Avalanche Forecast

A low pressure centre coming from the Gulf of Alaska will bring increasing cloudiness on Tuesday and significant snowfalls starting at night.

Monday night: Clear with cloudy periods, light to moderate westerly winds, low treeline temperatures near -1 C with freezing level at valley bottom.

Tuesday: Increasing cloudiness with snow starting at night, 30 to 35 cm overnight, strong to extreme southwesterly winds, high treeline temperatures near +1 C with freezing level around 1500 m.

Wednesday: Snow, heavy at times, 25 to 35 cm, strong to extreme southwesterly winds, treeline temperatures cooling from 0 C to -3 C with freezing level going down to 500 m by the end of the day.

Thursday: Cloudy with scattered flurries, 5 cm, light to moderate westerly winds, high treeline temperatures near -5 C with freezing level at 300 m.

A natural avalanche cycle occurred during the last weekend's storm. North Shore operators reported numerous small to large (size 1-2) natural, human-triggered, and explosive-triggered avalanches releasing 20-50 cm in the storm snow. With recent storm snow still available for transport and southwesterly winds picking up overnight and during the day, natural and triggered avalanches will be possible in wind-affected areas on Tuesday.

We have concern that a persistent slab problem may extend into the south coast region at upper elevations in the north of region, such as near Sky Pilot. In the neighbouring Sea-to-Sky region, we received reports of large (size 2-3) human-triggered avalanches that released on a persistent weak layer between 1700-1900 m with several smaller sympathetic avalanches that have also released during these events. It may still be possible to trigger very large avalanches in isolated areas in the north of the region on Tuesday.

Last weekend's powerful storm brought 40-70 cm of snow to the mountains. Gradual warming that peaked midday likely created a thin crust over much of the storm snow in areas below 1100 m. Strong south winds will continue to transport the new snow into dense slabs that will be possible to likely to trigger, especially where slabs are poorly bonded to the previous surface. The recent snow sits on a mix of previous surfaces, including preserved powder, a sun-crust on steep south-facing slopes, and surface hoar reported at treeline elevations and below. Stay alert to changing slab conditions as you move into wind-exposed terrain, and monitor the bond of the new snow to the old snow surface.

In the north of the region, a concerning layer of facets (sugary snow) can be found down 90-170cm over a crust that formed in early December. This video, filmed prior to Saturday's storm, provides a valuable visual summary of these conditions. It may be possible to human trigger this persistent slab problem in thinner snowpack areas near ridge tops, where the facets are more developed and where the crust layers are more accessible to the weight of a person or machine. Backcountry travelers near Mt Mulligan on Saturday found this layer down 100 cm after experiencing a whumph. You can find additional details and photos about this persistent slab problem in our forecaster blog. 

Below these crust layers, the snowpack is generally well-settled. Early season hazards such as rocks, stumps, and open creeks remain at lower elevations. 

• Choose conservative terrain and watch for clues of instability.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.