Wind slabs could step down to deeper persistent weak layers.
Start with conservative terrain and gather information before committing to slopes.
Wind slabs built up during the last storm may remain sensitive to human-triggering. Slabs could step down to deeper layers, resulting in larger than expected avalanches.
A crust / facet layer from mid-November is buried 60 to 100 cm deep. Several recent large to very large avalanches have failed on this layer.
On Thursday, several size 2-2.5 explosive-triggered slabs occurred in the Duffey area. these were suspected to have failed on the mid-November persistent weak layer.
On Tuesday, a deep and large slab (size 2.5-3) was observed on Matier’s East Ridge. (See photo below) This slab was also suspected of having failed on the persistent weak layer.
Around 30 to 50 mm of precipitation fell over the last storm. Freezing levels varied, but a surface crust is likely present up to at least 1800 m.
In the alpine, strong winds scoured windward slopes, while building slabs in leeward and crossloaded terrain.
Several layers, including surface hoar, facets, and a thin crust, can be found 40 to 65 cm below the surface.
A crust with facets, formed in early November, is buried 50 to 100 cm at alpine and treeline elevations. This persistent weak layer has been the failure plane of several recent large avalanches in the region.
Snowpack height averages around 100 cm at treeline and decreases rapidly below 1500 m.
Thursday Night
Mostly cloudy. 1 to 4 cm of snow. 20 km/h west ridgetop wind. Treeline temperature -5 °C. Freezing level 1100 m.
Friday
Cloudy. 2 to 4 cm of snow. 30 km/h west ridgetop wind. Treeline temperature -2 °C. Freezing level 1500 m.
Saturday
Mostly cloudy. 1 to 5 mm of precipitation as snow or rain at treeline. 30 km/h southwest ridgetop wind. Treeline temperature 0 °C. Freezing level 1700 m.
Sunday
Mostly cloudy. 5 to 15 mm of rain at treeline. 30 km/h south ridgetop wind. Treeline temperature 1 °C. Freezing level 1900 m.
More details can be found in the Mountain Weather Forecast.
