Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Thu
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Out of date — this forecast expired 6 years ago.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

Sunshine and warm temperatures could produce wet loose avalanches. These slides are most likely on very steep slopes that directly face the sun and are sheltered from the wind. Also, skiers triggered soft slab avalanches on very steep, roughly E-facing, upper elevation slopes in recent days. 

Avalanche problems

  • Loose Wet

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

    Another day of warm air temperatures and plenty of direct sunshine will keep natural and human triggered wet snow avalanches on today's menu. There are a few different issues to be on the lookout for—I'll give you the cliff notes here, but you should read the Forecast Discussion section below for a more detailed rundown. Wet avalanche activity involving the newer snow will start on slopes that face E-SE and work its way around through S-SW-W as the sun tracks across the sky. Note how the snow surface is changing. If it's easy to make snowballs, the wet loose problem could be rearing its head. 

    On lower elevation slopes, as air temperatures climb the snowpack will gradually weaken on all aspects of the compass. While this will be most intense on slopes that directly face the sun, shaded lower elevation slopes may also be melting today. If you are falling through crusts into slushy snow underneath, the chance of wet loose avalanches is increasing. Whether you're in shady or sunny terrain, slides will start out small and fan out as they travel downslope and pick up more snow (point-releases). The likelihood of both natural and human triggered slides will increase throughout the day. You can greatly reduce your risk by sticking to colder snow on more shaded slopes or by traveling earlier in the day when the snow surfaces are firm.

    ADDITIONAL DISCUSSION:

    Yesterday, an experienced party intentionally ski cut a small slab avalanche on Copper Mountain (photo below). This slide, and 2 other recent human-triggered avalanches, failed on an east aspect near 9000'. See the Forecast Discussion below for more details. Look for cracks shooting from your skis or board as an indication that you've found a sensitive slab. 

Avalanche Discussion

Today, a trip to the mountains is a little bit like going to the ice cream store; you could get a sample of many avalanche flavors. While the expected avalanche size is fairly small, the variety of avalanches you might see is worth considering:

  • Wet loose - new snow: As expected, the snow that fell since Saturday did not react well to yesterday's intense sunshine. Dozens of small wet loose avalanches released at upper elevations in several mountain ranges within the forecast area. The natural activity peaked in the Sawtooths and was focused on E-SE aspects. Today, this problem will again be most likely in steep, rocky, alpine terrain where more than a few inches of snow fell since Saturday. 
  • Dry loose - new snow: We observed several small, natural sluffs that failed on steep, shady NE-facing alpine slopes yesterday. Many appeared to be triggered by small cornice chunks falling onto the slopes. These sluffs probably won't be large enough to bury people, but they can quickly pick up speed and knock you off your feet or sled and carry you places you don't want to be.  As with the wet loose problem described above, this type of slide is most likely in areas that received more than a few inches of new snow recently. 
  • Soft slabs: In the Banner Summit area and far northern Sawtooths, skiers triggered three small slab avalanches since Sunday. The common threads: SE-E-NE aspects, slopes approaching 40 degrees in steepness, near or above about 9000' in elevation, and about 8-12" of new or windblown snow sitting above a subtle crust with a thin layer of small facets above it. These slides have not been big enough to bury people, but they can definitely push you around.  
  • Wet loose - old snow: At lower and middle elevations, deeper gouging wet loose avalanches are possible as the weak surface ice crusts melt during the day. You're most likely to encounter these on very steep, wind-sheltered slopes where the snowpack is less than about 2 feet deep, especially those with rocks or sparse trees that help add additional heat to the snow. West aspects seem to be most prone to this scenario late in the afternoon. If you can easily push your foot or ski pole through much of the snowpack, or if the tail of your sled or bike drops deeply when you goose the throttle, you have likely found a snowpack where this type of problem is possible. Ben shot a short video north of Ketchum last week that shows these crusts and the weak snow underneath. Monday, I was able to create some large "snow snails" on a low angle slope in the Boulders, an indicator that the entire snowpack was becoming wet and unsupportable. Even narrow full-depth wet loose avalanches are deceivingly powerful.
  • Cornices: Several intense wind events have made up for the overall lack of snowfall this year, and we have some significant cornices built across our forecast area. These huge chunks of snow become increasingly unstable as warm temperatures and direct sunlight causes them to sag and bend. Tuesday, several small cornice chunks that likely formed during the last storm peeled off during the day, triggering dry loose avalanches on the slopes beneath them. Large or small, be alert to the hazard cornices pose if you're traveling below them or on ridgelines. It is very difficult to accurately determine where a ridgeline's "terra firma" stops and the cornice starts; almost every avalanche professional has a story about a close call or accident they've had involving cornices. 

Phew, that's a lot to think about! Fortunately, these problems are fairly easily managed by keeping your eyes peeled and paying attention to the terrain above you. By all means, go out and enjoy the beautiful spring weather. But, anticipate conditions to change over short distances and in short time frames.  

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