Avalanche forecast

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Avalanche danger

Tue
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Out of date — this forecast expired 7 years ago.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

Triggering an avalanche on weak snow near the ground remains a possibility on very steep, rocky, wind-affected slopes. You'll be most likely to encounter this problem at upper elevations in the White Cloud and Boulder Mountains. The combination of 1-3" of new snow and wind is building isolated wind slabs in exposed terrain. These slabs are likely to be small, but touchy, thanks to the faceted surfaces they are being deposited on. At middle and lower elevations, and on more wind-sheltered slopes, the snowpack is generally stable and avalanches are unlikely.

Avalanche problems

  • Persistent Slabs

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

    The remnants of early-season snowfall make up the base of the snowpack in much of this zone. In the White Cloud Mountains, which received the most snow during December and January, this base is supporting a meaty 3-4' thick slab of snow (video at right). As you travel south into the Boulder and then the Pioneer Mountains, the slab thins because less snow has fallen (recent video from Pioneers here). Thanks to a lack of recent loading, triggering a large avalanche involving this weak snow has become unlikely, but I'm still not ready to write it off in my personal decision-making and I'd recommend you do the same. Slopes where you are most likely to encounter this problem have the following characteristics:

    • Steep: Slopes in prime-time avalanche terrain around 35-45 degrees.
    • Wind-affected: Heavily wind-loaded by past or recent wind events.
    • Alpine flavor: Complex terrain with scree piles, rocky ribs, and cliff bands help to create thin snow cover where weak layers are closer to the surface.

    ADDITIONAL DISCUSSION1-3" of snow fell in this zone overnight, accompanied by moderate to strong winds out of the W-NW. Without a lot of ammunition for the winds, any slabs that are forming should remain small and isolated, but these slabs may be touchy due to the weak, faceted snow surfaces they were deposited on. While small, encountering one of these slabs in very steep and rocky terrain could have high consequences. 

    Read a bit more about crusts, facets, and wind slabs in the Forecast Discussion section below.

Avalanche Discussion

Let's spend a minute thinking about crusts, facets, and the way the wind transports the snow:

CRUSTS:Crusts in the snowpack form when dry snow is melted and then frozen again. The most common ways these crusts form are with warm air temperatures, direct solar input, or rain. Crusts are often associated with faceted snow grains, which are described below. The combination of crusts and facets commonly form weak interfaces in the snowpack.

FACETS:Snow grains are in a constant state of change. Even before they hit the ground the structure of these crystals is rearranging in order to satisfy the whims of the laws of physics. Under weak gradients (the change in a given property over a certain distance), snow trends towards a more rounded state. Rounded grains tend to pack nicely with each other and form strong bonds. However, when placed under strong gradients, snow trends to a more angular state (facets). Cold, clear nights and days, like the ones we saw last week, 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. This is a significant simplification of the processes involved here, but I hope it helps you grasp the basic points.

WIND:When the wind is sufficiently strong, it picks up snow and transports it to another location. While the snow particles blow through the air or bounce along the snow surface, they break up and become smaller. The smaller grains pack well into drifts once they're deposited. And just like that, you've got a wind slab. The speed of the wind plays a critical role in this process. Steady, moderate winds are great at building widespread, thick slabs. But shifting, variable, gusty winds don't do nearly as good of a job. If the wind doesn't blow hard enough it can't pick up much snow, but if it is blowing too hard it will throw the snow up into the air where it sublimates, never to rejoin the snowpack. The winds blowing yesterday and last night have been more on the gusty, and strong end of this spectrum. 

Keep these two patterns in mind — an overlapping patchwork of crusts, facets, and wind slabs. Today, triggering a wind slab is most likely where the presence of a crust+facet combination coincides with a fresh wind slab. Because of this, the problem will be isolated to specific terrain. In many areas, you won't find any touchy wind slabs. But in the right terrain, you will. Be alert to this as you travel through the backcountry today, and don't let the lack of touchy slabs in one location lead you to believe that this problem doesn't exist anywhere.

Regions covered