Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré last year. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Your main avalanche concern is newly wind-drifted snow that develops from the few inches of snow we'll get Sunday night into Monday. Drifts may be 6 inches or deeper, and where you identify new drifts that start nearing this depth, especially as you gain elevation, steer around steep slopes where you're most likely to trigger an avalanche. 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    You're most likely to trigger an avalanche in newly formed wind slabs from the snow that falls overnight Sunday and the last bit that comes in during the day Monday. We may only receive a few inches, but with moderate wind, slabs could be large enough to surprise you and take you for a scary ride. 

    Identify actively blowing snow, and watch to see where it lands. Search for wind-etched surfaces or smooth, pillowlike areas. You're most likely to get deeper drifts around rocky outcroppings, in gullies, or on the leeward side of slopes.

    Track changes in new snow depth. You could also identify  depths over the older, previously wet surface that is now at least a soft crust in most areas. This atmospheric river layer could be anywhere from a few inches to 18 or more inches below the surface. Snow just above this crust doesn't appear to be sliding any more, but it might when new slabs build on top. 

    Where you find deeper deposits, or if you feel firmer and heavier new snow layers, these are good indicators that wind-drifted snow is present, and it's best to steer around steep slopes, sticking to more sheltered or lower-angle terrain. 

    Example photo: A snowmobile-triggered slab avalanche with subtle wind-effect at the Baker NRA. This is similar to what you might be able to trigger on Monday. 

    Photo: Irene Henninger

Avalanche Discussion

A very large slab avalanche occurred Friday night in Hourglass, in the Baker backcountry. We suspect a cornice fall triggered the avalanche. It's unclear what layer the avalanche failed on, but it may have been as deep as the old February atmospheric river layer, which is around 4-6ft deep. This is likely a residual avalanche from our large atmospheric river warmup the previous week. 

I was in the Baker backcountry Sunday morning (observation). It's remarkable how many cracks opened up in the snow during and after the atmospheric river last week. It was also notable that the recent AR crust hasn't had a solid freeze yet, and I still easily punched through it with my feet at 5000 - 5500ft.  With a subtle cooling for the next few days, we suspect any lingering wet snow avalanche problems to finally be behind us, but it's not completely out of the question that a large cornice fall, glide, or block of snow perched on a steep rock face could still initiate an avalanche. 

Conditions could vary from the forecast depending on where you are in the zone. Start with this forecast before making your own observations to determine whether danger could be similar, higher, or lower based on where you are. 

Submit an observation to the website or the Avy App to help NWAC Forecasters reduce uncertainty. It can be short, simple, and even anonymous. 

Régions couvertes