Strong wind, continued snowfall and a rising freezing level are testing our young snowpack. No one knows exactly how this will all play out. Conservative terrain selection is key while the mountains adjust in this time of great change.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
The next storm will bring another shot of snow and wind to the South Columbias late Wednesday into Thursday. Another system is expected Friday night. Each storm will bring a slightly warmer air mass driving the freezing level up the mountainside.WEDNESDAY NIGHT: Freezing level at valley bottom, strong southwest wind, 5 to 10 cm of snow.THURSDAY: Overcast, freezing level around 500 m rising to 1000 m, moderate southwest wind at treeline, strong to extreme southwest wind in the alpine, 8 to 15 cm of snow.FRIDAY: Broken cloud cover clearing to a few clouds in the evening, freezing level beginning around 1500 m potentially rising has high as 2200 m, strong southwest wind at treeline, extreme southwest wind in the alpine, trace of precipitation. 5 to 10 cm of snow/rain at lower elevations on Friday night.SATURDAY: Broken cloud cover giving way to a few clouds in the evening, freezing level holding around 1500 m, strong southwest wind initially, slowing to light wind near sundown, trace of precipitation.
Avalanche Summary
A widespread natural avalanche cycle to size 2 was observed in the adjacent Glacier National Park region on Wednesday.On Tuesday avalanches to size 1.5 were widespread, releasing naturally and with human triggers/control work, running on the December 10th weak layer.
Snowpack Summary
The region picked up 20 to 50 cm of new snow with moderate to strong southwest wind Tuesday into Wednesday. The new snow rests on a buried weak layer (December 10th) that consists of facets, surface hoar, and a crust on solar aspects. Results on this interface are quite variable. It's very touchy in some places and less reactive in others. Lower in the snowpack, a pair of weak layers buried in mid-November are 50 to 90 cm below the surface. These layers present as surface hoar and a suncrust. They are most prevalent at treeline but may be found in sheltered alpine terrain too. While not recently reactive, this storm could push them to their breaking point. The most likely place to see an avalanche failing on this interface would be on south aspects at treeline where the surface hoar formed above a sun crust.At the base of the snowpack is a crust that formed near the end of October. Concern for this layer is dwindling but it may still be worth considering in places such as steep, rocky, alpine terrain, especially where the snowpack is shallow. It would likely take a large trigger such as a cornice fall to produce an avalanche on this layer.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.