Avalanche Forecast

During the storm last Wednesday, a very large size 3 avalanche stepped down to a persistent weak layer near Allison Pass. Several wet loose avalanches also occurred, see photo captions for more details.

Looking forward, as another atmospheric river brings significant precipitation on Sunday night and Monday, we can expect to see more large avalanches occurring.

Previous heavy rain and high freezing levels formed a widespread crust that extends into the alpine. The snow surface may be wet from rain at lower elevations.

In the alpine, up to 20 cm of recent snow may be forming wind slabs in leeward north through east-facing terrain. Freezing levels are uncertain, but the rain/snow line is expected to be around 1700 m on Sunday.

A crust with facets, formed in early November, is buried between 50 to 100 cm at treeline. This persistent weak layer has caused some recent large avalanches in the region.

Total snowpack depths range from 80 to 140 cm deep at treeline, and diminish rapidly below 1500 m.

Saturday Night
Mostly cloudy. 2 to 10 mm of rain at treeline. 50 km/h southwest ridgetop wind. Treeline temperature 6 °C. Freezing level 2700 m falling to 2100 m.

Sunday
Cloudy. 2 to 5 mm of precipitation as snow or rain at treeline. 50 km/h southwest ridgetop wind. Treeline temperature 2 °C. Freezing level 2000 m.

Monday
Cloudy. 50 to 75 mm of rain at treeline. 60 km/h southwest ridgetop wind. Treeline temperature 3 °C. Freezing level 2500 m.

Tuesday
Cloudy. 20 to 35 cm of snow at treeline. 50 km/h southwest ridgetop wind. Treeline temperature -1 °C. Freezing level 1500 m.

More details can be found in the Mountain Weather Forecast.

• Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
• Wind slabs are most reactive during their formation.
• Avalanche activity is unlikely when a thick melt-freeze crust is present on the snow surface.