Avalanche Forecast

Moderate - Due to the number of field observations

We're looking at clear and cold from Sunday onwards, with overnight lows near -25 Celsius in some locations. Sunday: Clearing in the afternoon but cold. Tree line temperatures around -17C. Winds light to moderate northeasterly.Monday: Sunny with cloudy periods. Tree line temperature around -15C. Winds light northerly.Tuesday: Sunny with cloudy periods. Tree line temperature around -12C. Light winds becoming moderate northerly.

On Thursday we received reports of recent cornice-triggered slab avalanches on high lee (down wind) features in the alpine. See this MIN post for more information. On Wednesday, several avalanches were reported in recent storm snow up to size 2.5. Previously, a very large, widespread natural avalanche cycle up to size 4 was observed around February 10th. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was destroyed. Many of these failed on persistent weak layers mentioned in the snowpack discussion. Although natural avalanche activity on these layers has tapered-off, human triggering of very large avalanches remains a very real possibility.

25-40cm of recent storm snow is settling into a slab in the upper snowpack. Winds have been strong from the north west through south west, creating reactive hard wind slabs (10-15 cm thick) in exposed locations on down wind features. See here for a good video summarizing conditions near Valemount. These accumulations overlie a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects and surface hoar on sheltered slopes.Below the snow surface, several persistent weak layers make up a troublesome snowpack. In the top 1-1.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find at least one of these layers on all aspects and elevations.Deeper in the snowpack (120-200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.