Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

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

Look for actively blowing snow, shooting cracks, or a firm hollow-feeling surface to identify wind-loaded features on Monday. East winds may result in new slabs or thicken existing ones. Weak layers deep in the snowpack should drive you to minimize time spent in big open terrain.

Problemi valanghivi

  • Wind Slabs

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

    Another east wind event is heading for Snoqualmie Pass on Monday. It could result in a fresh round of wind slabs or thicken existing slabs that formed on Saturday. East winds often result in more mid-slope cross-loading and reverse loading, creating slabs in locations you're not used to finding them. Look for actively blowing snow, textured surfaces, or fresh drifts behind objects to help determine wind-loaded features to avoid. If you're traveling over firm snow that feels hollow, you may be on a wind slab. Convex rollovers, the base of cliffs, or the sides of gullies are all popular places for wind slabs to form. Using small test slopes can give you an idea of how sensitive they may be.

    (1/14/2024)

    How many crowns can you find in this image? Note how most of them are on convex features or the base of rocks. Exactly where wind slabs like to form.

    [N Slope of Chair Peak]

    Photo: Steven

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    It's well understood that we have a poor snowpack structure roughly 4 feet below the surface at middle and upper elevations. The 12/30 and Solstice Crusts continue to produce failures in snowpack tests. That sets the stage for us to know the size and distribution of any potential avalanche on these layers. What we're missing from the equation is the sensitivity to triggers.

    We also lack the bullseye information of widespread avalanche activity on these layers. We know of one notable avalanche this week suspected on these layers. It was triggered by explosives at Alpental on Wednesday (1/10). These layers have been more active in the neighboring West South and East Central zones.

    The current thinking is that a more significant trigger may be needed to activate these layers, such as a step-down avalanche or cornice fall. It's not a sure bet, however. Take this problem into account as you travel, and if you want to minimize your exposure, stay off big open slopes where triggering this layer would likely result in an unsurvivable avalanche. 

    (1/10/2024)

    This very large avalanche released remotely from nearby explosive placement during avalanche control at Alpental. It is an indication that deeply buried weak layers could still be active. 

    Photo: Alpental Ski Patrol

Avalanche Discussion

It was a beautiful and crisp day at Snoqualmie Pass on Sunday. Winds eased significantly, and temperatures moderated slightly to make backcountry travel more palpable to the masses. The damage from Saturday's east wind event was not hard to spot. Crowns from wind slabs, textured surfaces, wind-stiffened snow, wind-stripped areas, and natural damage to trees were commonplace throughout the landscape. 

With the good visibility and travel conditions, crowns and avalanche debris from this past week's cycle started to come into focus. A ridiculous amount of crowns were spotted on the north slope of Chair Peak, with essentially every convex rollover containing one. The recent snow and wind mainly filled in what looked like a few deeper crowns, making it hard to pinpoint their size. 

Even though we downgraded the likelihood of triggering a persistent slab on Sunday, don't assume it's open season out there. We are operating with a high level of uncertainty surrounding that problem. You could travel all day and not see any signs of instability. We also wouldn't be surprised if a D3 avalanche occurred. We're living in the "scary moderate" world now, and it's not a fun place to be. Consider minimizing your exposure by sticking to smaller slopes and being aware of what's above you. 

Regioni coperte