Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

You will likely receive no warning signs before triggering a 2-4' thick avalanche involving dense slabs of snow. A very large natural avalanche failed two days ago on Galena Peak and triggering similar slides is likely today. Smaller avalanches near the surface of the snowpack will be easy to trigger especially in terrain exposed to the wind. These slides can increase in size, especially in large terrain, and can move the entire snowpack downhill. 

Lawinenprobleme

  • Persistent Slabs

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

    A very large natural avalanche failed on Galena Peak sometime between Friday night and Saturday morning. The crown spanned 2,000 feet of terrain and the slide ran over 1,000 vertical feet. The photo at right/above shows a large slide that was triggered by the Sun Valley Ski Patrol earlier this week. These are the types of avalanches that you are likely to trigger today.

    Under the recent storm snow, you will find thick, very dense slabs sitting on layers of very weak snow. Watch this video to get a sense of just how dense these slabs are. If you dig down, you'll find thick piles of facets with or without surface hoar on shaded aspects, and crust+facet combinations on slopes that get more sun. You can trigger avalanches that fail on this weak snow from long distances away. Any avalanche that fails on this weak layer will be large and destructive. 

    Because the slabs on top of this weak layer are so dense, you aren't likely to encounter many or any signs of instability before triggering a large, potentially unsurvivable avalanche. As a local professional wrote in their observation on Friday, "stability felt good, until you dug into the snowpack..." Keep this weak snow at the front of your mind when you are moving through the mountains. The only guaranteed way to avoid this problem is to steer clear of avalanche terrain and slopes threatened by overhead hazards. 

    (2/6/2024) The Sun Valley Ski Patrol ski-triggered this large avalanche Tuesday morning in the Cold Springs Chutes in the Sunrise Expansion Area. This area has not yet been opened to the public. It failed on a NE aspect near 8000'. The slide was 2-4 ft tall, 100 ft wide, and broke branches during its 900 ft vertical run. The debris piled up 4-7 feet deep against trees. Photo: Sun Valley Ski Patrol

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Recent storms brought several feet of fresh snow to this zone. Expect to encounter a range of issues related to this new snow:

    Wind slabs: Our weather station on Peak 2 in the Soldiers reports northerly winds blowing at loading speeds since yesterday afternoon. Winds on top of Baldy have been lighter. There was plenty of loose snow to move around when the winds started blowing. Look for drifts, ripples, and dunes on the snow surface as indicators that the wind has been at work, and expect fresh wind slabs to be sensitive to your weight. These slabs are likely to be stiff and dense where winds have been stronger.   Cracking in fresh slabs is a sure sign of instability. These slabs can produce slides large enough to bury you. 

    Loose snow: Sluffs of new snow will be easy to trigger on steep slopes without crusts or wind slabs at the surface. Natural loose snow slides may occur on slopes that face the sun if the clouds allow more sun through than expected. If the snow you are traveling through is becoming moist and you are seeing balls of wet snow rolling downslope, these small slides may be releasing naturally. Slides that entrain moist/damp/wet snow can quickly become larger and more powerful than you might expect.

    Slabs at new/old interface: Snowpit observations and natural avalanches point to the potential for avalanches failing at the base of the new snow, even in terrain sheltered from the wind. Our observations are limited, and we can't yet say with confidence if this interface will be a longer-lived weak layer or just a flash-in-the-pan. Some of the observed avalanches that failed on this layer in neighboring zones broke many hundreds of feet wide. 

    Even small slides can knock you off your feet and send you for a ride in ugly terrain. Surficial slides will travel fast and far on the stiff surfaces underneath. Remember that all of these smaller avalanches take place on the stage set by the Persistent Slab problem above. Smaller slides can be effective triggers for much larger Persistent Slab avalanches as they rocket downslope. 

Avalanche Discussion

Our snowpack currently has two contrasting parts that are equally important to keep in mind heading into the hills: the new snow that is providing excellent skiing and riding, and the weak snow that lingers underneath. If you've ever walked or ridden along a ridgeline at sunset, you know what it means to walk the line between the sunshine and the shadows. Like in life, we like to operate in the sunshine. Shadows however do not make the sun any less bright. Seeing both turns up the contrast and allows us to see more of the world. Heading into the mountains today, it will be easy to be tricked into just ignoring the weak snow that lays beneath the high-quality, soft powder. Seeing the whole picture will allow you to make better decisions and come home safely. 

The sunshine is the new snow that fell from our recent storms. Providing high-quality riding and skiing, this is what you have had blow into your face on your way downhill lately. It lays on top of a supportable melt-freeze crust (2/1). With past sustained moderate to strong winds that shifted from the SE to NW, this snow formed wind slabs in most exposed middle to upper elevation terrain and led to a small solar-initiated dry loose cycle with our first dose of sunshine a couple of days back. These issues are at their worst in our Galena and Eastern Mtns and Soldier and Wood River Valley Mtns zones where more snow fell. While these wind slabs and new snow still linger at the new/old snow interface, managing surficial problems is approachable. Without any cracking or collapsing in Eagle Creek to warn me of a deeper issue, silky slopes doused in golden light appeared inviting. Looking back over the opposite side of a ridge at sunset, I unexpectedly spotted a very large avalanche staring back at me, almost hidden in the shadows.... (see photo)

The shadowsare what lay below. Underneath the new snow is a series of weak layers that will not provide much if any warning before releasing a large avalanche. Ten days of snowfall created a thick, meaty slab on top of a series of profoundly fragile weak layers. This slab shielding the weak snow is dense and firm, and will be hard to punch through on your machine or with your ski pole. This makes warning signs like cracking and collapsing unlikely, but don't let this fool you. This weak snow near the base of the snowpack has produced many large to very large avalanches in recent days — including a slide that tore across the entire NW bowl of Galena Peak. This problem is at its worst in our southern two zones where the weak layer is not as deep. As we head further north towards Banner Summit, the snowpack gets deeper the the likelihood of impacting this weak snow to produce a slide gradually decreases to possible. 

It can be hard to remind ourselves that the likely possibility of triggering a large destructive avalanche remains when there is soft snow on untracked steep faces. Today, remember that there is plenty of soft snow to be found on lower angle slopes. While the decrease in warning signs can nudge us to get caught up in dreams of steeper terrain, remember that shadows still lie below. Make a plan with your partners before heading into the hills and stick with it despite temptations in the moment. It's been a full season of this similar message, but I'll continue to say it: our goal today is to walk back in that door tonight and see another sunset tomorrow. 

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