Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 4 years ago.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

Highlights

You're most likely to trigger avalanches on slopes where the wind has formed drifts or stiffened the snow surface. Large avalanches are also possible in steep wind-sheltered terrain. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Smaller loose snow avalanches may release this afternoon on steep slopes that face the sun. 

Avalanche problems

  • Deep Persistent Slabs

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

    Triggering a 2-4' thick slab avalanche is possible on steep slopes. Persistent weak layers (sugary facets, surface hoar, or crusts) exist on most aspects and elevations. The widespread nature of this weak layer is unusual. Extreme wind over the Solstice reshaped the upper snowpack, thinning (scouring) some areas and building thick hard slabs in others. You're most likely to trigger one of these slides in recently wind-affected terrain. 

    The slab is harder/denser near Banner Summit than in our other zones, making it less sensitive to triggering by skiers and snowmobilers. This means you are not likely to experience obvious signs of instability like snowpack cracking or collapsing. However, if you do find the "sweet spot" remember that you could trigger slides remotely—from gentler terrain above, below, and to the sides of steep slopes. These avalanches may break wider than expected or higher on the slope above you. 

    Unfortunately, avoiding slopes steep enough to slide is the only way to effectively manage this problem. While your odds of triggering a large avalanche are decreasing, the consequences of triggering one are not. Sticking to lower-angled, wind-sheltered slopes is a tactic to effectively reduce your risk.

    ADDITIONAL DISCUSSION: Today's warm weather combined with possible afternoon sunshine may release loose snow avalanches on slopes that face the sun. These should be fairly small but may pile debris deep enough to be of concern below large slopes or channeled terrain. We may also see some rain this afternoon, and certainly this evening which will spread loose snow avalanche activity to all aspects. 

    (12/12/2022) In the Banner Summit zone, the weak November snow is buried beneath a 3' thick dense slab. 

Avalanche Discussion

When writing the forecast in the morning I find it useful to imagine what I'd tell a friend visiting from out of town. And maybe that's you. If it is, props for finding the forecast. Here are the nuts and bolts of what I'd want them (you) to know:

  • Weak snow exists near the ground on most slopes. While the odds of triggering a very large avalanche involving this layer have generally decreased over the last week, this problem still dictates the type of terrain I'm willing to expose myself to. I'm still avoiding steep, consequential terrain particularly W-N-E facing slopes where the combination of weak snow and a thicker slab keep me feeling uneasy. 
  • An extreme wind event on the Solstice largely reshaped the snowpack. It formed slabs on many middle and upper elevation slopes but they also exist on isolated slopes down to the valley bottom. If one were to be triggered today, I'd expect it to be a hard slab that fails on some mix of facets or surface hoar and a crust or ice lens that survived the wind prior to burial. 
  • Uncertainty. In my 10+ years of forecasting, I can't recall a time that I've faced such an odd combination of snow and weather patterns. A widespread weak layer, an extreme wind event, and an Arctic cold front that's followed promptly by a sunny day in the mid-30s F. What will warming, tonight's rain, and tomorrow's temperature in the 40s F bring? That is a great question. Despite having no clear answer, I find solace in a simple rule—as my uncertainty in the conditions increases my appetite for complex or consequential terrain decreases.  

My advice is to remain conservative. The likelihood of a large avalanche is decreasing but the consequences if caught in a slide are not. Personally, that's a game I'm not willing to play. There are enough places to get in trouble out there today, that I'd feel more comfortable sticking to lower-angled slopes, or simple terrain that's disconnected from larger slopes. With that general baseline, I'd steer clear of obvious recently wind-loaded terrain. Not only is wind-sheltered terrain safer today, but the skiing and riding will almost certainly be more enjoyable. Enjoy your Holiday weekend and be sure to check out the latest installment of our Weekend Update!

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