Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering a large avalanche is most likely on wind-exposed slopes at upper elevations. While less likely, there is a chance of triggering an avalanche in very steep, wind-sheltered terrain. Choosing gentler terrain protected from the wind is the safest option.

Avalanche problems

  • Persistent Slabs

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

    Yesterday, riders in the Baker Creek drainage triggered two avalanches on upper elevation, wind-loaded slopes. They both broke over 100' wide and 12-16" thick and occurred on E-NE aspects near 9500' (photo, photo). While multiple weak layers exist in the upper portion of the snowpack, a thin layer of facets atop a crust is emerging as the top contender. This persistent weak layer seems most prominent on mid and upper elevation slopes facing E-NE-N-NW, although uncertainty exists regarding its overall distribution. This layer was responsible for a small skier-triggered slide on Wednesday near the head of Smiley Ck in the W. Smoky Mountains. In the northern Sawtooths on Thursday, I found it buried beneath a 16" thick slab and received unstable snowpack test scores (video above/right).

    Slopes having the right (or wrong) combination of weak layer and overlying slab are not widespread. In my mind, this is not a good thing! I would rather have unstable conditions nowhere, or everywhere. The spotty nature of the problem makes assessing each slope you want to ski or ride a gamble, and conditions are ripe for getting surprised. 

    You are most likely to trigger a persistent slab avalanche in upper elevation/alpine terrain where the wind has redistributed snow and formed a thicker slab atop the weak layers. But it's also possible to trigger one on wind-sheltered slopes with "prime-time" slope angles steeper than about 35 degrees.  The best approach is to take a step back and choose more conservative terrain. The safest slopes are those protected from the wind and less than 35 degrees in steepness.

    ADDITIONAL DISCUSSION:While cloudier skies are in the forecast today, temperatures will be very warm. It may become possible to trigger small wet slides on very steep (approaching 40 degrees) slopes that face the sun. Pay attention to the tendency for the surface snow to peel away from your skis or sled and slide downhill on underlying crusts.

Avalanche Discussion

The distribution of an avalanche problem describes how common it is within a defined chunk of terrain. Avalanche professionals use a three-step scale to describe this distribution. If the problem is widespread, you'd expect to find it on most, if not all, slopes.  A problem with a specific distribution often exists in terrain with common characteristics—for example, wind-loaded slopes at upper elevations, or on slopes steeper than 40 degrees that face the sun. Last on the distribution scale are isolated problems—these are issues that are not common in the terrain, and there may not be a clear pattern that describes the presence or absence of the problem. 

Clearly you could trigger avalanches in more places when the problem is widespread. So are widespread problems more dangerous? Most avalanche professionals would choose a widespread problem over one with an isolated distribution any day of the winter. Why is that? There is one thing we dislike just as much as mid-winter rain and 2-month dry spells—and that's uncertainty. When conditions are uncertain or unpredictable, it's easy to be optimistic—"oh, conditions aren't that dangerous"—only to get unpleasantly surprised by a triggered avalanche. The best way to manage this is with the following equation: UNCERTAINTY = INSTABILITY. In other words, take a more pessimistic approach. If we can't prove beyond a shadow of a doubt that the avalanche problem doesn't exist on a particular slope, then we consider it guilty.

Catch up on what happened this past week in Scott's latest Weekend Update!

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