Avalanche forecast

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Sawtooth Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
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Out of date — this forecast expired 7 years ago.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 new 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 powerful enough to break trees.

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 hundreds of feet wide, span multiple terrain features and will be powerful enough to snap trees. 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
    Likely
    Size
    1–2

    Over a foot of recent snow and moderate SW-W-NW wind is building fresh slabs in exposed terrain. Yesterday on Copper Mountain, Ben observed wind-blown snow actively forming slabs above a crust. Triggering a wind slab avalanche is likely as moderate wind and snow continue this morning.

    Fortunately, these fresh slabs should be easy to spot and avoid. 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.

The final decision to ski or ride complex, high-consequence terrain is yours. But SAC forecasters and ski guides alike are not ready to put either of these weak layers to bed. As Ben put it a couple of days ago, “we avoided avalanche terrain with buried weak layers; not because we thought triggering a slide was likely, but because we knew it was possible.” For the time being, this possibility is plenty enough to keep me in gentler, simple terrain and on lower angle slopes.

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