Boletín de aludes

Olympics

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Avoid wind-loaded features near rocky terrain or convex slopes where you are more likely to trigger an avalanche on Sunday. Small avalanches could grow larger and more consequential if they are able to trigger weak snow grains deep in the snowpack. Uncertainty around these deeper weak layers should make you consider conservative terrain choices.

Problemas de aludes

  • Wind Slabs

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

    Wind loaded terrain will continue to be the most likely location for you to trigger an avalanche in the Olympics Mountains on Sunday. Look for Wind Slabs near rocky features such as gullies and cliffs, on convex rollovers, or on leeward slopes near ridgelines. Slabs may increase in size and reactivity as you ascend in elevation. In some areas, slabs may have multiple density changes from the past few days to fail on. You should use test slopes to check the recent storm snow to see how it reacts to your weight. As you travel, quick hand pits, upslope tests, or visual clues such as textured surfaces, smooth pillow-like piles of snow, or fresh cornices can help give you clues to the distribution and reactivity of wind-affected features to steer around.

    (12/17/2020) Example: Look for fresh pockets of wind-affected snow such as this to steer around on Sunday. The textured surface of the snow in this picture helps indicated it was wind-affected.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    A weak snowpack structure has been identified in the Olympics by professionals and was the culprit for some surprising human triggered avalanches last weekend at Hurricane Ridge. Weak snow sitting atop the Mid-January crust is showing signs of healing, but we are not out of the woods yet. Persistent Slabs do not heal quickly, are difficult to predict, and can break in surprising ways. Surprising avalanches have been easily triggered, propagated widely, and ran quickly, throughout the Olympics and the Cascades since this layer has been buried. Triggering a smaller avalanche in wind-loaded terrain on Sunday could allow a step-down to these persistent layers, creating larger and more dangerous avalanches. If you notice red-flag signs of instability such as shooting cracks or whumpfing collapses as you travel or find persistent grains in your snowpits, put plenty of space between yourself and slopes 30 degrees and steeper.

    (1/30/2021) Human triggered persistent slab avalanche stepping down to 1/13 crust. Estimated to be size D1.5. North facing aspect near Victoria Overlook.

Avalanche Discussion

A natural avalanche cycle this past week in the Olympics was a result of stormy conditions and weak snow grains buried in the snowpack. These grains are sitting atop a stout crust and are driving our Persistent Slab problem. The Mid-January crust/facet combo should be around 35 inches down from the surface and easily identifiable. Weak grains may not exist in all locations, but where they do, we have the 3 elements needed for slab avalanches: a slab, weak layer, and bedsurface. How reactive and widespread this setup is remains a question to be answered, but for now, consider dialing back your terrain choices from what you may normally pursue at Moderate danger. Look for those red flag signs of instability, such as shooting cracks and whumpfing collapses as indicators that you could be dealing with a persistent weak layer. And take some time to dig down to the crust, perform some tests and look for the existence of weak snow grains. If you do not find them, you should not immediately rule out their existence. You should continue to collect more information and ease into terrain. Help us out by letting us know what you find out there by submitting a public observation.

2020-21 Forecast Schedule: Avalanche danger ratings will be issued for the Olympics every Friday through Sunday and during mid-week holidays. During the week when the Hurricane Ridge road is closed, forecast information will be updated daily to include expected conditions and relevant travel advice under the No Rating label.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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