Boletín de aludes

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Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
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

Winter will finally make another appearance, and a storm will bring strong winds, new snow, and dangerous avalanche conditions. Avoid steep slopes in wind-affected terrain, especially at upper elevations and in wind-exposed terrain where the wind will create deep drifts of snow. Although the chances are low, smaller avalanches may step down to deeper weak layers and become large.

Problemas de aludes

  • Wind Slabs

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

    While precipitation totals aren't remarkable for this storm, the associated strong winds will drive dangerous avalanche conditions. You may find wind slabs in unusual locations and lower elevations than you usually expect. The wind will deposit snow on various surfaces, including icy crusts and weak snow resting on the recent Valentine's Day crust. Wind slabs are most likely to be located in open terrain and will increase in size with elevation. Avoid steep terrain in wind-affected areas. Look for visual clues such as cornices, blowing snow, or wind textured surfaces to identify wind-affected terrain. Watch for signs of unstable snow, such as shooting cracks or collapsing. Sunday will be a good day to seek out terrain sheltered from the wind. 

    (12/29/2021)

    Small wind slab off Delancey Ridge on the 29th.

    Photo: Will Govus

  • Persistent Slabs

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

    Snowpack tests have indicated that large persistent slab avalanches are still possible on shaded slopes above 5,000ft. New snow and wind will test these weak layers, and a shallow wind slab could step down, resulting in a larger and surprising avalanche. Sunday will be a good day to avoid shallow, rocky, or very steep unsupported slopes on northern aspects where this snowpack structure likely exists. Indicators of persistent slabs are whumphing collapses and snowpack tests that pop or drop suddenly. Avoidance of slopes where we know the recipe exists for these avalanches is really the only way to be sure to stay safe, even though chances of triggering one of these may be low. You can dig down and find the late-January weak layers 1-2 feet below the surface. This layer is a combination of weak sugar-like facets sandwiched between two crusts in many areas. Sometimes you'll find weaker snow or old surface hoar above the upper crust. The weak layers are deepest near and west of the Cascade crest and in wind deposited zones. The crusts may be found near the surface in the eastern part of the zone and in wind-scoured areas.

    (2/5/2022)

    A skier triggered avalanche near Maple Pass. Three people were caught, one was carried over 400ft with no injuries. E, 6,600ft

    Photo: NWAC public obs

Avalanche Discussion

While we are all looking forward to some long-awaited snowfall, existing various slick and weak surfaces may not form a good bond with the new snow. The Valentines Day crust is now buried by a few inches of snow in some areas and may still be on the surface further east. Observers found weaker snow beneath and sometimes above this thin crust in high, shaded locations during the week. Approach new terrain slowly and cautiously and investigate these shallowly buried interfaces. Quick hand pits are a great way to identify poor bonding with underlying surfaces. 

Last week observers have targeted the late January weak layer. The one thing in common is that most tests produced sudden collapse results. In general, shaded, northerly aspects are still showing the most potential for human triggered avalanches where the crust-facet sandwich is most defined and weakest. The most recent natural avalanche on this layer was a D1.5 on a rocky, unsupported east aspect, near treeline on Porcupine Peak (see photo). On Thursday and Friday, observers got propagating test results with extended columns and moderate force on N and E aspects between 5,700ft and 6,500ft. Last week, observers noted a cornice fall that triggered a large wind slab avalanche in rocky north-facing terrain. On February 5th, a notable avalanche was triggered near Maple Pass on an east aspect, near treeline. The slide likely occurred on the late January PWL and involved 3 people, carrying one over 400ft. Widespread whumpfing, rolling collapses, and remote triggering of avalanches were all common last week, though these direct signs of instability have become less frequent in recent days. The recent warm temperatures have helped the snowpack and late January weak layer gain strength, but the instability continues to linger.

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