Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Avalanche danger is highest in the eastern portion of this zone—the Little Wood Drainage, Mormon Hill, and Swede Peak areas—where significantly more snow fell. Here, avalanches are possible even on sheltered slopes. Snowfall and wind have built slabs in exposed, upper elevation terrain. Additional wind and snow today will help these slabs to grow in thickness and distribution. They may be sensitive to your weight, particularly where they rest on weak surfaces such as facets and crusts. Look for signs of recent wind loading and unstable slabs, such as cracks shooting from your skis or board. Rain on dry snow at lower elevations will increase the threat of loose snow avalanches as the day progresses. 

Lawinenprobleme

  • Persistent Slabs

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

    Snowfall this weekend heavily favored the eastern portion of this zone—the Little Wood Drainage, Mormon Hill, and Swede Peak areas. In this area, over a foot of dense snow fell on a thin and very weak snowpack. Unsurprisingly, the snowpack did not react well to this rapid loading. On Sunday, I spotted numerous large avalanches that had failed in the headwaters of the Little Wood drainage. These slides were breaking hundreds of feet wide, failing at the interface between the new snow and the old snow on slopes that faced away from the sun. In these areas, the long dry spell (basically all of 2020) had significantly weakened the snowpack, leaving a stack of poorly consolidated, faceted snow. Today, you'll be more likely to trigger one of these slides where the wind added snow and helped to build the overlying slab, but they are also possible in sheltered areas.

    Persistent slab avalanches fail in surprising ways and are possible even in areas sheltered from the wind. They may be triggered remotely, from a distance above, below, or to the side of avalanche starting zones. Building in a wide safety margin in your travels is the only way to safely manage this problem. 

    If you are traveling in the Soldier Mountains, where much less snow fell this weekend, refer to the forecast for the Galena Summit and Eastern Mtns to read about the wind slab problem you may encounter.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    Warm air temperatures and rain at lower elevations will increase the hazard of wet loose avalanches today. These slides will be most likely on slopes steeper than about 35 degrees that face NE-N-NW. In these areas, dry snow will become wet for the first time. Slides will start at a point and fan out as they travel downhill. Many slopes at lower elevations aren't steep enough for this type of problem. Unfortunately, quite a few of the ones that are steep enough sit above terrain traps, like gullies and creek bottoms. In these areas, avalanche debris from even a small slide can pile up deeply enough to bury you. This problem will be most dangerous in the eastern portion of this zone, where much more snow fell this weekend.

Avalanche Discussion

The avalanche danger scale is a five-step scale that avalanche forecasters use to communicate information about the avalanche hazards you might encounter in the backcountry. Of course, the world doesn't fit neatly into five boxes. There are innumerable shades of gray and subtleties that can't be perfectly communicated with a simplified scale.  Today, the avalanche danger is MODERATE and human triggered avalanches are possible across our forecast area. However, the type of slide that you might trigger varies significantly. Let's take a quick look:

  • Pioneer Mountains and Little Wood drainage: The southeastern corner of our forecast area got clipped by a significant stream of water this weekend. While many of our other areas picked up just a few inches of snow, The Swede Peak SNOTEL recorded 15 inches of snow and 1.3 inches of SWE (snow water equivalent). Here, a very weak snowpack was stressed with a significant load for the first time this season and numerous large, natural persistent slab avalanches occurred. These types of slides can be triggered remotely, including from the bottom of an avalanche path. Dealing with this problem involves building wide safety margins into your travel plans.
  • Sawtooth, Smoky, White Cloud, and Boulder Mountains: 2-6 inches of snow fell in these mountains this weekend, and a few more will fall today. The wind built small slabs out of this new snow in upper elevation terrain exposed to the wind. 

Think about how differently your travel practices need to be to manage these problems. A "simple" wind slab problem creates hazards that are somewhat predictable and avoidable. If you choose to enter avalanche terrain with this type of problem you know what to look for and avoid (steep, wind-loaded slopes). However, a persistent slab problem is a different beast entirely. If you are trying to avoid the hazard posed by one of these beasts you need to look at a significant chunk of terrain as being "off-limits". In both cases, triggering an avalanche is possible, but the type of slide and the way you deal with the hazard are very different.

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