Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

Very dangerous avalanche conditions are expected on Thursday, and large, natural avalanches will be likely. A storm will bring around 2 inches of water during the day, and freezing levels will slowly rise so that heavier snow or rain will fall on top of the underlying lighter snow, causing an unstable snowpack. Travel in avalanche terrain is not recommended, which includes not only steep terrain but also lower angle or flat runouts beneath avalanche paths, even at lower elevations where a large avalanche path sits far overhead that could run down and hit you. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–2.5

    Dry slab avalanches will grow in size and become more dangerous and reactive as the day progresses. The day may start out with Considerable avalanche danger, but expect the danger to rise to High as more snow falls and temperatures increase. Storm slab avalanches could fail in the new snow, which may be as deep as two feet at the upper reaches of our forecast zone. However we've seen a lot of avalanche activity in the last few days with most avalanches occurring one to two feet deep. These layers may not be completely healed by the time the new snow comes in, so avalanches could fail on these older layers, making upper-elevation avalanches three or more feet deep. Earlier in the day avalanches could be smaller, but they will increase in size as our snowpack grows. Expect avalanches to be large, or possibly even very large.  Smaller storm slab avalanches are expected to occur in upper portions of below treeline areas, before the snow gets wet. 

    Rising temperatures have two important factors to be aware of: Firstly, relatively cooler, lighter, snow will fall before heavier, denser snow that comes with the temperature increase will fall on top, leading to an upside-down snowpack. Upside down snow tends to be unstable, where the lighter, weaker underlying snow fails under the weight of the heavier snow on top, and an avalanche occurs. Thursday is the perfect setup for natural slab avalanches, which you can expect to see as the snow builds up. The other concern with rising temperatures is rain, which is discussed in the next avalanche problem. For the storm slab avalanche problem, we've got a dangerous setup that will continue to grow on Thursday. Natural avalanches are likely and human triggered avalanches are very likely, so traveling in avalanche terrain is not recommended. 

    (1/10/2023)

    Natural slab avalanches which occurred in the Baker backcountry early Wednesday. Avalanches could fail within the new snow, or could step down to these layers on Thursday. 

    Photo: T Papritz

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–2.5

    Wet snow avalanches will develop into a dangerous problem as the day progresses. Snowlines are forecasted to rise to 6500ft by Thursday evening. As the rain slowly encroaches on the dry snowpack at higher elevations, your dry snow avalanche concerns will transition to wet ones. They may start with small wet loose in the upper reaches of below treeline areas, where previous low-density snow existed. The wet loose avalanches will slowly shift higher, reaching all the way into above treeline elevations as the rain reaches higher elevations. As more rain falls and percolates into the snowpack, unpredictable wet slab avalanches are expected. There may also be glide avalanches running on steep slopes with smooth, underlying bed surfaces as well.

    The wet slab avalanches could fail as deep as the dry snow avalanches. They could be a mix of wet and dry snow, progressing to more wet as the day progresses. Wet slab avalanches are not something to tiptoe around, and this is a day where it's a good idea to stay off steep slopes and runouts beneath avalanche paths. 

    (1/14/2022)

    A natural wet slab avalanche triggered by heavy rain last year. SE aspect ~6000' above Schriebers Meadow. This is probably larger than it looks, but ones we may see on Thursday will probably mostly be larger than this one. 

    Photo: Graham Clark

Avalanche Discussion

This is pretty simple: A big storm's here, temperatures will be warming throughout the day, and we'll be getting a dangerous, unstable, upside-down snowpack. We'll even see rain on the snow in near treeline and lower parts of above treeline areas as the day progresses. This is a recipe for avalanches, and if you're going to get out, stick to low-angle terrain and stay far from the bottom of steep slopes. Natural avalanches from upper elevations may be large enough to run into below treeline areas. This could affect mountain roads, even if you're down at the bottom of a valley. The most obvious indicators of an avalanche path running into lower elevations is a gully or opening in trees extending uphill to a steep start zone several thousand feet above, which could be out of sight. 

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