Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

Sun
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 7 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Triggering a dangerous avalanche remains likely, especially on slopes with wind-stiffened or drifted snow. Although buried weak layers are improving, lingering signs of instability indicate we're not out of the woods yet. Choosing lower-angled, conservative terrain continues to be the best approach.

Problemas de aludes

  • Persistent Slabs

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

    Regular readers of the forecast have heard plenty about the layer of surface hoar buried 1-2 feet deep throughout our area (read more about it in the Discussion below). It was responsible for a large number of human-triggered avalanches last weekend. At that point, the seriousness of the situation was clear: large, rumbling collapses were commonplace, and, of course, people were triggering avalanches.

    In some ways, conditions are more dangerous now. As obvious signs of instability become less frequent and test scores improve, it's easy to gain false confidence. Observers on Banner Summit yesterday reported a few large collapses, especially in wind-affected terrain. This zone also received more new snow Thursday night, which added a bit more load to the buried weak layer. Continuing to choose lower-angled terrain remains the best way to manage this lingering instability.

    Additional Discussion:Winds increased yesterday and overnight, and there may be small, fresh wind slabs today in exposed terrain. These may be sensitive on their own, but are also adding weight to the buried weak layer described above. 

Avalanche Discussion

In last Wednesday's Digging Deeper talk about Understanding Weak Layers, we discussed how to tell when buried weak layers have improved. Did I provide a clear answer? No, because there isn't one. In the life cycle of a persistent slab problem, this is the most dreaded time. Signs of instability begin to wane, and the desire to break out of the mellow terrain you've been playing in begins to weigh heavily on your decision making. From a pure stability standpoint, conditions were more dangerous last weekend. But if you throw humans into the mix, I'd argue it's more dangerous right now.

While our area is known for some wicked facet layers, a widespread surface hoar layer isn't particularly common. Sure we get them occasionally, but they tend to be more "pockety" in nature and rarely produce such impressive avalanche activity as the one we have now. Surface hoar can be extra tricky—in fact, some studies have shown that it's the weak layer that produces the most avalanches that catch professionals. 

So how do you tell if a buried weak layer's improved? In the Digging Deeper talk, I said the key factor was time. Time since the last loading event (snowfall or wind), and time since the last sign of instability, and then a bit more time. With moderate to strong winds in the forecast today, and a few significant signs of instability still being reported, I don't believe we're there yet. So my advice is this: be patient. Even if you think conditions are getting better, what harm is there in giving it a little bit more time?

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