Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Points saillants

On Monday, there could be wind-loaded features to avoid on slopes where you’re not used to seeing them. Blowing snow can help you identify slopes that are actively loading. Uncertainty surrounding very large avalanches throughout the zone should give you something to think about before stepping into alpine terrain.

Problèmes avalancheux

  • Wind Slabs

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

    Cool easterly winds are expected to continue loading features and ridgelines at upper elevations on Monday. Although areas near the crest are typically more prone to east wind events, you should keep Wind Slabs on your mind regardless of your location. Wind Slabs formed by east winds are often on the opposite side of the ridge from where you are used to finding them. Additionally, there can be more cross-loading or mid-slope loading than our typical loading patterns. You can still look for textured snow surfaces or actively blowing snow to help you identify wind-loaded terrain to avoid. Firm snow that feels hollow and breaks off in blocks is an easy indication of wind-loaded terrain and you should avoid similar snow on steeper features. A wind direction change and increase in speed is expected during the daylight hours, so staying vigilant for freshly building slabs on all aspects will be a necessity throughout the zone. 

    (1/9/2022)

    East Winds were easily transporting snow on Sunday (1/9) to the opposite side of the ridgeline from where we typically see Wind Slabs forming.

    Photo: Andy Harrington

  • Loose Wet

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

    At lower elevations, a quick shot of rain may result in some Wet Loose avalanches on Monday. These avalanches often start at a point before entraining snow and fanning out as they move downhill. If it starts raining on snow in your location, you can avoid this hazard by avoiding steep slopes and keeping aware of the terrain above you. Warm temperatures and rain could also help blocks of snow and ice to fall from rock ledges, trees, or structures such as rooftops. The longer we have elevated freezing levels, the more likely these failures will be, even in areas or elevations where it is not raining.

    (1/9/2022) During the storm warming temperatures and rain produced a wet loose avalanche cycle and created rain tunnels on the snow surface near and west of the Cascade crest, like you can see here on Sprial Butte, White Pass, WA. Photo: Katie Warren

Avalanche Discussion

On Sunday, NWAC forecasters were able to get their first look at the backcountry after the recent stormy weather. In the Crystal area, we found plenty of evidence of recent avalanches, large and fresh cornices, and active wind transport from the east winds building shallow Wind Slabs. The real story, however, was finding another large-very large avalanche in Union Basin. This avalanche occurred on an E aspect at 6350’, and had a crown approximately 250 feet wide and 4-5 feet deep. The slide appeared to have occurred post-storm judging by how fresh the debris looked and ran approximately 800 vertical feet. This is the second very large avalanche reported in the Crystal area since the storm has ended. The first was a D4 avalanche triggered by Crystal Mountain ski patrol during mitigation work on Friday 1/7. 

Down near White Pass, NWAC forecasters were able to see very large avalanches near the Goat Rocks wilderness, meaning that these slides were not isolated to the Crystal area. Although many of these slides have occurred in wind-loaded terrain, similar very large slides in the neighboring Snoqualmie Pass zone have reportedly occurred on aspects that often don't see large amounts of wind-loading. 

If you are going to venture to alpine terrain, you need to know that very large slides may still be possible given a large enough trigger. These triggers are out there, it’s just a matter of if they fail and if they fail in the wrong place. As mentioned above, cornices have grown large and looked primed to fall on Sunday. A general warming trend may only enhance the likelihood of one of these potentially large triggers failing. Even a Wind Slab like we expect to see on Monday could step down into deeper layers of the snowpack given the right slope. Take this knowledge with you and talk to your partners about the added risk associated with your selected terrain. If you happen to be caught in one of these slides, it would most certainly be unsurvivable. 

If you are out and about and notice recent avalanche crowns or debris piles, please take a picture and share it with us as we try to track and document this cycle. The evidence of these avalanches may be hidden by some fresh snow sitting atop them, but we’d appreciate a picture of anything you suspect is an avalanche. Other useful information to accompany a picture is the location of the avalanche, along with aspect and elevation if possible. You can submit this information on our observation platform either privately or publicly. 

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