Avalanche Forecast

A break in the weather is expected on Wednesday before the next system arrives overnight bringing light snowfall for Thursday. 

Tuesday night: Periods of light snowfall 2-4 cm, light to moderate variable wind, treeline temperature dropping to around -24 °C. 

Wednesday: A mix of sun and cloud, light N wind, treeline high around -20 °C. 

Thursday: Periods of light snowfall 3-6 cm, moderate to strong SW wind, treeline high around -12 °C. 

Friday: Periods of light snowfall, moderate to strong SW wind, treeline high around -6 °C. 

On Monday, explosives triggered wind slabs up to size 2 and a ski cut produced a size 1 storm slab. 

On Tuesday just north of the region in the Rockies near Invermere, a remotely triggered size 3.5 persistent slab avalanche was reported at 2300 m on a W aspect. This was triggered from the ridge and the failure started in the early-Dec layer down 120 cm but subsequently stepped down to the basal weakness. The resulting crown was 2-3 m deep and the avalanche ran about 1 km to the valley bottom. While this was not in the South Rockies region, it provides an example of what might be possible with the weak layers deep in the snowpack. 

On last Friday, explosives triggered a size 2.5 wind slab avalanche that stepped down to the persistent slab layer on a SE aspect near treeline. While recent reports of large persistent slab avalanches have been minimal in the region, neighbouring regions including the Lizard-Flathead have seen some concerning avalanches recently including this one on Sunday.

On Wednesday, recently formed storm slabs are expected to remain reactive to human triggering, especially in wind loaded terrain at higher elevations. These new slabs may sit on a weak interface which may result in them persisting longer than normal. The early-Dec persistent slab problem remains a serious concern and the weight of the new snow may have increased the reactivity of these deeper layers. Smaller storm slab avalanches also have the potential to step down to deeper layers resulting in very large avalanches. 

The region typically received 20-30 cm of new snow from the recent storm. This new storm snow buried a highly wind affected snow surface and widespread facets from the recent cold conditions which may create a weak bond with the new snow. The new snowfall was accompanied by moderate to strong winds at higher elevations and the new storm slabs are expected to be most reactive in wind loaded areas in the alpine. 

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now typically down 70-130 cm. In the past week, we have seen explosive triggered activity on this layer as well as snowpack tests that have shown that the layer remains reactive. Neighbouring regions have seen very large avalanches on this layer over the past week. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques. 

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.