Avalanche Forecast
Regions: South Rockies.
With new snow and strong to extreme wind, widespread storm slabs are expected. This new snow will also add load to persistent weak layers in the snowpack. Choose conservative terrain and avoid overhead hazard.
Confidence
Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the limited number of field observations.
Weather Forecast
TUESDAY NIGHT - Snow, 10-20 cm / southwest wind, 40-80 km/h / alpine low temperature near -2 / freezing level 2000 m
WEDNESDAY - Flurries, 5-10 cm / southwest wind, 60-80 km/h / alpine high temperature near -2 / freezing level 1500 m
THURSDAY - Mainly sunny / light northwest wind / alpine high temperature near -8Â
FRIDAY - A mix of sun and cloud / light to moderate southwest wind / alpine high temperature near -5
Avalanche Summary
Fresh storm slabs are expected to be widespread and easy to trigger. Natural avalanche activity is also possible, and the likelihood of this will increase throughout the day as the new snow piles up.
A large (size three) cornice triggered persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area on Thursday. This avalanche failed on weak facets overlying a hard crust deep in the snowpack and is an example of the "low probability; high consequence" scenario that persistent slab problems often create. View the MIN report HERE.
Snowpack Summary
With 15-30 cm of new snow and strong to extreme southwest wind expected between Tuesday night and Wednesday afternoon, storm slabs are anticipated to be widespread and reactive.
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.
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Avalanche Problems
Storm Slabs
Fresh storm slabs will likely be widespread and easy to trigger.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible - Likely
Expected Size: 1 - 2
Persistent Slabs
Triggering large avalanches on weaknesses in the lower snowpack remains a possibility, especially with new snow adding load to these weak layers. 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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3