Wind slabs may form in high-elevation leeward terrain if there is dry snow available to blow.
Hard, icy surfaces and numerous early-season hazards may make travel challenging.
If you get above the elevation where the surface crust is covered by new dry snow, swatch for small but reactive wind slabs in leeward terrain.
A notable, very large size 3 avalanche stepped down to a persistent weak layer near Allison Pass. This slide is suspected to have run during the heavy rain that fell on Wednesday. Several wet loose avalanches also occurred, see photo captions for more details.
Looking forward, there is a lull in the weather on Saturday before another atmospheric river brings significant precipitation on Sunday and Monday, where we can expect to see more large avalanches occurring.
Previous heavy rain and high freezing levels during the week formed a widespread crust that likely extends high into alpine. The snow surface may be wet at lower elevations, especially during the warmest parts of the day on Saturday. Above treeline, 5 to 15 cm of new snow may be covering the recent crust. Strong westerly winds likely built wind slabs in leeward terrain.
A crust with facets, formed in early November, is buried around 50 to 100 cm at treeline. This persistent weak layer has been the failure plane of some recent large avalanches in the region.
Total snowpack depths range from 80 to 150 cm deep at treeline, and diminish rapidly below 1500 m.
Friday Night
Cloudy. 5 to 15 mm of precipitation as snow or rain at treeline. 50 km/h west ridgetop wind. Treeline temperature 1 °C. Freezing level 1900 m.
Saturday
Mostly cloudy. 1 to 2 mm of rain at treeline. 50 km/h southwest ridgetop wind. Treeline temperature 6 °C. Freezing level rising to 3000 m.
Sunday
Mostly cloudy. 10 to 20 mm of rain at treeline. 60 km/h southwest ridgetop wind. Treeline temperature 2 °C. Freezing level 2100 m.
Monday
Mostly cloudy. 35 to 50 mm of rain at treeline. 60 km/h southwest ridgetop wind. Treeline temperature 3 °C. Freezing level 2300 m.
More details can be found in the Mountain Weather Forecast.
