Avalanche Forecast

Moderate - Forecast snowfall amounts are uncertain.

Thursday night: Cloudy with continuing snowfall bringing another 15-25 cm of new snow. Moderate to strong southwest winds.

Friday: Mainly cloudy, becoming clear in the evening. Light to moderate southwest or west winds. Treeline high temperatures around -4.

Saturday: Cloudy with increasing flurries bringing 10-20 cm of new snow, increasing overnight. Moderate to strong south winds. Treeline high temperatures reaching 0C by late afternoon as freezing levels climb to with freezing levels climbing to 2000 metres; continuing to rise to 2300 m overnight.

Sunday: Cloudy with easing flurries bringing about 5 cm of new snow, 30-60 cm totals including overnight snowfall. Light to moderate southwest winds. Treeline temperatures dropping from +1 to -2 over the day as freezing levels descend to 1500 metres.

We don't yet have observations from Thursday's storm, but it's safe to say it was an active day for avalanches as moderate to heavy snowfall and extreme winds impacted the region. Looking forward to Friday, the primary concern is likely to be wind slabs, potentially large, perched in leeward pockets at ridgetop and around exposed terrain features. Natural avalanches will likely taper off but human triggering will remain a real concern. 

Reports of weak surface hoar grains found on the snow surface in advance of the storm are another reason to take a cautious approach in your post-storm investigations on Friday. Slabs will be particularly reactive if they formed over preserved surface hoar.

By the end of Thursday's storm, the region will have picked up 30-70 cm of new snow, with heavier accumulations likely favouring the south of the region. Strong to extreme winds accompanied this snowfall. 

The new snow buried mainly wind affected surfaces, however surface hoar was observed in the Whistler area earlier this week. As a result, storm slab reactivity may persist in places where new snow buried these weak grains. A thick crust, breakable at treeline and below, is now likely 40-90 cm deep throughout the region. This crust may be found directly at the new snow interface or even at the surface on windward slopes. In the alpine, another crust is now probably around 130-170 cm deep.

Average snow depths at treeline are now likely closer to 120-190 cm; 250+ cm in the alpine. Snowpack depths decrease dramatically below treeline and may still be below threshold for avalanches in some areas. This is changing with each storm pulse we see. Early season hazards such as rocks, stumps, and creeks are still a concern at these lower elevations.

• Closely monitor how the new snow is bonding to the old surface.
• Start on smaller terrain features and gather information before committing to bigger terrain.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.