Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Strong to extreme wind speeds, new snowfall, and fluctuating freezing levels should all combine to create dangerous avalanche conditions around the West South zone on Thursday. Keep it simple by looking for red-flag signs of instability such as shooting cracks, recent avalanches, or whumpfing collapses as an indication that the snowpack is unhappy. If you notice the signs, stay off slopes over 35 degrees until the storm has run its course. 

Avalanche problems

  • Wind Slabs

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

    This is going to be a windy storm in the West South zone. Expect to encounter significant blowing snow that is actively wind-loading the lee side of ridgelines, confined gullies, or convex slopes. It shouldn’t be difficult to determine which way the wind is blowing, helping you identify wind-loaded aspects to avoid. If you notice cracking of the snow surface or encounter firmer feeling snow as you travel, you’ll know you found a Wind Slab and that you should retreat to slopes under 35 degrees. 

  • Storm Slabs

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

    Even in areas protected from the wind, you could find slabs that are reactive to human triggers. Fluctuating freezing levels, reported weak snow surfaces, plus a few crusts for snow to run on all point toward more widespread Storm Slabs. Use hand pits, uptrack tests, and small test slopes as you travel to look for a poor bond to the old snow surface or storm snow that has come in upside down (heavy snow over weaker snow). Similarly to the Wind Slabs, shooting cracks or whumpfing collapses are red flag signs that the snowpack is unhappy. If you notice any of these signs, a poor bond, or blocks of snow failing easily during your tests, avoid slopes over 35 degrees.

    (2/5/2023)

    Example: A shovel tilt test is one of many tests you can use to help identify midstorm instabilities.

    Photo: Susie Glass

Avalanche Discussion

It should be a stormy day around the West South zone and although snowfall may be significant in some areas, the story with this one really is the wind. You should expect to encounter touchy avalanche conditions during the height of the storm, including the possibility of some natural avalanche activity. Slabs may be larger and possibly more reactive on the volcanoes where more snow is expected, but we anticipate that it will be a heads-up day throughout the zone.

On Wednesday, snowmobilers along the 410 corridor reported widespread weak surfaces (surface hoar) on most aspects. Further south along the crest, avalanche professionals near White Pass reported the same, but also noted that a thin sun crust had formed on slopes that see direct sunshine. If those weak surfaces are buried intact, slabs could break in surprising ways by failing above you, spanning long distances, or wrapping around terrain features. On those sunny slopes, the crust could help mute surprising avalanche activity but may present a good sliding surface for avalanches to run on or a different kind of poor bond.

To further complicate matters, we are expecting a slight bump in freezing levels around mid-day that loosely coincides with the frontal passage. With low-density snow already in place from our last storm, this jump in temperatures could allow for some heavier snow to fall and create an upside-down layer before returning to colder and lighter snow in the afternoon. Combined with the significant winds and the possible poor bond mentioned above, you’re going to have plenty of interfaces to check for instabilities before committing to a slope.  

Last week’s storm snow is generally right-side up but still lacks a great bond to the underlying 2/25 interface. While we haven’t seen a lot of avalanches on this layer, we haven’t had much of a slab over it to this point. Thursday could start to change that, and although we suspect that most avalanches will occur in the new snow, slides down to the 2/25 interface are certainly not out of the question.

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