Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Tue
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Expect wind-effect to be significant on Monday with slabs on a variety of features. Ease into terrain slowly as you take stock of how the storm impacted the zone. Look for red-flag signs of instability such as shooting cracks, whumpfing collapses, recent avalanches, or hollow feeling snow as indicators to avoid slopes over 35 degrees.

Problemas de aludes

  • Wind Slabs

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

    Strong to extreme winds have impacted the zone, certainly transporting snow and forming Wind Slabs. Slabs will be larger and more widespread as you ascend in elevation and will be most likely on leeward slopes at ridgecrest or near rocky features such as cliffs and gullies. Fresh cornices have also surely been built by the wind and will be sensitive to human triggers, but can be used as a visual clue to help you identify wind-loaded slopes. Other clues such as textured surfaces or smooth pillow-like piles of snow can help you identify wind-loaded slopes to avoid. At lower elevations, Wind Slabs could be complemented by pockets of reactive snow in wind-sheltered areas behaving more like Storm Slabs. Whatever avalanche character you tend to give the new storm snow, avalanches will be more likely on slopes over 35 degrees, near rocks, or on convexities. Uptrack tests or hand pits in non-consequential terrain can help you determine slab potential and some clues to bonding, but you shouldn’t be performing these tests on slopes that may be wind-loaded. A better plan is to use test slopes to see how the recent snow has bonded to the previous snow surface and how it is reacting to your weight. If you find a poor bond or suspect wind-loading avoid slopes over 35 degrees.

    (11/25/2020) Test slopes can give you a lot of good information about how new snow has set-up after or during a storm. Earlier this season, this test slope showed that slabs were sensitive and propagating easily.

Avalanche Discussion

NWAC’s weather station at the top of Alpental has recorded maximum gusts over 50mph for all the daylight hours on Sunday, with a high of 95mph as of 6:00 pm. Wind speed averages have been much lower throughout the day, but on an upward trend, reaching the 40s. This storm was definitely more winterlike than springlike, and as the snow continues to pile up, winds should taper, but remain strong into Monday. Observations from professionals on Sunday indicate that the new snow is not bonding well to the prior snow surface, particularly in areas where a melt-freeze crust existed, which is almost everywhere except northerly aspects at upper elevations. This could lead to sensitive conditions on Monday in all areas, not just the ones where the wind has drifted the snow into thicker slabs. Avalanches have the ability to run far and fast on this crust as slabs, loose, or even wet if the sun comes out and destabilizes the newly fallen snow. Wet avalanches may be more likely in the eastern part of the zone where the chance for sun breaks is higher. We expect you will find a mix of wind-stripped surfaces, wind slab, and poorly bonded storm snow on Monday, with all avalanches confined to the new snow above the 3/28 interface. 

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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