Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

Strong easterly winds will maintain dangerous avalanche conditions on Saturday. Numerous human-triggered slides occurred on Friday and are the most significant sign of instability. These aren't your typical PNW wind slabs, so avoid slopes over 35 degrees until the snowpack has time to heal. 

Problemas de aludes

  • Wind Slabs

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

    Our multi-day east wind event will continue transporting snow and creating irregular loading patterns. Expect existing slabs to thicken or new ones to develop on leeward slopes. They're likely on different aspects than you’re used to. They could also be further down in the terrain due to cross-loading. Look for actively blowing snow, new cornices, textured surfaces, or fresh drifts to help identify wind-loaded slopes to avoid. Thicker slabs could exist in rocky chutes, near the base of cliffs, or on convex rollovers. Using small test slopes or uptrack tests as you travel can help you determine how sensitive slabs are to human triggers.

    (2/16/2024)

    A snowboarder triggered avalanche on Pan Face at Mount Rainier National Park. This one came close to hitting a popular travel route for skiers and snowshoers.

    Note the blowing snow and textured surfaces indicating wind-loading.

    Photo: Daniel Jones

  • Storm Slabs

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

    In wind-sheltered terrain, plenty of recent storm snow exists. A gradual warm-up could help the low-density snow "slab up" during the day in areas further away from the east wind's influence. Use small test slopes, uptrack tests, or quick hand pits as you travel to look for heavy snow over weak snow, points of failure, or a poor bond to the old surface. If snow fails in blocks, you’re dealing with a storm slab issue and should avoid convex features over 35 degrees. In isolated locations, slabs could fail on weak snow grains, resulting in surprising avalanches that span far distances or connect terrain features.

    If the snow is light and fluffy but not well bonded, you may have to deal with loose avalanches running on an underlying crust.

    (12/8/2023)

    Hand pits are a great way to look at the recent storm snow. Look for strong over weak layers and places it fails easily. 

    Photo: Andy Harrington

Avalanche Discussion

The West South picked up roughly 1-1.5 feet of snow on Wednesday night and Thursday, creating the 2/14 interface. The storm was accompanied by strong east winds that continued to rip through the zone, especially near the crest. This prolonged east wind event should peak on Friday night before slightly tapering on Saturday. In areas further west, a warm-up may occur.

Friday was a reasonably active day in the West South. Human-triggered avalanches were reported in wind-effected terrain at Paradise and the Crystal backcountry. A small natural wind slab avalanche was also reported near Crystal. NWAC forecasters found a poor bond at the 2/14 interface in wind-sheltered terrain at Paradise and reported facets above the Early February Crust (EFC). During their mitigation work, Crystal Mountain Pro Patrol triggered several widely propagating slabs on the EFC. These 1-2 foot slabs were in previously unmitigated terrain and failed on weak snow above the EFC due to explosives or ski cuts. 

The strong winds from an atypical direction have created irregular loading patterns throughout the zone. Some areas have been scoured down to a hard crust, while others contain drifts, textured surfaces, or hard wind-effected snow.  Low-density cold snow exists in sheltered terrain but reportedly slowly gained cohesion on Friday. Sum it all up, and snow depths over the EFC will vary based on aspect, elevation, and exposure to wind. On slopes that typically receive direct sunshine, you'll find a series of crusts possibly interspersed with weak grains below the most recent storm snow. The 2/14 interface may contain buried surface hoar in wind-sheltered areas, and facets have been identified above the EFC. Investigate all the snow above the EFC for potential failures before committing to a slope. Where they exist, those weak grains could cause avalanches to break widely or in surprising ways, as we saw on Friday.

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