Avalanche Forecast

Archived

Dec 10th, 2021–Dec 11th, 2021

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Vancouver Island.

The snowpack needs time to adjust to the rapid, critical load from heavy snow and strong wind. Keep your guard up and stick to simple, low-angle slopes with no overhead hazard to manage these dangerous conditions.

Confidence

Moderate - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.

Weather Forecast

Friday night: Cloudy, 20-40 cm of snow above 1200 m, strong southwest wind, treeline temperatures nearing 0 C overnight and dropping to -5 C, freezing level rising to 1200 m and dropping to 600 m.

Saturday: Cloudy, 5-15 cm of snow above 600 m, strong southwest wind, treeline temperatures near -4 C.

Sunday: Mainly cloudy, 5-15 cm of snow above 600 m, moderate southwest wind, treeline temperatures near -5 C.

Monday: Mix of sun and cloud, isolated flurries with trace accumulations, moderate southeast wind, treeline temperatures near -4 C, freezing level near 700 m.

Avalanche Summary

We expect that natural and human triggered avalanches will release large and run far during the storm.

Snowpack Summary

A potent storm with strong wind is forecast to bring 30-60 cm of new snow to the mountains by the end of Saturday. This will create a widespread, reactive storm slab problem that will be particularly pronounced where the snow is drifted by southwest winds. The snowpack will need time to adjust to this rapid, hefty new load. Closely monitor how the new snow is bonding to the old surface as the cold snow is not expected to bond well to the hard crust.

Storm accumulations are covering a variety of old snow surfaces. These include: two distinct crust layers that formed in early December, wind-affected surfaces at upper elevations, and soft snow preserved in sheltered areas up high. Below the early December crust layers, the snowpack is generally well-settled.

Recent indications of the region's snowpack suggest that snow depths at treeline are around 170 cm and taper dramatically below treeline. Although gradually improving, below treeline elevations are still largely below the threshold for avalanches except for areas near the upper boundary.

Terrain and Travel

Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
Expect slab conditions to change drastically as you move into wind exposed terrain.
Don't let the desire for deep powder pull you into high consequence terrain.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.