Boletín de aludes

West Slopes North

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

You're most likely to trigger an avalanche on wind-loaded slopes near and above treeline, and the avalanches could have characteristics slightly different than your usual slab avalanche. Some areas in the zone are more wind-affected or may get more snow than others, and slabs may be more reactive in those locations.  Search for signs of wind loading like visibly textured surfaces, slightly firmer feeling snow, or hints like long, shooting cracks from your feet, as indicators to steer around nearby steep slopes. 

Problemas de aludes

  • Wind Slabs

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

    You could trigger wind slab avalanches in shallow new drifts around 6 inches deep, or possibly at the bottom of the new snow layer around a foot deep. Wind slabs that formed in the last couple of days could be hidden under snow that fell with no wind. In some places, a weak, old snow surface of facets or surface hoar was present. This means that triggering a slab could be easier than usual. Avalanches could also occur at slightly lower angles than the usual upper 30 degrees, as reported in THIS observation from Sunday, and they might propagate a little further than suspected. 

    Look for signs of wind-affected snow like scoured ridgelines, fresh cornices, and smooth drifts to figure out the wind-loading pattern in the surrounding terrain. Keep track of differences in the feeling of snow underfoot- if snow feels light versus feeling stiffer or heavier. Deeper snow and softer layers below likely means less or no wind loading, as opposed to stiffer snow underfoot probably meaning wind slab.

    Consider investigating for weak snow that could be at the new/old interface. Test slopes and other assessment tools can help you evaluate the reactivity of slabs on underlying layers. Shooting cracks mean you found a reactive wind slab. If you identify wind-loaded areas, this is where your chances of triggering and getting caught in a large avalanche are greatest, so steer around slopes above 30 degrees when you identify any indicators of wind loading. 

    (2/26/2023)

    A soft wind slab triggered below a cornice on a suprisingly low angle slope, near treeline. The slab was 8-10" deep at the initiation point. Slab propagated the entire length of the cornice, approximately 30' wide. 

    Photo: Public Observation

  • Loose Dry

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    An abundance of low-density, cold, dry snow exists. We've received many reports of dry loose avalanches, or sluffs in the last few days. Some of these have been an unusual mix of a very soft slab and sluff combination, like the accompanying photo. Some sluffs are just running in the top layer of snow, but there's a small chance that some may be running as deep as the new/old interface about a foot down. 

    A sluff probably isn't going to be large enough to bury you, but it could take you for a scary ride if it catches you unaware.  In general, these are more predictable, and you can expect to trigger one as you're making your way out onto a steep slope. Remain alert for snow moving around you while in steep terrain, and get off to the side if large amounts are present. 

    (2/26/2023)

    This is a bit of a combo loose dry/soft slab avalanche, which has been a frequent occurrence the last 2 days, from a ski cut. This was about 10cm deep.

    Photo: Public Ob- Camden Latimer

Avalanche Discussion

Forecaster Lee Lazzara traveled to the Baker NRA Monday and found surprisingly deep snow. That area has been receiving more snow out of the last few storms than other locations, making for several feet of low-density powder and more challenging travel. There was also more wind to form reactive slabs. Lee saw several natural small (D1) avalanches which had occurred in the last 24 hours, and some older ones which were medium (D1.5) in size. In general, locations closer to the Highway 20 corridor may have received more wind than areas further north.

Keep in mind that although many recently reported avalanches have been smaller, they've caught people off guard with slightly unusual characteristics like lower slope angles, long propagations, or traveling fast and far. If you're in high-consequence terrain or in a terrain trap,  the avalanche could still be enough of a problem to kill you. 

 

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