Avalanche Forecast

Wednesday night: Cloudy with continuing snowfall finishing with approximately 10 cm of new snow. Moderate to strong west winds.

Thursday: Mainly cloudy with 3-day snow totals of 60-110 cm and flurries beginning again overnight. Light to moderate west winds easing over the day. Alpine high temperatures around -10.

Friday: Cloudy with flurries bringing 5-10 cm of new snow, totaling 20-40 cm with overnight accumulations. Flurries easing overnight. Moderate south winds, becoming strong at ridgetop. Alpine high temperatures around -3 with freezing levels rising to 1500 metres by evening.

Saturday: Mainly cloudy with scattered flurries bringing 5-10 cm of new snow. Moderate southwest winds. Alpine high temperatures around -6.

Observations from Tuesday showed storm slabs becoming highly reactive to skier traffic and ski cutting, often producing avalanches to size 2 (large), occasionally to size 3 (very large), even on quite low-angle slopes and with remote triggers. 

With slabs initially ranging from 20-40 cm deep, both our most recent storm interface and the slightly older December 27 surface hoar described in our snowpack summary were likely to be involved in this activity. Isolated reports identify our much deeper mid-December weak layer. The destructive potential of avalanches on these layers has been increasing, with snow accumulation forecast to continue through Wednesday night.

Looking forward, very dangerous avalanche conditions as described above are expected to persist even as snowfall tapers for Thursday.

3-day snow totals of 60-110 cm are expected to accumulate on the surface by Thursday morning. The new snow has buried a mix of large surface hoar from below treeline into the alpine, in places either combined with rime crust or replaced by sun crust on steep sun-exposed aspects.

The new snow adds to 10-30 cm of older storm snow from last week. The (December 27) interface below it may present as a sun crust on steep sun-exposed aspects, as surface hoar in more sheltered lower elevations, or as a more widespread melt-freeze crust below about 1700 metres. In some places it may behave as a primary storm slab interface below our new snow accumulations.

130 to 200 cm of snow is now resting on a widespread layer of large, feathery, surface hoar from mid-December. Activity on this interface has tapered off, but there is concern for the possibility of storm slab releases to step down to this layer.

Another weak layer formed in late November is now over 170 cm deep. Concern for this layer is limited to rocky or variable snowpack depth areas in the alpine where it most likely exists as a combination of facets and crust.

• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Avoid freshly wind loaded terrain features.
• Avoid being on or under sun exposed slopes.