Avalanche Forecast

Wednesday night: Cloudy with continuing snowfall finishing with approximately 5-10 cm of new snow. Light to moderate southwest winds shifting to northwest.

Thursday: A mix of sun and cloud with 3-day snow totals of 45-70 cm and flurries beginning again overnight. Light to moderate west winds easing over the day. Alpine high temperatures around -14.

Friday: Cloudy with continuing snowfall bringing 15-25 cm of new snow, totaling 25-40 cm including overnight accumulations, easing overnight. Moderate south winds, becoming strong at ridgetop. Alpine high temperatures around -3 with freezing levels rising to 1500 metres.

Saturday: Mainly cloudy with scattered flurries bringing 5-10 cm of new snow. Light to moderate southwest winds. Alpine high temperatures around -8.

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 45-70 cm are expected to accumulate on the surface by Thursday morning. The new snow has buried large surface hoar reported below treeline into the alpine. This new interface may present instead as a sun crust on many steep sun-exposed aspects.

The new snow adds to 10-30 cm of storm snow from last week. The (December 27) interface below this older snow 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.

110 to 180 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.

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