Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
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2 · Moderato
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2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Your main avalanche concern is triggering wet avalanches on steep, sunny slopes. When you notice slopes getting sticky and wet, rollerballs running, or wet slides fanning out, consider changing aspects or sticking to lower angle terrain away from the bottom of steep slopes. Wind may transport low density snow that still extists at upper elevations into shallow slabs that could avalanche with a human trigger. 

Problemi valanghivi

  • Loose Wet

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

    Warm wet weather on Sunday led to wet loose avalanches on all aspects at lower and mid elevations. Sunday night skies cleared, and wet avalanche activity was limited to sunny slopes on Monday. Rollerballs and predominantly small, shallow avalanches resulted. You can expect similar conditions on Tuesday. 

    A distinct difference on Tuesday is that incoming clouds midday will likely have an effect on wet loose activity, as it could lead to one of two things happening: 1) wet activity could slow with clouds inhibiting the sun's intensity, or 2) cloud cover may cause "greenhousing", where snow on all aspects moistens and wet loose avalanche activity occurs everywhere.  

    Focus on snow surfaces around where you travel- Is the surface moist? Are you causing rollerballs or small shallow avalanches, or do you see them on steep slopes near you? If you say yes to any of these questions, it's time to start planning an exit strategy. Transition to cooler aspects or stay off and away from slopes steeper than 35°.

    Example photo: Rollerballs and wet loose avalanches like ones that you might see on Tuesday. Lake Valhalla area. 

    Photo: Brad C

  • Wind Slabs

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

    An easterly flow is expected to produce moderate winds at the pass. Low density snow still exists on shady slopes above about 5500ft, and wind could redistribute the light, dry snow into shallow wind slabs. Any avalanches will likely be small.

    Search for actively blowing snow, and textured or pillowlike surfaces. Feel for heavier snow surfaces. As any deposits will likely be shallow, you can dig down with your hand to see how deep these drifts are. Check to see how well they're bonded to the underlying snow. Long, shooting cracks from your weight are great clues a slab on a steep slope could avalanche. Avoid terrain over 35° if you identify any of these characteristics. 

    Example photo: Long, shooting cracks and wind-textured surfaces (both visible here) are great indicators the wind transport has occurred. The shooting cracks are obvious signs that an avalanche may occur on a steep slope. 

    Photo: Aldis Raisters

Avalanche Discussion

Snow surfaces vary quite a bit depending on where you travel. A breakable crust exists at most low and mid elevations. Sunny slopes will soften quickly and become moist. Prepare for challenging snow conditions during your outing. 

South-facing aspects that became sun-baked on Monday may not have as much avalanche activity as the previous day. Clear overnight skies will hopefully lock all surfaces up for Tuesday morning. Temperatures are supposed to get warmer during the day and with incoming cloud cover we're not sure exactly how the radiation balance will pan out and how much wet avalanche activity we'll see. 

Stevens Pass received 4" of snow Friday night into Saturday, and then Saturday night through Sunday morning another 8" fell. These layers came in relatively warm, with little wind. Early Sunday morning an abundance of wet or moist loose avalanches occurred naturally. Some of them triggered shallow storm slab avalanches in the new snow layer, like in the media photo. This was also the result of avalanche control work at the ski area. This weakness appears to be short lived, as tests produced only stubborn results on this layer on Monday. 

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