Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

As the storm continues Friday across the West South expect avalanches to become larger and more widespread. While the biggest slides will likely occur in wind drifted snow at upper elevations, the growing snow totals should cause you to pause. Seek out areas where you can easily identify and avoid steep open slopes.

Problèmes avalancheux

  • Wind Slabs

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

    Very strong winds throughout the storm easily transported snow, sculpted the surface, and formed slabs at mid and upper elevations. On Thursday human triggered avalanches were reported from both the White Pass and Crystal Mt areas. While you’ll likely see wind slabs along exposed ridges, you could also find them at the tops of chutes, along mid-slope gullies, and near the base of cliffs. These slabs may continue to grow Thursday night and Friday allowing them to become large enough to bury and kill you. As the winds die down, a few inches of soft snow may start to hide these potential avalanches from view. Look for obvious clues like drifts and cornices to figure out which slopes could hold wind slabs. Given this potentially large and hidden problem, allow plenty of space between you and any steep wind-loaded slope.

    (12/23/2021)

    Intense blowing snow was encountered Thursday (12/23) on the Paradise parking lot. When you see wind transported snow, anticipate wind slabs in near by terrain. 

    Photo: Mt Rainier Rangers

  • Storm Slabs

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

    Even as cooling temperatures allow the storm snow to fall “right-side-up,” at some point the growing snow totals become concerning. You may trigger an avalanche within the new snow on very steep slopes and convex rollovers. These slides could be loose or more slab-like. Either way, as the snow stacks up, these avalanches could grow large enough to bury you. Use small slopes and up track tests as a way to see how the snow reacts. If you cause long cracks or small avalanches, it's a good sign that you should stay off of larger steep terrain. 

    Observations in wind-sheltered areas Thursday reported good and generally stable travel conditions. However, two notable reports from nearby Snoqualmie Pass are worth mentioning.  A skier triggered a small soft slab on a steep SW aspect at 4800’ (see photo below). This slide emphasizes the potential for slab avalanches even in this very soft snow. Two parties also reported graupel falling during the storm (see photo below). These Beebee-like grains are often the culprit in storm slab avalanches but can be localized to specific mountains or drainages. You'll need to dig in the snow to see if they exist in your area.  If you see them, dial it back and stay off of all steep open slopes.

    (12/23/2021)

    Uptrack tests and small slope can help you see how the new snow reacts under your weight. 

    Photo: Shane Robinson

Avalanche Discussion

For areas further south in the zone like Mt St Helens and Mt Adams, significant snowfall and strong winds could create locally High avalanche danger. You may have noticed the Mt Hood zone rated High at mid and upper elevations. Take the time to read this forecast as well. Consider limiting your exposure not only to where avalanches start, but also to where they run and stop. 

Snow continues to pile up with this storm. Most areas receive 10-18” of snow as of Thursday afternoon. The snow sits above the Solstice Crust/Interface. In some locations this crust is thinner and more aspect dependent, becoming more prevalent on southerly slopes. In other locations, you may find it is thicker and located around the compass dial. As you ascend in elevation it may become less noticeable. So far, we haven’t received word of any notable avalanches on this layer. However, if you dig in the snow, it may serve as a snowpack marker and potential layer of interest. Observations continue to report a good bond between the new snow and this crust. 

As temperatures become quite chilly over the next 24hrs, expect snow to water ratios to increase. You may find more snow on the ground than the weather stations indicate. 

Régions couvertes