Boletín de aludes

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Conditions will become dangerous as the sun and warm temperatures turn the snow to mush. The likelihood of both natural and human-triggered wet avalanches will increase. Plan an early start, and be ready to move to gentler or colder terrain as the surface crust breaks down. There is a small chance of triggering a dry slab avalanche on very steep, shady slopes at middle and upper elevations.

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    The threat of natural and human-triggered wet avalanches will quickly increase as the day heats up. Last night's temps were extremely warm, and there was at least some cloud cover. This means the surface freeze could be thinner/weaker this morning than in past days. While the sunshine will be muted by high clouds, today's temps may be the warmest yet. It's likely that conditions will deteriorate more rapidly today, and there is a possibility that wet slides could be larger.

    While wet slide conditions are fairly predictable, the expected nature (type, frequency, and size) of the avalanches can be hard to pin down (see Forecast Discussion below). With the exception of one large wet slab, most natural wet avalanches have been relatively small. However, the extended heatwave continues to pump liquid water into the snowpack. Will the cumulative effects of the prolonged warming lead to an uptick in the size and frequency of avalanches? That's hard to say. But I don't recommend overstaying your welcome in steep, sunny terrain to find out.

    If you head out today, the first order of business will be evaluating the overnight freeze. How thick is the crust? Can you punch your foot or ski pole through it? The thinner it is, the less time you'll have to ski or ride. Plan your day accordingly—start early, and plan to be off and out from beneath very steep, sunny slopes before the crust completely thaws. Once you're punching through the surface, it's time to be out of harm's way.

    (3/24/2022) Wet loose avalanches in the northern Sawtooths.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1–2

    Triggering a dry, persistent slab avalanche has become unlikely—but not impossible. The last triggered slides were over a week ago (photo), but the weak layers responsible for these avalanches still exist in middle and upper elevation shady terrain. Where is there still a small chance of triggering a persistent slab avalanche? On shadier, very steep (over about 35 degrees) slopes where past wind events have built a stiffer, denser slab. While less likely, triggering slabs in sheltered terrain can't be entirely ruled out.

Avalanche Discussion

WET AVALANCHES: THE NATURE OF THE BEAST

It's Day 5 of an extended warmup. While wet avalanche conditions are predictable, the expected type and size of wet slides are not. Here are some of the beasts that could rear their ugly heads as the heatwave continues:

Thin Wet Loose Slides: These are your common, "run of the mill" type of wet snow avalanche. While they are typically small (photo), they can sweep you off of your feet and carry you where you don't want to go. They often originate near warm cliff bands and rocks on very steep slopes that directly face the sun. We've observed dozens of these slides in the past few days across all forecast zones. 

Gouging Wet Loose Slides: As the heatwave continues to increase the buildup of liquid water in the snowpack, wet avalanches can become larger and deeper. Thin wet slides that begin on the surface can gouge down deeper into soupy, saturated snow. These slides are more likely where the snowpack is shallow and weak (less than about 2 feet thick), and on very steep, rocky slopes that are sheltered from the wind.

Wet Slabs: Ben spotted a wet slab avalanche on Thursday on an E/SE-facing slope at 9,700' in the Boulder Mtns. It was a large, destructive slide that broke over 300' wide (photo). Wet slabs occur when meltwater pools and spreads along a weak layer in the snowpack, weakening the bond of the overlying slab. These slides are notoriously difficult to predict. We do know that to have a wet slab, we need defined weak layers of snow and plenty of meltwater production. As it turns out, we have both of these!

Cornices: Large cornices sit atop many steep, alpine ridgelines (photo). Cornice failures are likely in the next few days as warm temperatures cause these features to sag and break. Give cornices a wide berth and limit the time you spend below them. 

The silver lining is that these differing wet avalanches can all be avoided with the same tactics: Plan to start and end your day early. Pay attention to the extent of the overnight freeze—if the snowpack isn't supportable to start, pull the plug. Monitor how quickly the surface crust breaks down, and be ready to move to colder or gentler terrain at the first hint of punching through the crust. And make sure you plan a safe exit to your day, one that's not threatened from above.

Catch up on what happened this past week in Ethan's latest Weekend Update!

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