Lawinenlagebericht

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Northwest Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Heavy snowfall and additional wind will maintain large and reactive slabs below ridgelines.  Wind slabs may be fresh or covered by lower density unconsolidated snow. Give typical avalanche start zones and wind-loaded slopes greater than 35 degrees additional time to stabilize.

Preliminary Report: On Saturday morning, December 11th, an avalanche fatality occurred in Silver Basin area of Crystal Mountain Ski Resort. See the forecast discussion below for additional details.

 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Large wind slabs formed Friday night as strong winds and heavy snow accompanied a frontal system. Low-density snowfall arriving through Sunday should be easily transported onto many of the previously wind-loaded slopes, slowing the stabilization process and forming new slabs in the process. Use visual clues such to read recent wind directions. Wind-stripped slopes suggest that wind slabs have formed on the opposite side of ridgelines. Steep, wind-loaded slopes may be tempting due to the additional coverage. You should resist the temptation. Instead, navigate to lower-angle slopes (less than 35 degrees).

    Example: Use visual clues to help you determine where Wind Slabs may be lurking near ridgelines.

    Photo: Andy Harrington

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    In less wind-affected areas, the snowpack has grown rapidly and has reached a threshold for storm slabs. With 6-12" of snow arriving through Sunday evening, you'll need to evaluate the potential for reactive interfaces between successive waves of snowfall. Cutting under a very small steep test slope can provide excellent information about the reactivity of potential slab layers. Only venture onto slopes steeper than 35 degrees after you have evaluated these layers and found them to be healing.

    Example: Simple snowpack tests like this can help you to identify interstorm layers that may be of concern. 

    Photo: Robin Pendery

Avalanche Discussion

The total snowpack at Hurricane Ridge has more than doubled since yesterday. Hurricane Ridge has around 2 ft of total snow and picked up 1.5 ft of new snow in the past 24 hours. The top 3-4 inches of snow fell Saturday with a cooling trend and may be right side up. Below that, expect an upside-down slab-like layer formed by heavy snowfall and a warming trend Friday night.  The warming and heavy snowfall coincided with the natural release of a small(D1) storm slab with a 1 ft crown, discovered by ONP road crews early Saturday morning at 4200 ft (S aspect). The recent snow sits above  5-6" of low-density recent snow (minimally impacted by wind). Digging down further, you may find a thin crust above a thin, sugary faceted snow layer, overlying the late-November Crust formed through repeated atmospheric river events. The late-November Crust may only exist at higher elevations and on shaded aspects. 

We're still in the midst of the first major storm cycle of the season with 6-12" of new snow arriving through Sunday. The snowpack has built from scratch in many areas. Roots and small trees poking out of the snow are a good reminder of the early season coverage. But the rapid change to the snowpack should give you pause and consider your terrain selection with caution. Use ridgelines, wind-scoured faces, and lower-angle slopes to navigate safely through the terrain. There's also significant uncertainty due to limited observations of the terrain. While Professionals got out in the immediate vicinity of Hurricane Ridge on Thursday, they were not yet able to travel widely, let alone on skis. Early season potential weak layers may exist and their reactivity remains poorly understood. If they were to be reactive, it would be now, following a significant loading event. The Silver Basin Avalanche described below represents a large and surprising avalanche in wind-loaded terrain from a nearby zone on Saturday. It serves as a good reminder to dial back your terrain selection and collect information before considering terrain that may increase your risk. 

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 a N to E facing slope at approximately 6500’. While all members of the party were initially caught, four were partially or 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.

Uphill travel reminder: Check in with your local ski area this weekend regarding terrain access and parking updates. Closed ski areas often share a similar snowpack and avalanche hazard as the surrounding backcountry. You may also encounter other hazards like active avalanche mitigation, unmarked obstacles, snowmobiles, groomers, and other heavy equipment as ski areas prepare to open. Be prepared to make your own assessments and handle emergency situations.

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