Boletín de aludes

West Slopes Central

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

Heavy snowfall near Highway 2 and the Mountain Loop will increase avalanche danger at all elevations, especially on wind loaded slopes. Stick to lower angle, sheltered terrain until the weather improves and danger diminishes.

Problemas de aludes

  • Wind Slabs

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

    Though snowfall during the day Sunday appeared minimal, nearly a foot of wet, dense snow drifted into leeward start zones in areas that received snow first. These slabs will grow deeper overnight with more snow and strong winds. Surprising avalanches could occur where new wind slabs overlay slick crusts, weak faceted snow, or other suspect layers near the old snow surface (photo).

    Big changes in new snow depths over short distances were reported on Sunday. Identifying areas of deeper wind loading was tricky as dense new snow kept observers on the surface whether it was 2” or 10” deep. Dig down into new snow or use the handle of a ski pole to track the depth of new wind slabs over the old surface crust. Use hand shears and test slopes to evaluate the bond of new wind slab layers and consider simply avoiding steep, wind loaded terrain until the snowpack has time to gain strength.

    (1/30/2022)

    New 10" wind slab over old surface crust (upper interface/line) on a N aspect at 4600'. Heavily rain affected and frozen snow from the lower interface to the bottom of the pit. The layer between the two traced out interfaces is the weak, faceted part of the crust-facet combination we are wary of

    Photo: Lee Lazzara

  • Storm Slabs

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

    Moderate snowfall overnight will increase early Monday 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 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.  Reduce uncertainty by choosing simpler terrain with less exposure to avalanches.

     

     

Avalanche Discussion

While Heather Meadows in the West North picked only 2" of new snow from  1.5" of precipitation (as of 5pm Sunday), much deeper, wind drifted snow was found just higher near treeline. As of this evening, the rain and snow are working their way across West Central with up 1" of precipitation farther north in the zone vs. a fraction of that at Stevens Pass. Expect sustained snowfall as snow levels sharply lower and a convergence zone kicks in around Highway 2 tonight and lasts through Monday.

Poor visibility limited avalanche observations into higher terrain. Limited snowpack observations found wet new snow made for a good bond between new slabs and the wide variety of old snow surfaces.  Higher elevation terrain may have retained a weaker old snow surface that was buried with drier, colder snow.

A deeper concern is a crust-facet combination just below the surface. In this instance, an old rain crust has a layer of weak snow between it and the surface crust above. This crust-facet sandwich has been found in various iterations throughout the Cascades near and above treeline - slopes that received strong solar input have only a single crust at the surface. This layering brings with it a high degree of uncertainty as it could do nothing with additional load or create big avalanches. Limited testing has shown inconsistent results at this layer. It could be worth adopting a more conservative terrain mindset until more information is gathered.

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