Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering an avalanche that fails on weak snow buried 3+' deep is possible on many slopes. You are most likely to trigger one of these monsters in steep, rocky, upper elevation terrain that is affected by the wind, but avalanches are possible in terrain sheltered from the wind as well. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. 

Avalanche problems

  • Deep Persistent Slabs

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

    The same layer of weak snow that exists in our other zones also exists in the Banner Summit Area. The big difference here is that this snow is buried beneath a dense, 3+ foot thick slab of snow. This slab of snow is "protecting" the weak layer, making it more difficult to trigger an avalanche on it. However, if you are unlucky enough to trigger a slide it is going to be large enough to snap trees and leave piles of debris many, many feet deep. If you're anything like me, that doesn't sound like something you want to encounter. 

    I visited this zone yesterday to look for this problem and see how it is progressing over time. I explained what I found in this video available here. When I was out there I also observed evidence of very large deep slab avalanches that failed during the storm last week. The photo at right/below shows one of the slides that I observed. 

    Deep slabs behave unpredictably, often failing after many riders have already traveled on a slope. Tracks on a slope are not an indication of stability. You are most likely to trigger one of these monsters in steep, rocky terrain at upper elevations. In these areas, thin spots in the snowpack created by wind scouring bring the weak layer closer to the surface. The best—and often only—way to manage a deep persistent slab problem is by sticking to lower-angled terrain. Given the possibility of remote-triggering, you'll also want to avoid being below steep slopes that have these characteristics. 

    (1/18/2021) This very large avalanche occured in our Banner Summit Zone, likely during last week's storm. Based on the depth and appearance of the crown it probably failed on facets buried near the base of the snowpack.

Avalanche Discussion

One important variable that we consider when assessing avalanche hazard is the amount of time that has elapsed since a load was placed on the snowpack. In our case, the last major snowfall occurred six days ago. Following this storm, strong to extreme winds easily pushed around the snow that fell. In some places, winds were strong enough to blow the snow off into the atmosphere while in others it loaded slopes. This additional loading produced a second round of natural avalanche activity. It has now been a few days since we've observed active wind-loading, which has given the snowpack a bit of time to adjust to the additional stress.

Generally, a few days without loading is a healthy break for the snowpack. If we were dealing with a strong snowpack without weak layers, the avalanche hazard would lower right now. However, the sugary, faceted snow buried near the ground in our region is anything but strong. This widespread layer of weak snow has been buried for over a month, and each time we add more weight with a storm we see widespread natural avalanche activity. Equally importantly, each time we add a trigger to the mix (riders, skiers, you!) we are seeing human-triggered avalanches continue many days after loading. Our snowpack doesn't need a weekend off, it needs a long vacation on the beach. 

The backcountry is what is known as a "wicked learning environment." Environments like this provide feedback that is either difficult to interpret or altogether nonexistent. For example, your partner decides to ski a steeper line than you had agreed upon and nothing bad happens. Does that mean that the slope was actually safe and that the decision was a good one? Well, no. And therein lies the problem—the only direct feedback that we get from the snow is when it avalanches. The absence of an avalanche is not a sign of stability. And once we trigger an avalanche we have set ourselves up to learn some hard lessons.

Today will be a beautiful, calm, sunny day. The lure of steep, untracked slopes will be strong. But the weak snow that is buried in our snowpack is not in any hurry to heal and today is not significantly safer than yesterday. We continue to encourage you to make your decisions in the backcountry with this weak snow in mind.

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