Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

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. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    This zone picked up 14-18" of snow (1" of SWE) over the past week. 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. On Wednesday, a rider was caught and carried in a small slide in the Alturas Lake Creek drainage (photo above/right, 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. On Wednesday, 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. 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. 

    A snowmobiler was caught and carried in this small wind slab avalanche in the Alturas Lake Ck Drainage of the Sawtooth Mountains. They were not buried or injured. The slide released on a N-facing slope at about 9,100'.

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 14-18"+ 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. In favorable terrain, like the steep, craggy terrain of the Sawtooths, these slides may entrain a lot of snow, producing larger avalanches. 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 and overlapping loose snow problems, 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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