Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

To celebrate the New Year keep your terrain selection reigned in Friday and steer around all open slopes greater than 35 degrees. At upper elevations, several recent slab avalanches highlight the continued danger within the recent snow. At mid and lower elevations, warm temperatures and rain may cause the snow surface to become wet, unstable, and slide downhill.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Several avalanches occurred within and at the base of the storm snow Thursday around the West South Zone. Some of them were large and wrapped around terrain features. You can still trigger avalanches on New Year’s Day on open slopes greater than 35 degrees. While small slope tests and hand-pits may allow you to look at shallow storm snow layers, the recent snow is rather dense and many of the weaker snow grains are located deeper near the most recent interface (12/29). This means you could travel around all day and not notice obvious signs of unstable snow. In areas where you see signs of wind transported snow, deeper avalanche may occur. 

    At least one avalanche at White Pass (E, 4500’) failed on a layer of buried surface hoar Thursday. Another, widely propagating avalanche at White Pass (NE 6300’) is believed to have failed on this same layer. Other observations including whumphfs and shooting cracks point towards the same concerning theme. Surface hoar was observed prior to this storm at White Pass, Paradise, and to a lesser extent Crystal. If an avalanche fails on this layer it could trigger remotely, propagate widely, and act in surprising ways. Even though we’re forecasting Storm Slabs, approach these storm slabs with greater caution and give them longer to heal. We will continue to pass along information regarding a potential persistent weak layer in our forecast.

    (12/31/2020) Large slab avalanche near White Pass Thursday. NE-E 6300' Gunsight Bowl. HS-ACu-D2.5-R3-I. This avalanche wrapped around multiple terrain features.

  • Loose Wet

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

    As temperatures rise Friday, rain will reach into the near treeline band falling on cold dry snow. As it does so, you may see the surface snow become wet and unstable. Fortunately for us, this rain event isn’t particularly wet, and that should limit the avalanche activity. If you see new rollerballs or find that the snow surface feels wet and heavy, steer around nearby slopes greater than 35 degrees. While it may take some effort for these loose avalanches to get moving, once they do, there’s plenty of snow for them to entrain as they descend.

    (11/27/2020) Pinwheels are a clear sign the snow surface is becoming unstable.

Avalanche Discussion

The West-South zone received significant snowfall since the 29th. (Paradise: 26+”, Crystal 10-14”, White Pass 18-22”). Oscillating temperatures and strong winds created slabs in many areas. The most recent interface (12/29) can be difficult to find. On more southerly slopes it may be marked by a thin meltfreeze crust. 

Cornices along ridgelines grew significantly over the past week. Many of these features are thin and weak. On Thursday, NWAC staff unintentionally triggered a cornice from more than 10’ away. Give these touchy mountain features a wide berth. 

In locations that received less snow, expect avalanches to be smaller. You may find slightly lower avalanche danger in theres locations. However, with the potential for a persistent weak layer in the snowpack. Ease into the terrain and gather information before committing to larger and more consequential slopes. 

Happy New Year from all of us at NWAC!

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