Avalanche Forecast

High -

Friday night: Cloudy with isolated flurries and a trace of new snow. Light west winds.

Saturday: Mainly cloudy with flurries developing overnight. Light west winds shifting southwest and increasing overnight. Alpine high temperatures around -6.

Sunday: Cloudy with scattered flurries continuing from the overnight period and 10-15 cm of new snow, easing over the day. Light to moderate southwest winds shifting northwest. Alpine high temperatures around -6 with freezing levels rising to about 900 metres.

Monday: Mainly cloudy, diminishing over the day. Light to moderate northwest winds easing over the day. Alpine high temperatures around -8.

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. 

Observations show many storm and wind slab releases, of course during but also following this event, 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. Observations from Friday show a slight transition toward wind slab releases as well as further evidence of the preceding avalanche cycle. Wind slab reports have failed to reveal a predominant aspect, likely owing to recent shifting winds.

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 these MIN reports from the Gorge area and from Mt. MacPherson for an example of the isolated deep releases we're concerned about.

Looking forward to Saturday, it remains a good idea to give recently 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. In exposed areas, recent elevated winds have been redistributing the uppermost storm snow into reactive wind slabs and adding to cornices.

In most places, the storm snow is probably forming a good bond with the previous surface. Exceptions are likely in areas harbouring surface hoar. Think of shaded upper below treeline and lower treeline areas, above where surface crust exists and below more wind-affected elevations.

A couple of persistent weak layers exist in the mid to lower 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.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Use small low consequence slopes to test the bond of the new snow.
• When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.