Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

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

Triggering an avalanche large enough to bury you is possible today. This is most likely in areas where the wind has formed drifts and slabs and stiffened the snow surface. Small, loose snow avalanches are possible in steep terrain. These may occur naturally on slopes receiving direct sunshine. Loose snow avalanches that gouge down deeply in the snowpack will become possible during the heat of the day at low and middle elevations.

Conditions are most dangerous where more snow has fallen recently—in the Soldiers, near Dollarhide Summit, and in the upper reaches of the Warm Springs Creek drainage.

Lawinenprobleme

  • Wind Slabs

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

    This zone picked up 6-16" of snow (0.5-1" of SWE) over the past week. Snowfall favored the western portion of this zone, from the Soldiers east into the headwaters of Warm Springs Creek. Periods of moderate winds blowing from a variety of directions have built slabs in exposed terrain. These slabs may be sensitive to your weight today. Yesterday, professionals in the Soldiers triggered a 1-foot thick wind slab with explosives. On Wednesday, a rider was caught and carried in a small slide in the Alturas Lake Creek drainage (report). The avalanche failed in a subtly wind-loaded location, breaking at the interface between the new and old snow. Over the past week, multiple large natural avalanches released in wind-loaded upper elevation terrain of the Sawtooths and Smokys (details on slides here).

    The wind slabs that you'll find today may behave in ways that surprise you. A variety of weak layers exist in the upper 1-2' of the snowpack, and recent wind slabs are resting on top of them. Because of this weak snow, today's slabs may break wider and deeper than you might expect from a "simple" wind slab. Avalanches that break down into these deeper weak layers will be larger and more destructive. This is exactly what happened on Wednesday, when skiers on Titus Ridge near Galena Summit remotely triggered a large avalanche that broke on one of these layers (report with photo and video here). The crown was 2 feet thick and over 500 feet wide and the debris piled up 10+ feet deep against large trees. 

    You can significantly reduce your risk today by steering clear of wind-loaded terrain. As a bonus, you'll also find the best skiing and riding here. Look for signs that the wind has been moving snow, such as ripples and dunes on the snow surface and fresh cornice formation. You'll be most likely to find this in upper elevation terrain, near ridgelines and mid-slope terrain features like ribs and gullies. Slabs may extend down into middle elevation terrain in areas where the wind has been blowing harder. If the snow you are moving through becomes deeper and denser you are likely moving through a wind slab. Snowpack collapsing or cracks shooting out from your skis or sled are clear indicators of an unstable slab.

    ADDITIONAL DISCUSSION: Today will be warm with plenty of sunshine. The dry, new snow that is sitting around will quickly transform under these conditions. Loose snow avalanches will become increasingly likely throughout the day, and the slides will get larger as more snow becomes moist. Avalanches may pick up speed quickly, thanks to the stiff, icy crusts they will be running on. Small loose snow avalanches can be effective triggers for the wind slabs described above. Pay attention to the snow you are moving through and to the terrain you are exposed to from above. 

    You could trigger a wind slab avalanche today. This slide was triggered Wednesday by snowmobilers in the Sawtooth Mtns.

Avalanche Discussion

Avalanche conditions are ripe for getting surprised right now. And not in a good way. Conditions have been changing this week and will continue to do so today. If your last trip in the mountains was last weekend, be prepared to encounter a different snowpack than the one you found then. Read on.

Storms over the past week have gradually piled up 6-16" of snow in this zone. In areas where the wind has been transporting this snow, you'll find wind slabs resting on layers of weak snow. Because of this weak snow underneath, these slabs may display more of a persistent slab character. What does this mean? It means they may be more sensitive and break wider and deeper than you might otherwise expect. This loading process has been slow and incremental, but the weight of the new snow is starting to add up and should not be ignored. 

New snow and wind aren't the only players in the game. Today will be significantly warmer and sunnier than the past week. Late February sunshine will quickly heat up the snow, changing its properties as it does so. The low-density snow will transform, becoming denser and more cohesive. Loose snow avalanches will become increasingly likely on slopes that are receiving direct sunshine, particularly where rocks and trees are helping to heat the snow. The snowpack is significantly faceted in this zone. On lower and middle elevation slopes that face the sun, the entire snowpack is becoming moist on days like today. This can produce loose snow avalanches that gouge down through the entire snowpack, producing larger and more destructive slides. Today's sun and warm temps will also cause the new snow to consolidate and behave more like a slab. On slopes that are teetering at the edge of stability, this additional "slabbiness" may be all that's needed to tip the scales.  

The Avalanche Danger Scale is a tool we use to communicate the conditions you'll find in the backcountry. Each danger rating covers a broad range of conditions. The danger is MODERATE , but we are in the upper end of that category. Today is not a good day to enter avalanche terrain lightly. Spend some time thinking about and looking at the snowpack you are encountering. It's a safe bet that you'll find weak layers in the upper snowpack and a patchwork of wind slabs resting on top. This week's human-triggered and natural avalanches are obvious signs that the snowpack hasn't been adjusting well to this new load. 

With wind slabs on top of weak layers, overlapping loose snow problems, and deeper weak layers in the snowpack, there is a lot of uncertainty today. I'm managing my uncertainty by stepping back from some of the bigger, higher-consequence avalanche terrain that I was comfortable playing in last week. Skiing and riding conditions are excellent right now. Don't let the snow in your face and the warm sunshine lull you into a false sense of security. Triggering an avalanche large enough to bury you is well within the realm of possibility today. 

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