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
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Rain will maintain unstable wet snow, especially at higher elevations where there isn’t a protective icy surface. These wet avalanches are very hard to predict and have huge consequences. Stay off of steep open slopes and limit any time you spend underneath them.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2.5

    It’s hard to put a name on the wet avalanche problems you may encounter Monday at mid and upper elevations around the Pass. You could see loose wet, wet slab, glide, and cornice issues. With so much water in the snowpack, sometimes snow simply sheds from rocky faces. Conditions like these demonstrate it’s more about the consequence of larger and more powerful avalanches than whether or not you can trigger any individual slope. So, besides staying off of open slopes greater than 35 degrees, you may also want to minimize any time use spend traveling underneath them. Even crossing an avalanche path carries with it more risk than normal. 

    At lower elevations, an icy surface should help limit any avalanche concerns. As more rain falls, this crust could break down in certain locations. If you notice this occurring, recognize that the danger is also increasing. Rollerballs and small point-release slides will help you know to avoid similar slopes.

    (12/24/2022)

    Example: A large natural wet avalanche below treeline in Mt Rainier National Park from Christmas Eve. You could see similar slides on Monday. 

    Photo: NPS Rainier Rangers

Avalanche Discussion

The last several days have been a roller coaster ride at Snoqualmie Pass. Below zero temperature on 12/23 swung to the 40’s on Christmas Day! Snow, rain, sleet, and freezing rain all occurred. Exactly how precipitation fell as rain is tough to say. Our precipitation gauges filled with sleet and ice (see photo), which eventually melted out as temperatures warmed. On the ground observations have been limited, but Alpental Ski Patrol and WS DOT provided some insight. At Pass level, several inches of sleet was eventually capped with a very stout icy crust. This could make travel very challenging and potentially dangerous. Slightly higher in the terrain (4500ft) freezing rain formed a much thinner but very solid layer of ice across the mountains. Higher still (5500ft) periods of rain and freezing rain limited crust development. 

So, at higher elevations rain fell on a very cold, dry, and layered snowpack. It’s reasonable to believe that at least some natural avalanches occurred during the heart of the storm on Christmas Eve. However, how many, how big, what type, and on what layer, all remain unknown. In short,  different elevation bands could be in very different places in their avalanche cycle depending on exactly how much rain has fallen and the thickness of any protecting ice lens.

Even though temperatures should cool slightly Monday, it will take a more significant cold snap to lower the avalanche danger and shift to dry snow problems.

Régions couvertes