Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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

Dangerous avalanche conditions are expected on the volcanoes and the southern half of the West South zone. If you find more than a foot of new snow, start by choosing simple terrain while looking for red-flag signs of instability, using test slopes, and gaining information about how the storm snow has stacked up. In areas with lower storm totals, keep an eye out for wind-loaded features where you’re more likely to trigger a slab.

Avalanche problems

  • Storm Slabs

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

    Snowfall is forecasted to continue throughout Friday night and into Saturday morning in the West South zone. Higher accumulations are expected on the volcanoes where storm totals are already deeper. If you’re in an area where there’s more than a foot of new snow, start thinking about slab avalanches on all steep slopes. You can use small test slopes or quick hand pits as you travel to see how the storm snow has bonded to underlying surfaces, if there are interstorm layers of concern, or if it is upside-down (heavy snow over weak snow). You may see it failing easily in blocks or notice cracking of the surface indicating a potential problem. If you notice these signs or get concerning results with your quick tests, avoid all slopes over 35 degrees.

    Of course, in wind-loaded areas slabs will be thicker and potentially more reactive. This is especially true on specific features such as the lee side of ridgelines or in confined gullies. It is applicable throughout the zone regardless of the amount of new snowfall.

    (3/21/2023)

    Example: Using a small test slope produced shallow slabs indicating a poor bond to the underlying surface.

    Photo: Dallas Glass

Avalanche Discussion

After a week of weather reflective of the springtime calendar, the West South is now in the midst of a more winter-like storm. As alluded to above, the storm has been hitting the volcanoes and southern half of the zone hard for the past few days. As of Friday evening, roughly 1.5 feet of snow has fallen on the volcanoes and White Pass. In areas further north and near the crest such as Crystal Mountain, closer to 5 inches of new snow has fallen. We could squeeze out another 5 or so inches by daybreak on Saturday.

You’ll likely encounter the most dangerous avalanche conditions first thing in the morning as this storm is wrapping up and the snowpack continues to adjust to the new load. As the day wears on, you may find that hazard transitions towards more specific terrain features or is more likely on wind-loaded slopes. On Friday, avalanche professionals in the Crystal area reported low-density snow overlaying a crust on most aspects. This resulted in triggering loose avalanches (sluffs) running at the base of the storm snow on steeper slopes. Periods of graupel were also reported which could become a layer of interest on Saturday.

Prior to the storm, mostly warm and sunny weather impacted the zone for the majority of the week. A surface crust formed on most aspects and elevations. The caveat is high-elevation northerly terrain where dry soft snow survived and possibly faceted (weakened) during this spell. Both of these surfaces could aid in avalanches failing on Saturday, so be sure to check the bond (3/22 interface) throughout your travels. All avalanche activity is suspected to occur at or above this interface throughout the zone.

As the storm winds down and becomes more showery, don’t be surprised to see a sun break or two. This could result in rollerballs or even a few Wet Loose avalanches on steep sun-exposed slopes.

Regions covered