Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Warming temperatures, rain, snow, and winds will create dangerous avalanche conditions. You could easily trigger large avalanches in the new snow, particularly where the wind drifts snow deeper near ridgelines. Make conservative travel plans and stick to low-angle terrain while the storm runs its course. Depending on your elevation, you could see wet or dry snow avalanches. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    If you climb above the rain/snow line, conservative terrain will be key to avoiding storm slabs on Monday. As the warming storm deposits heavier snow over the recent light dry powder we enjoyed recently, avalanches will likely become easy to trigger on slopes above 35°. Avoid common trigger spots such as steeper, unsupported convexities even on lower angle slopes. There are observations of some older, weak interfaces where avalanches may fail within last week's snow. It will be a great day to stick to low-angle terrain and look for signs of instability, such as recent avalanches or shooting cracks. Using simple hand pits and test slopes, you can quickly assess how the new snow is reacting. If the new snow slides easily, you could trigger an avalanche on a steep slope. As you would expect, moderate to strong winds will accompany the storm. However, with some east flow through the passes, you could see wind loading on different aspects as you climb in elevation. Wind slabs will form overnight and continue to build during the day on Monday. Look for actively blowing snow and drifts behind rocks and trees to identify the wind direction and avoid steep wind-loaded slopes.

    (3/11/2023)

    A skier triggered this slab on a convex slope in the Alpental Valley on 3/11. Convexities are common trigger points for avalanches.  

    Photo: Jeff Tarshis

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    It's been a while since our last Cascade rain event, and while this storm isn't exceptionally warm, we will likely see rain near and above pass level. Previous sun and warm temperatures may have formed crusts that will hold off wet avalanches initially. Still, you can expect wet loose avalanches as the rain saturates the snow at lower elevations. These avalanches may start naturally with trees or cliffs shedding snow onto steep slopes, but you can also trigger these avalanches while skiing. Pay attention to overhead hazards and avoid getting caught in your sluff in steep consequential terrain. 

    (2/4/2023)

    This example of a small wet loose avalanche initiated from to steep terrain above. 

    Photo: Ian Nicholson

Avalanche Discussion

It will be two different worlds out in the mountains on Monday, with easterly winds and rain at lower elevations and southwesterly winds with dry snow at upper elevations. So be prepared to expect a range of snow and avalanche conditions as your travel. As snow and winds pick up, be leery of overhead cornices that have grown large during the recent windy weather. They could fail and trigger avalanches on the slopes below. The past week has delivered multiple small bursts of precipitation at the Pass, yielding 1.5-2 feet of snowfall. A few weak interfaces in the recent snow were associated with human-triggered avalanches in the Alpental Valley. While most of these occurred in wind-loaded terrain on convex rollovers or near ridgelines, 10-14 inches of new snow could overload these weaker interfaces in sheltered terrain. Avalanche professionals and recreationists alike have observed weak grains such as graupel and fragments of surface hoar. Some of these grains were at play when larger avalanches occurred within the zone last weekend. While we have maintained that the upper snowpack has been generally right-side-up throughout this period due to the lack of a significant slab, this storm will turn the favorable snowpack upside down. 

Régions couvertes