Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You may need to manage both wet and dry avalanche problems on Wednesday as our weather pattern shifts. Use the moisture content of the snow surface underfoot as a proxy to determine what issue you may be dealing with. You should make travel plans that give you plenty of options to adapt to changing conditions throughout the day.

Avalanche problems

  • Loose Wet

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

    With a bump in temperatures and fewer convective showers forecasted for Wednesday, it’s time to start talking about wet avalanche activity more formally than the past few days. You could run into issues if solar input is able to destabilize the recent cold dry snow sitting on the surface. If the snow is getting wet and sticky, shedding from trees and rocks, or there are new rollerballs on steep slopes, then Wet Loose avalanches could soon follow. These slides typically start at a point and fan out as they move downhill, sometimes growing large or triggering slabs in the process. Your best mitigation strategy will be to head for shaded slopes with limited overhead hazard.

    On slopes that continue to hold cold dry snow, you could trigger some Dry Loose avalanches that behave similarly to their wet counterparts. Don’t get swept off your feet in consequential terrain.

    (3/18/2023)

    Example: Wet Loose avalanche on a steep sunny slope. Note how it originated at a point, near trees and rocks.

    Photo: Dallas Glass

  • Wind Slabs

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

    You may still be able to trigger lingering slab avalanches in wind-effected terrain. Focus your attention on specific terrain features such as steep unsupported slopes, convexities, confined chutes/gullies, or the lee side of ridgelines. These are the most likely locations to trigger one of these slides. Visual clues such as textured surfaces or recently formed cornices can help you identify aspects where these slabs may be lingering. In some locations, they could be hidden under a few inches of snow. If that’s the case, you’ll need to feel for differences in density under your feet to locate them.

    On Mount St. Helens, the potential exists for larger and more destructive hard slab avalanches. Multiple slides with 6-foot crowns were triggered on Mount Hood on Monday. Check out the Hood forecast for more information.

    (4/3/2023)

    A group intentionally triggered this Wind Slab by dropping a small cornice on the slope. It failed 6-10" deep. [White Pass E/SE 6500']

    Photo: Susie Glass

Avalanche Discussion

Wednesday should be the warmest and potentially sunniest day of the week as we transition between weather systems. That doesn’t mean you won’t still see a convective shower or two, but they should be few and far between. The trade-off is that you’re more likely to encounter avalanches due to solar input than in recent days. The timing will have to work out between chilly morning temps and increasing clouds in the afternoon. Areas further south will cloud up first as the storm works its way northward. On some slopes, a surface crust may need to break down before the threshold for wet avalanches can be reached.

We’re continuing to focus our attention on the storm snow sitting above the 3/31 interface. Its depth varies from roughly 1 foot below the surface at Crystal Mountain to approximately 2.5-3 feet below the surface at Mount St. Helens. This crust could prove to be a good bed surface for avalanches to run on, whether slabs or loose.

Over the weekend, a handful of human-triggered avalanches were reported near Crystal Mountain and White Pass. Most of these were on steeper terrain features and all involved failures within or at the base of the recent storm snow. Near Crystal most slides were in areas that had become sun affected during a break in the cloudy weather. Down at White Pass, most were in wind-effected terrain near ridgelines. The chance of triggering similar avalanches near the crest may have diminished but has not been eliminated.

We have no recent observations from the volcanoes where we continue to have a higher degree of uncertainty. When uncertainty goes up, your terrain selection should go down. Consider reading the Mount Hood forecast before traveling on the southern volcanoes to get a better feel for what you could encounter.

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