A big, heavy storm slab has plopped down on our snowpack, the remnants of the recent storm passage. Incoming warm air aloft will keep Danger levels elevated until things cool off.
Choose conservative terrain and avoid overhead hazards, especially if/when the sun comes out. Solar slopes will shed this warm mass quickly with sun!
A persistent weak layer is buried 90-130cm deep. This persistent weak layer is made up of surface hoar at treeline and below. On solar aspects in the alpine and treeline this PWL is a suncrust. Storm slabs could step down to these layers, magnifying the avalanche size.
Up to 60cm of snow, accompanied by strong winds and mild temperatures, created a reactive storm slab. Expect this storm slab to be failing naturally if the sun comes out (ie Frequent Flyer in the Connaught drainage). They will be sensitive to human triggering.
Artillery control in Rogers Pass overnight produced many avalanches from sz 2.5 to 3.5. Natural avalanches before control commenced were running to valley bottom in the Tupper/Macdonald corridor. Natural avalanche activity has decreased with the storm passage.
Ski operations neighbouring Rogers Pass report storm slabs being triggered both naturally and by humans to sz 2.
To summarize the snowpack, we have a heavy, warm, widespread storm slab perched atop a well-settled mid to lower snowpack.
Deeper in the snowpack lingers the Jan 1 persistent weak layer (PWL), buried 90-130cm. The PWL varies in character depending on elevation and aspect. Treeline and below, the PWL is a layer of surface hoar in sheltered areas. Above Treeline and into the Alpine, the PWL is a crust on solar slopes.
The main storyline to follow Wed is the high freezing levels.
Tonight: Mainly cloudy. Alp low 0°C. Winds SW 25km/h. Freezing level (FZL) 1600m
Wed Mainly cloudy with sunny periods. Alp high 3°C with a weak inversion. Winds SW 30-40km/h. FZL 1600-2600m
Thurs Cloudy with sunny periods. Alp high -3°C. Winds NW 15-25km/h. FZL 1000m.
Fri Sunny, Alp high 0°C. Winds light to 20km/h. FZL 1600m. Alpine temp inversion.
