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

Snowfall and strengthening winds will rapidly increase avalanche danger through the day. New slabs will form above weak or slick snow surfaces and could make for surprising avalanches. Monitor new snow depth and move to simpler, less exposed terrain as the storm intensifies and the snow deepens.

Problemas de aludes

  • Storm Slabs

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

    Moderate snowfall overnight will ramp up on Sunday and make for the first significant snow accumulation in weeks. In addition to the usual instability that comes with new snow, the variable old snow surface of slick crusts, facets, and occasional surface hoar will add a layer of uncertainty. On some slopes the new snow may bond well to the old snow surface, on others not so much. Test slopes, hand pits, and other snowpack tests will provide useful information, but the bond of new storm slabs to the old surface could be very different a short distance away.

    Human and naturally triggered avalanches will be more likely during periods of intense snowfall and wind loading. Wind loaded terrain will harbor thicker slabs, but all slopes with 8" or more of new snow should be considered suspect. Don't ignore obvious signs of instability like recent avalanches, shooting cracks and whumphs. While there may be little new snow in the morning, anticipate changing conditions through the day a be ready to move to lower angle, sheltered terrain as weather and stability deteriorate.

     

     

     

     

     

     

    Shallow slab avalanches in new snow layers are what you are most likely to see on Sunday. Avalanches in weak, faceted snow at or below the old snow surface could be larger and take you by surprise.

    Photo: Andrew Kiefer

Avalanche Discussion

An extended period of rain, then high pressure and warm temperatures, is finally ending as low pressure approaches from the northwest. The variable weather created a mix of snow surfaces that differ by aspect and elevation and even across a single slope. Slick rain crusts that actually made ski crampons useful, drifts of small faceted grains, extensive avalanche debris, sun crust - pretty much everything was out there besides cold settled powder.

The variable surface is adding to uncertainty about the bonding of new snow and wind slab layers. The greater mystery is a crust-facet combination just below the surface. In this instance, an old rain crust (buried January 6th, found 10-30cm down) has a layer of facets between it and the supportable surface crust. This crust-facet sandwich has been found throughout the Cascades near and above treeline - slopes receiving strong solar input have only a single crust at the surface.

This setup brings with it a high degree of uncertainty as it could do nothing or create big avalanches. While areas farther north in the Cascades may get enough load with the next storm to give this layer a good test, areas farther south and east may have to wait. Either way, it requires a conservative, wait-and-see mindset to safely figure out if this not-so-savory sandwich will be a passing fad or with us for some time.  

 

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