Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Tue
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Very large avalanches were remotely-triggered by skiers in this zone on each of the last three days. Triggering similar slides will be increasingly likely on many slopes today as more snow falls. Avalanches can be triggered from long distances away from steeper slopes and can run into gentler terrain below. Panels of wind-drifted snow will be reactive to your body weight. These smaller natural and triggered slides can step down to the weak layers beneath, creating much larger, more destructive avalanches. 

We have issued an AVALANCHE WATCH for this zone. Avalanche danger will increase significantly overnight as an intense storm impacts the region. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    Multiple large to very large persistent slab avalanches were remotely triggered in the Galena Summit and Eastern Mtns and Soldier and Wood River Valley zones each of the past three days (photo at right/above, video here). Slides occurred above Trail Creek, the East Fork of the Big Wood River, and near Baker Creek. These avalanches failed as dense, 2-3 foot thick slabs of snow. The culprit weak layer in these slides was the impressively widespread and fragile snow that developed during the December drought. Dig down and you'll find facets and/or surface hoar on shadier aspects and crust + facet combinations on sunnier slopes. 

    Triggering similar slides is more likely again today as we add more stress to the snowpack throughout the day. You can trigger avalanches that fail on these weak layers from long distances away from steeper slopes. Some of the triggered slides from the past three days released over 1,000' away. Pay attention to the terrain you are in, exposed to from above, and the presence of nearby parties. 

    The snowpack was touchy after it's first loading event a few days ago — and now we're just adding to the stress on those same weak layers. The recent triggered slides clearly indicate that the snowpack is not reacting well to this loading. Pay attention to the terrain you are in and the terrain you are exposed to from above. 

    This large remotely-triggered persistent slab avalanche on a NE slope at 9400' above the East Fork of the Big Wood broke 250 feet wide and ran over 1000' downslope.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–2

    Overnight we saw sustained strong winds that brought with them up to 4 inches of snow. This fell in addition to the over a foot of light snow that was already available for transport at upper elevations from our last storm. Wind drifted this snow into sensitive slabs both at upper and exposed middle elevation terrain. Expect these pockets to be reactive to your body weight and larger as you climb higher in elevation. As wind and snowfall continue throughout the day, expect the size and reactivity of these slabs to increase. 

    Importantly, these smaller slides can trigger much larger, much more dangerous avalanches on the persistent weak layer described above. Keep an eye out for rippled surfaces, hollow-sounding stiff snow, and cracking shooting out from your skis. The low-density snowfall will mask the presence of these slabs. Avoid drifts, dunes, and pillows.

Avalanche Discussion

The mountains didn't need any more snow or wind to get touchy and scary, but they're getting it anyway. Dangerous avalanche conditions only got worse overnight as sustained strong winds brought in 1-4 inches of snow, and will rise throughout the day as up to 13 inches of snow falls in areas of this zone like the Pioneers. This snow will build our slab to 2.5-4 feet thick in this zone, laying on top of an already stressed and impressively fragile widespread layer of weak snow. In each of the past three days, large to very large avalanches were remotely triggered near the boundary of the Galena Summit and Eastern Mtns and Soldier and Wood River Valley Mtns zones. Near Johnstone Peak two days ago, I was able to trigger a slide from nearly half a mile away that spanned multiple alpine bowls and moved the entire snowpack downhill. Slides like these will be more likely today, with the chances of triggering them increasing throughout the day as the snow falls and wind blows. The wind will build smaller but still consequential and reactive slabs at upper and exposed mid-elevations that are likely to step down to create larger avalanches if triggered.

Not only do we have a slab on top of a widespread weak layer, but the slab has become increasingly hefty and dense. The consequences of this are two-fold: and increased force and consequence of slides, and a decrease in warning signs to before triggering them. To put the power and scale of these slides into perspective,  the force of one of the dense slabs that failed about Trail Ck created when moving downhill triggered another large avalanche in unconnected terrain just from the impacts of the snow on the hillside. In areas where the snowpack has remained thinner (southern and eastern mountains) the slab is a bit thinner and triggering avalanches on it will be slightly easier. Across our region, any avalanche you trigger that involves this weak snow is likely to break hundreds of feet wide (or wider) and will send a majority of the snowpack rocketing downslope. Triggering one of these slides is likely today.

Yesterday was dangerous. Today is worse. Riding out up the drainage or starting up the skintrack, remind yourself that avalanches large enough to damage a house are likely. These slides can fail in places that you haven't seen them before and can pull back into lower angle terrain above steeper slopes. Avalanches can be triggered from large distances away, and can not only impact your group but also others around you. Heading into the mountains today, there are two ways your day in the backcountry could go: low angle powder skiing and riding, wiggling in safety with friends before coming home safely at the end of the day — or the alternative. 

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