Lawinenlagebericht

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Kernpunkte

Avalanches releasing on weak layers buried 2-4 feet deep remain a possibility on very steep, rocky, wind-affected slopes at upper elevations. This problem will be most prevalent in the alpine terrain of the Boulder, White Cloud, and Pioneer Mountains. Recent snowfall and moderate winds formed wind drifts at upper elevations which will be small but may be triggered by the weight of a skier or rider. This problem is most likely in upper elevation terrain of the White Cloud Mountains, where the most snow fell.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    This winter got off to a strong, early start and then stalled out. Unfortunately, as is so often the case, the remnants of the early season snow generated a weak base for our snowpack in this zone. Without recent, significant loading events, the likelihood of triggering an avalanche on this weak snow is slowly decreasing, but the possibility remains. On Sunday, a frequent observer reported that the combination of "thin snow cover, history of shallow/weak snowpack, and hard wind slabs" kept him and his partners out of rocky, upper elevation terrain in the White Cloud Mountains. On Friday, I went for a recreational ski day in the Lost River Range. These mountains are the next range to the east of this zone and are outside of our forecast area. However, the snowpack there isn't entirely different. From a safe ridgeline, I was able to remotely trigger a very large avalanche that failed near the ground on similar weak snow that fell in September and October. Click on the link to see photos and read a few more details.

    While triggering a persistent slab avalanche is generally unlikely, it remains possible in terrain with 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 lots of thin spots on the snowpack where weak layers are closer to the surface.

    Read more about why these slopes are particularly hazardous in the Forecast Discussion below.

    ADDITIONAL DISCUSSIONYesterday's storm brought 4" of snow to the White Cloud Mountains, which make up the northern portion of this zone. If you are traveling in this portion of the zone, refer to the wind slab Problem Discussion for the Sawtooth & Western Smoky Mtns.

Avalanche Discussion

The winter of the haves and the have nots continues. If you frequently ski or ride in this zone, you know that you are in the latter category. The recent storm brought 4" of snow to the White Clouds, 1" to the Boulders and the Galena Summit area, and nothing at all to the Pioneers.  This pattern has been present for much of the winter and has "helped" to generate the ongoing persistent slab problem that we're stuck with. For weeks we've been warning you about the sort of terrain where you are likely to encounter this sort of problem: steep, wind-affected, and alpine. Let's take a minute to look at why these sorts of areas are more problematic.

  • Steep: As a slope gets steeper, gravity is pulling down more intensely on the slab. Slopes in the 35-45 degree range are at the sweet spot, where it isn't so steep that the snow just sluffs off, but it is steep enough for gravity to have an appreciable downward force on the snowpack. 
  • Wind-affected: The wind plays two roles to increase the likelihood of triggering slides. In areas that are more commonly scoured, the snowpack is thinner and the weak layers are closer to the surface and easier to impact. In areas that are loaded, a stiff, dense slab of snow is stressing the weak snow underneath. Oftentimes these areas exist right next to each other, creating a scenario where likely trigger points are adjacent to meaty slabs. Not good.
  • Alpine flavor: Upper elevation terrain is typically steeper and more wind-affected than terrain lower on the mountain. In addition, this sort of terrain commonly has lots of scree piles, rocky ribs, and cliff bands. These features help to create lots of thin spots on the snowpack where weak layers are closer to the surface and easier to impact.

Spend some time scrolling through our media gallery and look at some of the deeper avalanches that we've been seeing this season. Try to identify these characteristics on slopes that have already avalanched. Then, as you are out in the backcountry, see if you can find slopes that have similar characteristics that haven't avalanched. These are exactly the types of slopes where you are most likely to encounter this problem today. The likelihood of encountering this problem isn't high, but the consequences sure are. 

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