Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Snowfall and strong winds will taper on Monday but will leave behind slabs of wind drifted snow near and above treeline. Identify and avoid steep terrain with recent wind loading to reduce the risk of triggering an avalanche.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Though snowfall during the day Sunday appeared minimal, nearly a foot of wet, dense snow drifted into leeward start zones. These slabs will grow deeper overnight with continued snowfall 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'. Rain affected, 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.

    Photo: Lee Lazzara

Avalanche Discussion

While Heather Meadows 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. 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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