Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

Backcountry travelers continue to trigger avalanches in areas of wind drifted snow. Identify and avoid steep terrain where you find denser slabs sitting on softer snow below. 

Problèmes avalancheux

  • Wind Slabs

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

    Recent human triggered avalanches and wind loading show instability persists near and above treeline. Wind slab avalanches in near treeline terrain the past few days were not large, but all occurred in relatively small terrain features that limited avalanche size. Expect larger avalanches above treeline. You are most likely to trigger a wind slab on steep, unsupported features like convex rolls, hanging slopes, and steeper areas around cliffs and cornices. 

    As you gain elevation or move into open terrain take note of changes in the snow surface. Is one side of a ridge wind scoured while the other is not? Does the snow change consistency from light and fluffy to denser and more supportable? Using a probe or ski pole to locate deeper drifts, digging hand pits, and testing on very small slopes are simple methods that let you evaluate the wind slab problem as you travel. 

    (12/13/2021)

    Cross loaded terrain features on Shuksan Arm

    Photo: Lee Lazzara

Avalanche Discussion

Another small (D1.5) avalanche was reported in the adjacent West North zone on Monday. It was triggered on N aspect at 5000' with a ski cut in terrain steeper than 40 degrees, was about 1’ deep and 60’ wide. A stiffer layer of wind drifted snow above weaker, less dense snow was observed in nearby terrain. Also on Monday, an observer reported a small avalanche at Stevens Pass Resort, SE aspect at 5,400ft. Over the weekend, observers around Stevens Pass reported numerous avalanches running on layers within the recent snow. Most were small and human-triggered with a few reports of natural avalanches and slides up to size D2. 

Increased visibility allowed for observations of above treeline terrain around Mt. Shuksan with no new natural avalanche activity noted. Older avalanche crowns and debris piles covered with new snow indicate a natural avalanche cycle occurred in alpine areas on December 10-11th. 

Strong winds overnight Monday will yield to calmer conditions Tuesday. Expect an additional 3-6” of light density new snow with locally higher amounts.

The snowpack has more than doubled since December 10th.  Snowpack observations along the west slopes of the Cascades near treeline show snow depths of 3-6’ with a generally right side up snowpack structure. Although the new snow in wind sheltered areas is well bonded both within the storm layers and to the old snow surface, alpine winds may create instabilities in less sheltered areas. 

Preliminary Report: On Saturday morning, December 11, a party of six backcountry tourers were traveling uphill in a closed section of the Crystal Mountain Ski Area known as Silver Basin. The party triggered a large avalanche on an NE to E facing slope at approximately 6600’. While all members of the party were initially caught, four were fully buried. A nearby party of two witnessed the event and immediately assisted in the rescue. Crystal Mountain Ski Patrol was also notified and responded to the scene. Unfortunately, one of the fully buried victims did not survive. NWAC and Crystal Mountain Ski Patrol will collaborate to conduct an investigation. Our deepest condolences to the family, friends, and community.  SS-ASu-R3-D2.5-U; Crown Depth: estimated 2’ deep.

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