Storm slabs remain reactive with the greatest hazard in wind loaded terrain. Choose conservative terrain while the snowpack gains strength.
Storm slabs remain reactive to human triggers, the snowpack will take time to gain strength from a significant new load of snow, rain and wind. Investigate the bond between the storm slab and old snow surface.
Use caution around wind effected terrain features and lee (wind loaded) slopes.
Storm slabs in the Toby Creek drainage may sit on a reactive surface hoar layer below 1900m.
A layer of facets exists at the base of the snowpack. These very weak crystals continue to be a concern, especially as new load is added to the snowpack. Deep persistent slabs have a lower probability of triggering, but a much higher consequence.
Smaller avalanches have the potential to step down to these deeper weak layers, producing very large and destructive avalanches.
After a final wave of moisture Wednesday night, freezing levels drop and cloudy skies return. The next round of precipitation arrives Saturday morning.
WEDNESDAY NIGHT: Strong, easing to moderate southwest winds. Freezing levels drop to 1500m by Thursday morning. 10cm overnight, favouring the north.
THURSDAY: Clearing skies as flurries taper off. Winds ease to moderate westerlies. Temperatures drop, with freezing levels falling to valley bottom in the afternoon. Alpine highs near -8.
FRIDAY: Cold and clear with alpine highs around -10. Freezing levels stay below 1000m with light to moderate westerly winds.
SATURDAY: Light accumulations with strong southwesterly winds. Freezing levels remain below 1500m.
Observations over the last week show consistent direct-action avalanche cycles, where new snowfall and winds produce natural avalanches throughout and immediately following the storm.
On Tuesday November 30th, several naturally triggered size 1 storm slab avalanches were observed in north facing treeline and alpine terrain near Invermere. Multiple size 1 storm slabs were explosively triggered in the same area, in wind loaded north facing terrain features.
Over the last 3 days, numerous natural and explosive triggered storm slabs have been observed up to size 2 in the north and central Purcells with the recent heavy snowfall. Of note, several avalanches in the Toby Creek drainage are thought to have failed on a late November surface hoar layer. This is believed to be widespread in the Toby Creek drainage area above 1600m, however data is sparse this early in the season and this layer may extend to other areas.
Up to 80mm of heavy snowfall and mixed precipitation over the last week have added a significant new load to the snowpack. Strong southwesterly winds have redistributed this load to create deeper deposits in lee features at treeline and above.
A surface hoar layer has been observed down 40 to 50cm in the Toby Creek drainage in wind sheltered features. Recent avalanche observations have shown this layer to be reactive. The mid-November rain crust exists throughout the region below 1900m, around 60-100cm down in the snowpack.
The lower snowpack holds several early season crusts. A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer continues to produce results on snowpack tests, and will likely continue to be an issue.
Average snowpack depth at treeline is 100cm - 180cm, with the deepest snowpack found near the Bugaboos. Elevated freezing levels over the past week have created moist snow at lower elevations.
