Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Dangerous avalanche conditions are expected to develop on Thursday, particularly on the volcanoes. Anywhere you encounter 6 inches of new snow or wind-loaded features, start thinking about slab avalanches. When in doubt, avoid slopes over 35 degrees.

Avalanche problems

  • Storm Slabs

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

    As snow piles up Wednesday night and Thursday, you could encounter storm slabs at mid and upper elevations. Slabs should be larger on the volcanoes where more snowfall is expected. Use small test slopes and uptrack tests to determine how the new snow is reacting to your weight. Dig down until you hit a crust to see if there are potential points of failure. If you find heavy snow over weaker snow, see shooting cracks, or blocks of snow failing in your tests, default to lower-angled terrain.

    In areas with less than 6 inches of new snow, you should focus on wind-loaded features where you’re more likely to trigger an avalanche. In isolated locations, slabs could break in surprising ways - running on the 12/30 crust or stepping down to deeper layers. See below for more details.

    (12/2/2023)

    A shooting crack on a test slope or uptrack test helps to indicate an unhappy snowpack.

    Photo: Dallas Glass

Avalanche Discussion

On Wednesday, the West South zone received roughly 2-4 inches of new snow accompanied by gusty winds. Snowfall should continue overnight and into Thursday, with precipitation totals focusing on the volcanoes where over an inch of water is expected. 

Crystal Mountain Pro Patrol reported small but sensitive cornices and areas of wind-drifted snow during their morning mitigation work. Later in the day, a few larger pockets of wind-drifted snow were triggered. 

As we roll into a stormy couple of days, there are several interfaces in the upper snowpack to consider. Here’s some information on them, starting with the deepest:

  • 12/22 interface: The deepest layer of concern. It is roughly 1-1.5 feet below the surface. We do not anticipate any avalanches below this crust/facet sandwich and few to occur at it. 
  • 12/25 crust: The next significant crust above the 12/22 complex. This layer has been producing propagating test results in recent days. NWAC and professionals have identified buried surface hoar above this layer.
  • 12/30 crust: Closest easily identifiable crust to the surface. It should be the sliding surface for most avalanches in the coming days. 
  • 1/2 interface: A layer of buried surface hoar may exist an inch or two above the 12/30. Where it exists, avalanches breaking on this layer could span far distances or wrap terrain features. There also may be near-surface facets in this vicinity.

Reported avalanche activity has been limited in previous days, but we anticipate it to slowly climb as we continue to load these layers. That process should begin tomorrow in some areas of the zone. Your most significant concern at lower elevations will continue to be travel hazards.

Regions covered