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 8 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Very steep slopes and features holding wind-drifted snow remain the primary hazard, especially at upper elevations. Pay attention to signs of wet avalanche instability as the day warms or if the sun makes an appearance.

Problèmes avalancheux

  • Wind Slabs

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

    Wind slabs are becoming harder to trigger, but they haven’t disappeared. As they stiffen, they may be less likely to release, yet more surprising if you do manage to find one. Fresher slabs may still exist in high-alpine terrain where winds remain strong enough to transport snow.

    Use rippled snow and scoured surfaces to identify wind-loaded terrain, and pay attention to changes in snow stiffness and depth. Test slopes and hand pits offer limited feedback with stiff slabs. The easiest way to reduce risk is to avoid very steep, unsupported, wind-loaded features and complex or rocky terrain where wind slabs linger.

    Also of note is a report of a human-triggered slab avalanche in a very steep but slightly wind-protected area. The takeaway is that some instability still exists in truly steep terrain. Don’t take stability for granted—use terrain to your advantage when stepping into steeper, more consequential lines.

    (1/15/2024)

    Example of wind-scoured snow on an exposed sub-ridge. Exposed crust is visible on the left side of the rounded ridge just above the center of the photo.

  • Loose Wet

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

    West North should be the slowest zone in the Cascades to warm on Monday, with cloud cover limiting how quickly wet snow problems develop. That said, any breaks in the clouds or periods of sun could tip the balance, especially on southerly aspects. Warming temperatures could also produce signs of instability on shaded aspects as well.

    Look for small loose wet avalanches initiating in steep, rocky, treed, or cliffy terrain as the day warms. Wet activity should remain limited in size, but conditions may change quickly if the sun breaks through. Keep an eye on what’s happening above you. Rollerballs and very small loose snow avalanches are clear signs that the snow surface is warming and becoming unstable. 

    (3/13/2022)

    Sticky snow and rollerballs are typical first signs that the snow surface is warming.  

Avalanche Discussion

Observers in the Baker Backcountry reported that yesterday’s fluff had settled into a more cohesive layer. Clouds and light snow flurries were a big contrast to the full sun on Saturday and helped keep snow surfaces cool despite warmer temperatures (+10 degrees at 5000 feet). The most notable observation was a report of a human-triggered avalanche on a steep east aspect of Table Mountain at 5,000 feet. The slab released above the December 24 crust. Another human-triggered wind slab avalanche was reported on Happy Bunny Butte/Video Peak near the east end of Ptarmigan Ridge.

The 1–2 feet of snow that fell Wednesday afternoon through Friday has begun settling over the crust. For the most part, bonding within the new snow layers and at the crust–new snow interface has grown stronger, but instability can still be found in steep terrain. The crust can be found anywhere from near the surface to over 2 feet deep, depending on aspect, elevation, and exposure to wind and sun. A surface sun crust was reported on some southerly aspects.

Régions couvertes