the middle and base of the snowpack; surface hoar (or crust + facets in some areas) and depth hoar, crusts and facets near the ground. A recent Instagram comment asked how and when we can expect these weak layers to finally go away? In a nutshell, weak layers that are more deeply buried will tend to gain strength, in part due to the weight of the overlying slab and part due to the low temperature gradients that encourage rounding. In some areas, where these weak layers are buried 2-3’ deep, snowpack test scores have pointed to these layers gaining strength, but we’re not out of the woods yet. In shallower areas, we’re still experiencing collapsing, and these weak layers have improved very little.

Hopefully, we’ll have a larger body of evidence to pull from after the upcoming series of storms. I say “hopefully” because there’s an overarching “well, I guess we’ll wait and see” mentality to our conversations leading up to this storm. It’ll be interesting to see what slides and what doesn't, of course, a lot of this activity is tied to how much snow we get, where it falls, and how fast. Given the spatial variability of the current snow depths, slab properties, and weak layers, the outcomes may vary drastically over a short distance. While these weak layers are put to the test, take a big step back and record what you see—the next several days should be interesting.

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