Avalanche danger will rise through the day as new snow and wind form fresh, reactive slabs. If you see more than 25 cm of new snow, treat avalanche danger as HIGH.
Potential exists for storm slab avalanches to step down to buried weak layers, resulting in very large avalanches.
A persistent slab problem formed by a crust down 70-150 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin-to-thick snowpack. Smaller storm slabs or wind slabs have the potential to step down to a deeper weak layer.
New snow and wind are forming fresh, reactive storm slabs. New and recent snow may overlie a weak interface which could result in deeper and touchier than expected storm slabs.
Enhanced snowfall amounts expected for ranges in the southwest of the region.
Thursday night: Snowfall 5-10 cm for most areas. Strong SW wind. Treeline high around -10 °C.
Friday: Snowfall 5-10 cm for most areas. Strong SW wind. Treeline high around -7 °C.
Saturday: Light snowfall up to 5 cm. Moderate to strong SW wind. Treeline high around -8 °C.
Sunday: A mix of sun and cloud. Moderate SW wind shifting NW. Treeline high around -4 °C.
On Wednesday, evidence of a natural storm slab avalanche cycle size 1-2 was observed, likely having run during the storm earlier in the week. Wind slabs continued to be reactive near Invermere into Tuesday, up to size 2. By Wednesday, avalanche activity was predominantly loose dry entraining mass to size 1.5-2.
On Tuesday just east of the region in the Rockies near Invermere, a size 3.5 (very large) persistent slab avalanche was triggered remotely by a skier on an alpine ridgetop. The resulting crown was 2-3 m deep and the avalanche ran about 1 km to the valley bottom. More details in this MIN report. This and other notable persistent slab avalanches in neighboring regions feature in our latest blog, Photos of recent persistent slab avalanches in the southern interior.
10-20 cm of new snow is forecast to fall in most areas by the end of Friday. Strong winds will likely load new snow into leeward terrain features at upper elevations. An accumulated total of 40-60 cm of new and recent snow now sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar up to 3 mm in sheltered areas.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 70-150 cm. Activity on this layer has been sporadic. It has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.
