Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Use caution in steep alpine terrain where you can still trigger an avalanche in wind drifted snow. Concerns for loose wet avalanches and cornice fall remain as the snowpack continues to thaw over the next 24 hours. Consult the West Central Forecast if you are in the southern portion of the zone, or traveling along the Highway 20 corridor. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Areas of wind-drifted snow linger in the alpine and are still reactive to the weight of a person on slopes greater than 35 degrees. These dense wind slabs may be anywhere from 6 inches to several feet thick. Use caution below ridge crests, in gullies, and around convex slopes that look heavily drifted, or present firm, hollow sounding snow. In addition, cornices remain a significant concern, especially with 6000ft freezing levels overnight and another warm spring day Thursday. Cornices are incredibly dangerous and unpredictable. Give them a wide berth along ridgelines and minimize exposure to alpine slopes where they loom above.

    (3/3/2021) Small skier triggered wind slab (D1) on a north aspect at 6000ft on the White Salmon Glacier. Photo: Pete Durr

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Another warm day will maintain the potential for loose wet avalanches on all aspects. Rollerballs and pinwheels indicate snow surfaces are wet and weak and that slopes are primed for loose wet avalanches. Steer away from terrain traps like gullies or slopes above cliffs that magnify the consequences of even a small avalanche. Keep in mind that wet loose slides in motion could even trigger slab avalanches. Seek out lower angled and supported terrain to reduce your risk. 

    Example of the type of natural avalanche we expect on Thursday Photo: Zach McGill

Avalanche Discussion

Wednesday was the warmest day in over a month with high temperatures of 40°F recorded at the Heather Meadows station. Snow surfaces in upper elevation, northerly terrain stayed cool and dry, while everything else was affected by the strong March sun. Cloudy skies and warm temperatures will continue overnight and through the day Thursday before another storm arrives. The transition to spring has begun, driving larger variations between aspects, elevations, and adjoining zones. 

Last week there was a widespread natural cycle that resulted in many very large avalanches (D3+) some of which hit Highway 20 just outside Newhalem. We believe most of these were big wind slabs, but there are several in the more southern part of the zone and one notable avalanche on Skyline Ridge (see gallery below) that may have failed on the deeper weak layer from January.  This layer is 200cm - 300cm deep in most portions of the zone and it should be hard for a human to trigger it. That said, a big cornice falling in the right spot might just do the trick. 

The take-home is that snow and avalanche conditions are variable in the West North zone and throughout the Cascades in general. In some areas, recent storm snow is stabilizing quickly, but a cluster of recent very large natural avalanches along the border of the Stevens and West Central zones continue to keep these old and deep weak layers on our minds in this zone as well. Read the West Central or Stevens Pass Forecasts to learn more about it. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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