South Columbia

Another bout of strong winds over Thursday night should refresh surface instabilities in exposed terrain. Seek out sheltered snow but keep your guard up around steep pockets where storm snow may be settling over a fragile layer of surface hoar or a slippery crust.

Thursday night: Increasing cloud. Moderate to strong southwest winds. Mild temperature inversion with warm air aloft, breaking down with the arrival of a cold front in the morning.

Friday: Cloudy with scattered flurries bringing up to 5 cm of new snow. Light to moderate south winds shifting west and easing over the day. Alpine high temperatures falling from around -5 over the day, even as freezing levels rise to about 900 metres.

Saturday: Mainly cloudy. Light variable winds. Alpine high temperatures around -7.

Sunday: Cloudy with scattered flurries continuing from the overnight period and 10-15 cm of new snow. Moderate southwest winds. Alpine high temperatures around -6 with freezing levels rising to about 900 metres.

An extensive natural avalanche cycle occurred over Tuesday night and through the day on Wednesday as around 40 cm of new snow blanketed the region on Tuesday and was subsequently redistributed by strong winds. 

Early observations show many storm and wind slab releases generally in the size 1.5-2.5 range with several reaching up to size 3. In the Trans-Canada corridor, a size 4 (VERY LARGE) avalanche ran on Mt. Laurie. Persistent slab releases have not figured too prominently in reports, but observations are still limited and the few that have been reported are notable. Check out this MIN from the Gorge area for an example of the isolated deep releases we're concerned about.

Looking forward to Friday, it remains a very good idea to give newly formed wind slabs a wide berth as you approach wind affected terrain, and to remain suspicious of steeper sheltered slopes where new snow may have slabbed up over a layer of surface hoar or crust. Using small test slopes to investigate the bond of new snow is a good plan, but be cautious about extending your observations to more committing terrain.

30-40 cm of new snow fell during Tuesday's storm. Varying reports describe either a thin graupel or rain crust layer may be present under about 20 cm of wind redistributed snow below about 1900 metres. Collectively, this layered storm snow buried wind affected surfaces at upper elevations, as well as surface hoar in wind sheltered areas and a thin crust on solar aspects. 

The new snow will take time to form a bond with these previous surfaces, particularly in spots harbouring surface hoar or crust. In exposed areas, elevated winds have been redistributing new snow into reactive wind slabs and adding to cornices. 

A couple of persistent weak layers exist in the upper to mid snowpack:

• The upper layer, now found an estimated 70-120 cm deep, is a spotty layer of surface hoar at treeline and below. 
• The lower layer, now likely closer to 120-190 cm deep, is widespread and may present as decomposing surface hoar and/or a crust.

Avalanche activity on these layers has been dwindling since last week and snowpack tests results have generally indicated the weak layers are gaining strength. Given their age (particularly the deeper layer) and the testing load brought by Tuesday's storm, the outlook is good for these layers to finally become dormant as our current surface instabilities diminish.

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Use small low consequence slopes to test the bond of the new snow.