Avalanche Forecast
Issued: Apr 12th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
jsmith,
Avalanche Canada
Numerous skier triggered, large persistent slab avalanches have been reported in recent days.
Conservative terrain selection is critical, choose only well supported, low consequence lines.
Summary
Confidence
Moderate
Avalanche Summary
A fatal avalanche occurred north of Stewart on Tuesday. It was a skier triggered size 3 persistent slab avalanche that occurred on a northeast aspect in the alpine.
Two additional skier triggered size 2-2.5 persistant slab avalanches were also reported on northerly aspects at treeline and above on Tuesday. The depth of the weak layer was around 60-80 cm.
On Monday, several skier triggered size 2 persistent slabs were reported on a variety of aspects at treeline and above. The slabs were 25-80 cm thick.
Observations are limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.
Snowpack Summary
The recent storm produced 30-60 cm of snow (above 1500 m) and rain below 700 m. At upper elevations, southwest winds formed wind slabs on north-to-east-facing slopes. The recent snow sits over wind-affected surfaces, weak faceted crystals, or a crust on south-facing slopes.
A weak layer buried at the end of March sits 50-90 cm deep in most areas. It includes facets and surface hoar in shaded areas, and a melt-freeze crust elsewhere. Numerous human triggered persistent slab avalanches have occurred on this layer.
The mid and lower snowpack are considered generally strong and well-bonded. In the far northern reaches of the region, basal facets may exist which are currently considered inactive. This layer may become active with abrupt changes to the snowpack, such as rapid loading (heavy snowfall or rain) or prolonged warming.
Weather Summary
Wednesday night
Cloudy with flurries; 3-15 cm / 30 km/h southwest ridgetop wind / Temperature at treeline around -8 C / Freezing level valley bottom
Thursday
Mostly cloudy with isolated flurries; 3-10 cm / 20 km/h southwest ridgetop wind / Temperature at treeline around -5 C / Freezing level 1000 m
Friday
Mix of sun and cloud with isolated flurries; 0-3 cm / 30 km/h southeast ridgetop wind / Temperature at treeline around -4 C / Freezing level 1000 m
Saturday
Snow; 10-20 cm / 40 km/h south ridgetop wind / Temperature at treeline around -4 C / Freezing level 1100 m
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
Problems
Persistent Slabs
Buried layers from late March reached a tipping point and recently became reactive.
The primary concern is a layer of facets and surface hoar buried 50-90 cm on shaded slopes. On other slopes, this layer is a crust with facets above. Avoid steep open slopes capable of producing large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Wind slabs remain reactive to human triggers, especially where they overlie weak facets or a hard crust.
Aspects: North, North East, East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 13th, 2023 4:00PM
