There have been a few large persistent slab avalanches recently. These are difficult to predict, so conservative terrain selection is the best management strategy. Look for low-angle, sheltered slopes for the best snow, and the safest riding.
Triggering large avalanches on weaknesses in the lower snowpack remains a possibility. In some areas the concern is weak snow around crusts 60 to 120 cm deep, while in others it's weak snow near the bottom of the snowpack. Human triggering of these layers are most likely in steep, rocky slopes with a shallow or thin to thick snowpack.
Recent storm snow has been blown into wind slabs in leeward terrain at upper elevations.
There was one explosives triggered size 2.5 wind slab avalanche, and one natrual size 3 persistent slab avalanche reported in the region on Thursday. These were both reported on southeast aspects in the alpine.
There was also a size 3 persistent slab avalanche reported on an east aspect at 2400 m in the neighboring Waterton National Park region on Thursday.
There were several natural and explosives triggered avalanches up to size 2.5 reported in the region on Wednesday.
A natural size 3 persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area last Thursday.
These recent avalanches are a prime example of the "low probability; high consequence" scenario that persistent slab problems often create.
FRIDAY NIGHT - Cloudy with clear periods / moderate to strong northwest wind / alpine low temperature near -10
SATURDAY - Cloudy with sunny periods / moderate to strong northwest wind / alpine high temperature near -9
SUNDAY - Cloudy with sunny periods / strong west wind / alpine high temperature near -6
MONDAY - Mainly sunny / light to moderate northwest wind / alpine high temperature near -7
15-30 cm of recent snow has been redistributed by strong winds at upper elevations, forming wind slabs in leeward terrain. The storm brought rain to lower elevations, resulting in a crust that is now on the surface up to about 1800 m.
The lower snowpack consists of decomposing crusts and weak, faceted snow. In the Elk Valley, a decomposing surface hoar layer can be found around one of these crusts 60-120 cm below the surface. Avalanche activity on these layers in the lower snowpack has been sporadic, mostly triggered by large loads such as a wind slab avalanche, or a cornice fall. These deeper weak layers are most likely to be human triggered on steep, rocky slopes with a shallow or thin to thick snowpack.
