Avalanche Forecast
Issued: Mar 21st, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Wind Slabs and Cornices.
zryan,
Avalanche Canada
Human-triggering large slab avalanches remains possible in steep, rocky, and/or wind-affected terrain.
Start and finish your day early and plan to be well away from sun exposed slopes and overhead hazard before the warmest part of the day.
Summary
Confidence
Moderate
Avalanche Summary
On Monday, a size 1 natural cornice failure occurred in the St Mary's east of Kaslo. The cornice dropped onto a steep slope and gouged down to the weak facets at the base of the snowpack.
On Sunday, natural size 1 loose wet avalanches were observed from steep rocky terrain on solar aspects.
In the northern Purcells on Sunday, several large natural deep persistent avalanches were observed and in the nearby Pedley Pass, this MIN report describes what was expected to have been a remotely triggered slab that failed down 80 cm. While activity may have started to taper off on the deeper layers in this region, nearby avalanches are a reminder that the layers are likely still reactive in some locations in the region, especially thin, rocky areas in the alpine.
On Friday afternoon, a snowmobile triggered a large persistent slab avalanche (size 2.5) in the south Purcells. The avalanche occurred in burnt forested terrain on a south aspect at 2200 m. It failed on a 50-100 cm deep layer that is suspected to be a sun crust buried in February.
Snowpack Summary
The snow surface consists of a sun crust on solar aspects, small facets and surface hoar on shaded and wind-sheltered slopes, and wind-affected surfaces in exposed terrain. The wind direction recently shifted from the southwest to the northeast so wind slabs are possible on all aspects in exposed terrain.
An interface buried around March 11 sits down 30-40 cm and typically consists of a thin sun crust on solar slopes and wind-affected snow in exposed terrain.
In the Purcells around St Mary's, several weak layers from January and February can be found down 50-120 cm. These layers appear to have generally gone dormant but could still be reactive in isolated areas and should be on your radar in the Purcells part of the region.
The lower snowpack is made up of a widespread layer of large, weak basal facets and depth hoar in some areas. This weakness has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.
Weather Summary
Tuesday night
Clear. Alpine temperatures drop to a low of -6 °C. Light variable ridge wind. Freezing level at valley bottom.
Wednesday
Sunny. Alpine temperatures reach a high of 1 °C. Light variable ridge wind. Freezing level rises to 2100 metres.
Thursday
A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -1 °C. Ridge wind 10 to 40 km/h from the southwest. Freezing level rises to 1900 metres.
Friday
Cloudy with sunny periods. Alpine temperatures reach a high of -4 °C. Ridge wind light from the west. Freezing level rises to 1000 metres.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
- Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
Problems
Deep Persistent Slabs
The base of the snowpack remains very weak. Very large human-triggered avalanches are possible at treeline and above. Avoid thin, rocky start zones and shallow areas with variable snowpack depths where you are most likely to trigger this layer. Give careful consideration to the slopes overhead as large avalanches may run well into the runout zone or into lower-angle terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Lingering wind slabs may persist at higher elevations. Winds have recently shifted directions so wind slabs may exist on all aspects in exposed terrain.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Cornices
Cornices may become weak during the heat of the afternoon. Use extra caution when travelling on ridges and avoid slopes with large cornices overhead during the heat of the afternoon.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 22nd, 2023 4:00PM
