Avalanche Forecast

Monday night: Cloudy with flurries bringing 10-20 cm of new snow. Moderate southwest winds.

Tuesday: Cloudy with continuing flurries bringing 15-25 cm of new snow and new snow totals to 25-45 cm, continuing overnight. Moderate southwest winds. Alpine high temperatures around -5.

Wednesday: Cloudy with continuing flurries bringing approximately 5 cm of new snow and 2-day snow totals to 50-70 cm, continuing overnight. Light to moderate southwest winds. Alpine high temperatures around -6.

Thursday:Mainly cloudy with isolated flurries and a trace of new snow. 3-day snow totals of 55-80 cm. Light to moderate southwest winds. Alpine high temperatures around -14.

A large (size 2-2.5) persistent slab was triggered by a skier in the Selkirks near Revelstoke on Sunday. The avalanche occurred just below a convex roll situated above a rocky cliff band at 2300 metres and is suspected to have failed on one of our mid-December surface hoar layers. Its crown fracture was up to 60 cm deep.

Other reports from Saturday and Sunday included a few observations of recent natural and skier-triggered wind slabs reaching size 2.5 (large). One wind slab release managed to trigger a very large (size 3) deep persistent slab on a steep, unsupported slope in the high alpine. Its crown fracture was 3 metres deep. All of the above occurred above 2100 metres.

The spectacularly large and destructive natural avalanche cycle observed during last week's big storm has for the most part ended but persistent slabs have shown continued reactivity to explosives and other large triggers.

Light new snow amounts have begun to bury a mix of large surface hoar reported below treeline into the alpine, or instead a sun crust on many steep sun-exposed aspects.

In exposed areas at higher elevations, recent moderate southwest winds have formed some isolated wind slabs with the 10-30 cm of low density snow we received late last week. Elsewhere this recent snow remains unconsolidated. The 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.

100 to 160 cm of snow is now resting on a widespread layer of large, feathery, surface hoar from mid-December. This layer was the primary failure plane in the large natural avalanche cycle last week. Activity on this interface has tapered off, but there is some concern for loading from forecast snowfall to reinvigorate avalanche activity at this depth.

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.

• Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
• Storm slab size and sensitivity to triggering will likely increase through the day.
• Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.