Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Pay attention to the slopes above you. Rain at all elevations could cause isolated chunks of the snowpack to avalanche. Consider routes and travel techniques that limit your exposure to steep rocky slopes, especially when you notice crevasse-like cracks.

Avalanche problems

  • Glide Cracks

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Glide avalanches typically occur on isolated slopes where the snowpack rests on smooth ground such as a rock slab or grassy area. That can be hard to figure out when buried under the snow. With a shallow early season snowpack, rain may quickly reach the ground allowing it to become wet and weak. Predicting when and where this process will take place is extremely difficult, however, a resulting avalanche would be large and potentially deadly. Consider alternate routes that lead you around instead of under any steep rocky slope. Crevasse-like glide cracks can serve as an indication that water at the base of the snowpack is making it unstable.

    (12/7/2020) Example Snoqualmie Pass: Glide cracks like this can indicate water reaching the ground and causing the base of the snowpack to become unstable.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Weather forecasts call for substantial rain well above our forecast area. The rain should initially impact mid and upper elevation terrain on W-N-E aspects that still harbor dry snow. If you see new rollerballs or find the snow surface becoming wet and sticky, anticipate loose wet avalanches and stay off similar slopes greater than 35 degrees. By late afternoon, additional rainfall could eventually weaken firm surface crusts and wind packed snow formed over this past week, and allow wet avalanches to become larger and more widespread across the area.

    (11/27/2020) Example: New rollerballs at Mt Rainier. These indicate the snow surface becoming wet and unstable.

Avalanche Discussion

The West-Central region should fall just within the band of heaviest precipitation Tuesday allowing substantial rain to impact all but the very tallest mountains in the zone. Weather models disagree with total precipitation amounts, but we expect more than an inch of water by Tuesday afternoon. If the bulk of the moisture stays further north or you travel closer to I90, you could experience slightly lower avalanche danger. 

Despite the incoming rain, the snowpack should handle the water fairly well. Observations from the zone indicate a strong and well-settled snowpack. Over the last week of calm weather, variable snow surfaces developed with a healthy mix of soft powder, stout crusts, and firm wind deposits. This variability will cause the timing of the rain affect to differ from slope to slope. Snowlines around the zone range from 2500-3000’. Even with a healthy early season snowpack, numerous obstacles such as trees, rocks, and open creeks still exist. Give yourself plenty of time to navigate around these hazards. 

Regions covered