Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

Slabs will build as winds redistribute fresh snow near ridgelines and in upper-elevation terrain. Steer around steep slopes with active transport or wind-textured deposits 6" or deeper over a crust. Practice safe travel and limit your exposure to cornices or glide cracks as you ascend.

Problemi valanghivi

  • Wind Slabs

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

    The hazard on Monday will depend upon how much new snow falls and how strong the winds are to blow that snow around. The new snow should accumulate above a crust on all aspects, making it easy to evaluate the depth of snow and how much it has redistributed. Use a probe or pole to check for snow deposits 6" or deeper as you move through the terrain. Evaluate the bond to the crust using hand shears. Actively blowing snow, fresh cornices, and wind-textured snow provide clues to identify which slopes may hold wind deposits where you can trigger a small avalanche in steep wind-loaded start zones or on an unsupported rollover in the terrain. Shooting cracks, firm, or punchy surface snow layers serve as reminders to steer around slopes steeper than 35 degrees.

    (3/17/2023) Signs of wind transport like this can help you identify where slabs likely exist. Photo: Dallas Glass

Avalanche Discussion

Although you're most likely to trigger a wind slab, mild temperatures over the weekend brought some early spring hazards into play that could linger into Monday:

  1. Glide Cracks:  A frequent flyer on a steep, convex rollover on Ruth Mountain failed over the weekend and serves as a reminder about the unpredictable timing of glide avalanches (see photo gallery). While cooler, cloudy weather should start forming surface crusts, keep in mind that it will take a day or two for meltwater to stop draining and lubricating these interfaces. "Brown frowns" formed over the last several days and continued to grow on Sunday. Limit your time exposed to these open cracks on the slopes above you because a very isolated glide avalanche at the wrong time would be difficult to survive.
  2. Cornice Fall: Cornices are large and have sagged over the weekend. It's not clear how quickly they will firm up as temperatures cool. A cornice fall remains a hazard in its own right, but the weight of a cornice could be enough to trigger deeper layers in the snowpack that are no longer susceptible to the weight of a human. 

    We know of a few slab avalanches that released on Saturday: A 2' slab that released off of Mt Sefrit that was triggered by a natural small wet loose, and several very large (2-6') deep slabs triggered by Mt Baker Pro Patrol during avalanche mitigation Saturday morning. On Wednesday, a skier sustained serious injuries after being swept off of a cliff by a 2ft deep avalanche on Slate Mtn in the Baker backcountry. You can read the preliminary report HERE. On Friday, Lee Lazzara visited the site of the avalanche involvement and found that the slide ran on a slightly weaker layer of snow above a crust that formed on March 10th. Moving forward, we think that the increasingly unlikely event of a cornice fall would be necessary to trigger an avalanche on the 3/10 interface or deeper that would likely be unsurvivable.  Continue to limit your overhead exposure to this objective hazard on the slopes above and keep in mind that cornices have a way of breaking farther back than you expect.

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