Heavy snowfall and wind will build reactive storm slabs. Choose sheltered, low-angle terrain away from any overhead hazards.
A layer of weak facets (sugary snow) can be found down 100-150 cm over a crust that formed in early December. There have been reports of natural and human-triggered avalanches on this layer during the last storm in areas where the overlying slab is shallower.
Storm slabs are expected to develop as snowfall accumulates through Saturday. Slabs will be more reactive on leeward (wind-loaded) slopes where deposits are deeper and stiffer. Be mindful of loose-dry sluffing in steeper wind-sheltered terrain.
Light to heavy snowfall is expected across southern BC Friday night through Sunday. An easterly arctic front meeting a southwesterly flow will produce enhanced snowfall where this clash occurs; a band of heavy snowfall is forecasted from Waterton, through Fernie, and into the western South Rockies.
Friday night: Snow, 10-20 cm overnight. Southwest wind, gusting to 50 km/hr. Treeline temperatures near -12 and freezing level at valley bottom. Temperatures continue to drop overnight.
Saturday: Ongoing flurries, another 10-15 cm accompanied by moderate southwest wind. Treeline temperatures near -13 and freezing levels at the valley bottom.
Sunday: Cloudy with scattered flurries, 5-10 cm. Light winds from the southwest and colder temperatures at -17.
Monday: Mix of sun, cloud, and isolated flurries. Calm winds and cold temperatures with a high of -19.
On Thursday, skiers and machines triggered storm slab avalanches to size 2, explosives triggered slab avalanches to size 3. Poor visibility prevented good alpine observations.
Operators have reported that re-loaded bed surfaces (areas that have already avalanched this season) have become reactive with new loads, while deeper snowpack areas that did not previously avalanche remain dormant, furthering the complexity of dealing with a persistent weak layer.
Ongoing snowfall over the weekend will add to 30-50 cm of recent storm snow. The new snow buried a surface hoar interface and pockets of old wind slab. Low-density storm snow exists in wind-sheltered areas.
Below the new snow exists a well-consolidated upper snowpack which overlies a substantial crust that formed in early December. This crust is approximately 90-150 cm below the surface, 20 cm thick on average, and is present across all aspects to at least 2400 m. A layer of weak facets (sugary snow) has been reported above this crust. Snowpack tests are generally showing hard results on this interface.
The lower snowpack consists of a variety of early-season crusts and mainly moist snow. Snowpack depths range from 100-200 cm at treeline elevations and taper quickly below 1800 m.
