Conditions are more complicated than meets the eye. Wind-drifted snow and a buried weak layer warrant a cautious approach and diligent decision making.
Strong southeast winds during the recent storm drifted the new snow into dense slabs on leeward terrain features. These wind slabs may remain possible to human trigger, particularly near ridge-crests and roll-overs.
In the north of the region, a layer of weak facets (sugary snow) can be found down 90-170 cm near a crust that formed in early December. It may be possible to human trigger persistent slabs in thinner areas at upper elevations, such as near ridge tops. The possibility for large remote-triggered avalanches warrants conservative terrain margins.
Sunday night: Clear, no new snow expected, light northeast winds, low treeline temperatures near -5 C, freezing level at valley bottom.
Monday: Sunny, no new snow expected, light northwest winds, high treeline temperatures near -2 C, freezing level around 100 m.
Tuesday: Increasing cloudiness, isolated afternoon flurries with trace accumulations, winds becoming west and increasing to strong, high treeline temperatures near 0 C with a possible above freezing layer between 1000-1100 m.
Wednesday: Overcast, 40-60 mm of precipitation, strong southwest winds, treeline temperatures cooling from 0 C to -2 C, an above freezing layer may form between 1200-1500 m but is forecast to break down and drop to 700 m by end of day.
On Saturday, a natural avalanche cycle occurred during the 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. These MIN reports from Hollyburn Mountain, the Mt Seymour trail, and Brockton Point provide helpful photos and details of the touchy conditions on the Northshore on Saturday. Although natural avalanche activity is tapering, it may still be possible to trigger avalanches in wind-drifted areas on Monday.
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 on Thursday, we received reports of two large (size 2-3) human-triggered avalanches that released on a persistent weak layer between 1700-1900 m on west and southwest aspects. Notably, these avalanches were remote-triggered while party members were traveling uphill. Several small sympathetic avalanches were also thought to have released during these events. It may be possible to trigger very large avalanches in isolated areas in the north of the region on Monday.
Saturday'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 redistributed the new snow into dense slabs that may remain possible 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.
