Avalanche Forecast

High -

Sunday night: Cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds. Alpine high temperatures around -2.

Monday: A mix of sun and cloud. Light south winds. High temperatures at all elevations around 0.

Tuesday: Cloudy with scattered flurries bringing 5-10 cm of new snow. Light south winds, increasing. Alpine temperatures cooling to around -4.

Wednesday: Mainly cloudy. Light southwest winds. Alpine high temperatures around -5.

Reports from Thursday and Friday included numerous observations of small and quite large (size 1-2.5) storm slabs and wind slabs releasing naturally, with skier traffic, ski cuts, and explosives throughout the region. Activity was represented on all aspects and elevations and crown fractures ranged widely, from 10-70 cm.

No new persistent slab avalanches were observed in the past few days, but this region has been highlighted for recent persistent slab avalanche activity. A number of large natural avalanches up to size 3 were reported on east, southeast and south facing slopes above 2000 m in the Rossland area last Monday with crowns up to 100-150 cm in depth.

In the rest of the region on Monday both natural and explosive controlled avalanches up to size 2.5 were observed on all aspects above 1800 m. Many avalanches failed on the December 27th Surface Hoar and one avalanche on a north/northeast facing slope at 1800 m involved the mid November facets.

Rising temperatures forecast for Monday are likely to increase the reactivity of these persistent weak layers.

Stormy weather over the past several days brought 35 to 65 cm of snow to the region. Each snowfall and interval in between has been characterized by variable wind ranging from moderate to strong and shifting from south to north and back again.

As a result, higher elevations have formed a variable array of old and new, fresh and buried wind slabs across all aspects while sheltered lower elevations have seen mainly increasing depths of low density snow.

With a significant rise in temperature forecast for Monday, concern is increasing for weak layers of surface hoar found around 70 to 130 cm deep. These layers have been active as recently as last Monday and may reach a more widespread tipping point as warming increases slab properties in the snow overlying it. These layers are especially concerning in steep, sheltered, large terrain features and shallow rocky areas.

The base of the snowpack is also weak in parts of the region where it consists of sugary faceted snow around a melt-freeze crust.

• Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
• Avoid freshly wind loaded terrain features.
• Surface hoar distribution is highly variable. Avoid generalizing your observations.
• Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.