Boletín de aludes

West Slopes North

Northwest Avalanche Center
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Peligro de aludes

Mon
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

Another 6 inches or so of snow will fall over the 6 inches that fell Saturday, and it is likely that you could trigger avalanches in the storm snow layers. They will be easiest to trigger in wind-loaded areas, such as along ridgelines and leeward slopes, in gullies, and around rocky outcroppings. Avoid steep slopes on Sunday, especially where you notice thicker deposits of wind-drifted snow.

Problemas de aludes

  • Storm Slabs

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

    Human-triggered avalanches are likely on Sunday. Most avalanches will fail within the new snow that fell in the last 24 hours, around a foot in depth. It could be the case that only shallower pockets will release, or thicker wind drifted pockets could release as well. Check out THIS observation from Saturday near Heather Meadows, where cracking and simple weaknesses were observed in the new snow, good indicators to stay off nearby steep slopes. The storm was accompanied by wind, so depending on your location, you may encounter large drifts of thicker snow. Expect the wind-affected areas to be more reactive to a human trigger.  This is especially the case along ridgelines, on leeward slopes, and around rocky outcroppings. The highest chances of triggering large avalanches are on large, unsupported features in wind-affected terrain. 

    During your travels pay attention to variations in snow surface conditions- is the surface light and fluffy, or does it feel firmer as you slightly shifted your location? Pay attention to obvious clues such as cracking. If you’re ski/split touring, this is a great day for doing skin-track tests (see media). Although you’re constantly assessing the snowpack as you travel, unless you have experience with snowpack checks and tests, stay off slopes steeper than 35 degrees on Sunday.

    (2/19/2022) Human triggered shallow slabs failing within the new snow layer occurred Saturday afternoon in the Baker backcountry. Expect to encounter deeper ones on Sunday. Photo: Pete-Durr, USFS Backcountry Ranger

  • Persistent Slabs

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

    Lingering concerns with the persistent weak layer exist as more snow loads on top. Although an avalanche hasn’t been reported on this layer in over a week, nearly two feet of new snow (weight) on top could tip the scales and we might see avalanches on this layer again. The layer exists around 2 feet below the old snow surface on upper elevation northerly aspects. Add this problem into the equation, and traveling out in these areas on steep terrain with additional new snow is not a good idea on Sunday.

    (2/12/2022)

    Large (D2) natural slab avalanche on a north aspect of Table Mt at ~5500'. This is suspected to have released in the late January crust-facet layering.  Another foot+ of snow on top could mean more avalanches might occur on this layer. 

    Photo: Lee Lazzara

Avalanche Discussion

Sunday is a good day to keep bullseye clues, or red flags, in the forefront of your mind. These are the best indicators of when to avoid some or all avalanche terrain. One red flag which is already in the cards for tomorrow is recent snowfall. Wind is also a factor. Look out for recent signs of avalanches and unstable snow. Any one of these indicators means there’s probably an increased chance that you’ll encounter avalanches. If you’re traveling to steeper areas, make sure you’ve done your research by using small test slopes, investigated layer bonding, and determined wind slab potential for starters, before heading out onto the slope.  Have a think about the underlying snow surface as well. May old surfaces are smooth and slick. The new snow may not stick well to the old surface in some areas. 

The return to winter means big changes from the last few weeks. Change your mindset as a result of this, as the avalanche problem, likelihood, and size shifted dramatically overnight. Additional concerns with new snow over the melted-out older layers could mean you’ll find shallowly buried hazards such as trees and creeks. Especially on south-facing slopes you might collide with hard old debris piles  hidden by lower density new snow on top.

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