Avalanche Forecast

Moderate - Uncertainty is due to the limited number of field observations.

Saturday night: Cloudy with flurries bringing 5-10 cm of new snow. Moderate southwest winds.

Sunday: Cloudy with continuing flurries bringing another 5-10 cm of new snow, easing over the day. Light to moderate southwest winds (potentially strong in the alpine) shifting west. Alpine high temperatures around -8 with freezing levels rising to 1000 metres.

Monday: Mainly cloudy. Light west winds shifting northwest. Alpine high temperatures around -10.

Tuesday: Cloudy scattered flurries developing late in the day and bringing about 5 cm of new snow by morning. Light to moderate southwest winds (potentially strong in the alpine) increasing over the day. Alpine high temperatures around -7.

An extensive natural avalanche cycle occurred over the midweek as up to 70 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 thus far, but 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 Sunday, it's worth continuing to give 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. Using small test slopes to investigate the bond of recent snow is a good plan, but be cautious about extending your observations to more committing terrain. 

Note that a bit of forecast new snow will add to (and obscure) our wind slab problem, while adding just a bit more load to our buried surface hoar.

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. 

Since the storm, the surface has split into a mixed bag of wind-affected snow in exposed areas, sun crust on sun-exposed slopes, rime crust on all aspects around treeline (possibly not widespread), and a more widespread thin melt-freeze crust below around 1700 metres, which becomes thick and supportive, capping the snowpack at around 1400 metres and below.

Collectively, this varied layer of storm snow is settling over wind affected surfaces at upper elevations as well as surface hoar in wind sheltered areas and a thin crust on solar aspects. In most places, the storm snow seems to be 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 thick surface crust exists and below more wind-affected elevations.

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

• The upper layer (from late December), now about 100-140 cm down, is a spotty layer of surface hoar at treeline and below. 
• The lower layer (from early December), now around 150-200 cm deep, is widespread and now mostly presents as a crust/facet combination.

Aside from last week's storm producing isolated releases on these deeper layers (see the avalanche summary for details), avalanche activity at these depths has been on a downward trend for a couple of weeks, with snowpack tests giving increasingly resistant results. The lower layer is now largely unreactive, but remains a prominent snowpack feature.

• 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.