Avalanche forecast

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Buried weak layers 2-4 feet deep in the snowpack continue to pose a significant hazard. Wind slabs that formed during last week’s storms added stress to these layers, and pose a hazard in their own right. An increase in wind speeds this afternoon may create thin and touchy fresh wind slabs. You’re most likely to encounter both of these problems in steep and rocky upper elevation terrain.

Avalanche problems

  • Persistent Slabs

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

    This zone has been plagued by persistent slab problems all year long. There has been just enough snowfall here to build a hefty slab of snow on top of our early season weak layers, but not enough to really put these layers “to bed”. Since they remain close to the surface, the likelihood of triggering an avalanche on this weak snow is higher. Last week, in the northern portion of this zone, I watched as a group of riders remotely collapsed a large alpine bowl from well below the starting zone. The next day, a large avalanche occurred on a nearby slope, wiping out the majority of the season’s snowfall (photo at right). In the Boulders, a significant wind event one week ago was able to set off several large persistent slab avalanches.

    As the days pass without significant loading and the snowpack gets a chance to take a breather, the places where you might be able to trigger a persistent slab avalanche become fewer and further between. However, last week’s avalanches in the White Clouds and the Boulders, unstable snowpack test scores, and continued reports of collapsing in the snowpack let us know that this problem can’t be written off. Today, you’ll be most likely to encounter this problem in similar terrain as in the photo at right. That is, steep, rocky, and heavily wind-loaded.

  • Wind Slabs

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

    4-8” of snow fell in this zone during the trickle of storms last week. Throughout these storms, moderate to strong winds blew from a variety of directions, creating a patchwork of wind slabs in upper elevation terrain. During the final day of snowfall (Saturday), wind speeds dropped dramatically, leaving a thin blanket of low density snow on top of these slabs.

    Sunday night, wind speeds picked up a bit, transporting some of the snow that fell at the end of the storm. This afternoon, wind speeds are expected to increase again, which may result in another round of slab building. These slabs are likely to be a bit touchier than the older generations of slabs, but they will likely be relatively small. Older, stiffer slabs underneath will be less sensitive to your weight, but the resulting slides will be larger (photo at right). Expect to find these slabs in upper elevation terrain, near features that slow the wind down and force it to drop the load that it is carrying.

Avalanche Discussion

If you are a regular reader of the forecast, I’d imagine that you are getting tired of hearing about persistent slab problems. Unfortunately, we’ve been dealing with them all season and it is my job to talk to you about them. But, as we know, variety is the spice of life and I’ve got a bit of extra spice for you this morning. Drumroll please...a new persistent weak layer!

This layer isn’t buried in the snowpack yet, it is currently sitting on the surface. Cold, clear nights and days create conditions that are conducive to the formation of faceted snow grains, or facets for short. We call them facets because they have sharp, angular edges on them, much like a cut gemstone. Facets are problematic because they don’t bond well to the snow around them, which makes them a “great” weak layer. Transforming new snow into facets is a process that can take place quite quickly, but rounding (the process by which facets gain strength) takes place much more slowly. And there you have it, a weak layer of snow that will persist for some time.

It's much easier to look for faceted grains in the snowpack before they get buried. If you’re out and about before the storm this weekend, spend some time looking at the snow that is sitting on the surface and see if you can see identify some differences between it and freshly fallen snow. If you look hard can you still see recognizable snowflakes? Can you make a snowball out of it? Does it feel different on sunny aspects than shady aspects? Try to map out the distribution of facets at the surface and then watch how different areas behave as they get loaded.

In our northern areas, where significantly more snow fell last week, a weak layer of these facets may have already been buried. Yesterday, I was able to spot an avalanche on Copper Mountain that had the character of a persistent slab avalanche. Read the problem discussion for the Banner Summit zone for a bit more information. This avalanche failed well below the ridgeline where wind loading would be most intense, indicating that wind loading wasn’t likely the primary factor in its release. Whether or not this is a widespread problem or not is yet to be determined.

Regions covered