Avalanche Forecast
Issued: Mar 20th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Deep Persistent Slabs and Cornices.
rbuhler,
Avalanche Canada
Wind slabs may still be reactive in exposed terrain at higher elevations.
Human triggering of the lingering deep persistent layer remains a concern in thin snowpack areas and very large avalanches remain possible in isolated areas.
Summary
Confidence
Avalanche Summary
On Sunday, natural size 1 loose wet avalanches were observed from steep rocky terrain on solar aspects.
In the northern Purcells on Sunday, several 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 the 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
Monday Night
Clear, winds northeast 20-30 km/h, treeline low around -12 °C.
Tuesday
Sunny, winds northeast 10-20 km/h, freezing level reaching around 1700 m.
Wednesday
Sunny, winds northeast 15-30 km/h, freezing level reaching around 2100 m.
Thursday
Mainly sunny, winds southwest 15-30 km/h, freezing level reaching around 1800 m.
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
Wind Slabs
The storm snow from last week had been redistributed by southwest winds forming wind slabs. The wind has recently shifted to the northeast and may be forming new slabs where there is still loose surface snow available for transportation. Wind slabs should currently be expected on all aspects in wind-exposed terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
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 21st, 2023 4:00PM
