Avalanche Forecast

Thursday night: Increasing cloud. Strong to extreme 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 about 5 cm of new snow. Light to moderate southwest winds, easing over the day. Alpine high temperatures around -7 and falling over the day, even as freezing levels rise to 1000 metres.

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

Sunday: Cloudy with scattered flurries continuing from the overnight period and 10-15 cm of new snow. Light to moderate southwest winds shifting west. Alpine high temperatures around -7 with freezing levels rising to 1000 metres.

An extensive natural avalanche cycle occurred over Tuesday night and through the day on Wednesday as up to 70 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. Observations are still limited, but with somewhat clearer skies on Thursday it's expected we'll hear of a few more size 3 to 4 releases by the end of the day.

Persistent slab releases have not figured too prominently in reports thus far, 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.

An impressive 30-70 cm of new snow fell in the region 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 80-140 cm down, is a spotty layer of surface hoar at treeline and below. 
• The lower layer, now likely around 110-200 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 that they 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.