Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
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Out of date — this forecast expired 6 years ago.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

A foot of new snow fell yesterday at upper elevations in this zone, with a bit more expected today. Isolated wind drifts exist on upper elevation slopes, where triggering a 1-2 foot thick avalanche in steep terrain is possible. In very steep, sheltered terrain, loose snow avalanches are also possible. And while unlikely, we can't rule out triggering an unsurvivable, 4-5 foot thick avalanche—especially on very steep, rocky, wind-affected slopes. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    8-12" of low-density snow has fallen in this zone in the past 24 hours, accompanied by light winds blowing out of the SW and then the NW. An additional 4-6" of low-density snow may trickle into the area today. This combination of wind and snow has likely built 1-2' thick wind slabs in upper elevation terrain that gets affected by the wind. This zone is often sheltered from wind and I expect these slabs to be isolated to near ridgelines and exposed terrain features today. While isolated, these slabs will be able to pick up steam as they travel downslope and entrain the several feet of snow that have fallen here in the past week. 

    On very steep slopes, triggering loose snow avalanches (sluffs) is possible. If the sun comes out for long, it won't take long for the snow surface to melt, creating the possibility of natural loose snow avalanches in steep terrain. This problem is fairly simple to manage—if the sun comes out be aware of the terrain you are exposed to from above. Remember that even small slides can have high consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed. 

    ADDITIONAL DISCUSSION:There are two weak layers in the snowpack have been unreactive recently but that continue to be worth paying attention to:

    1. A layer of surface hoar buried 2-3 feet deep. This layer has been unreactive in our recent snowpack tests and has not produced recent avalanches. 
    2. Depth hoar (large-grained weak snow) from December. This weak snow is buried beneath a very dense, 4-5'+ slab. You would have to be unlucky to trigger a slide on this, but its presence has continued to keep me out of the terrain where it is most likely. What type of terrain? Slopes that are very steep, rocky, and wind-affected. The most recent slide we've seen involving this snow failed on exactly such a slope, take a look at this photo.

    Chris found both of these layers in the Cape Horn area on Saturday—he describes them in this video.

    The ongoing snowfall has been accompanied by periods of moderate westerly winds, and you're likely to find fresh wind drifts and slabs along upper elevation ridgelines.

Avalanche Discussion

NEW SNOW AND OLD SNOW

Over the past few days we've seen a slow trickle of snowfall across our region. As this new snow has gradually stacked up, we've enjoyed a significant improvement in skiing and riding conditions. The stiff wind slabs and icy crusts that built during the extended wind event are covered up with soft, fluffy powder and I'm not hearing anybody complain about that. From a snow stability and avalanche danger perspective, we've seen our concerns diverge into two sets of issues that we should be thinking about as we travel in the mountains today:

  1. NEW SNOW: The mountains south and east of Galena Summit have picked up 3-10" of new snow in the past few days, while the mountains to the north and east have stacked 18-24". The winds have been at work at upper elevations, generating a few batches of wind slabs over this period. The freshest batch of slabs will be the most sensitive to triggering today, but older slabs shouldn't be ignored. As you travel down into more wind-sheltered middle and lower elevation terrain you will find better riding and skiing conditions in addition to less dangerous avalanche conditions. That sounds like a good place to be! In areas where more snow has accumulated, you may also encounter some loose snow issues today. Dry loose avalanches (sluffs) will be on the menu in steep terrain. And, if the sun comes out for long, expect to see some natural loose snow avalanches initiating on slopes that are being warmed by the sun. 
  2. OLD SNOW: Everything that is going on in the upper portion of the snowpack is taking place on top of a foundation of weak snow. In our northern areas (Banner Summit and Sawtooths) this weak snow is now buried under a 4-6' thick, very dense slab of snow, which has become difficult to impact with the weight of a skier or rider. Further south, where the slab of snow is thinner, this layer is more accessible and the possibility of triggering a slide on this weak snow is much greater. It is easy to forget about this deeper issue when we are focused on the new snow issues and there is great powder skiing and riding to be had. But, unfortunately we are a long ways from being out of the woods on this one.

The snowpack is complex and tricky this season and in order play in the mountains safely we need to give it the respect that it demands. My primary goal is always to return home safely at the end of the day. After all, I can't go powder skiing tomorrow if I don't make it out safe today. Keep it tight my friends, and enjoy the fresh snow!

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