Purcells

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 northwest winds becoming strong or extreme in the alpine. Mild temperature inversion with warm air aloft continuing into the morning.

Friday: A mix of sun and cloud with isolated flurries. Light to moderate southwest wind (strong to extreme in the alpine) shifting northwest and gradually easing. Alpine high temperatures falling from around -5 under a diminishing temperature inversion with freezing levels rising to about 900 metres.

Saturday: A mix of sun and cloud. Light west winds. Alpine high temperatures around -7.

Sunday: Cloudy with isolated flurries and up to 5 cm of new snow. Light to moderate southwest winds shifting west. Alpine high temperatures around -7 with freezing levels rising to about 900 metres.

Observations of the storm's aftermath in the Golden area on Wednesday showed explosives control yielding many size 2 (large) storm slabs about 40 cm deep, but with a variability in depth that shows good evidence of wind redistribution.

In the Quartz Creek area, a skier triggered a size 2 (large) storm slab on a 35 degree, north-facing slope at 2100 metres, giving a good indication of storm instabilities that certainly didn't require explosives to produce large avalanches. We're expecting more observations of the widespread natural avalanche cycle noted in neighbouring regions to trickle in over the coming days.

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.

15-40 cm of new snow fell in the region during Tuesday's storm. It 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, found 40-60 cm down, is a spotty layer of surface hoar at treeline and below. 
• The lower layer, found 90-140 cm down, is widespread and can present as surface hoar and/or a crust.

Avalanche activity on these layers has dwindled since last week and snowpack tests results have generally indicated the weak layers are slowly gaining strength. Avalanche activity resulting from the storm may shed some light on whether or not they remain a concern.

The lower snowpack is characterized by more crusts, the most notable is a rain crust from early November that is near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

• 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.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.