Avalanche Forecast
Issued: Apr 13th, 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
Large persistent slab avalanches continue to be triggered by riders this past week.
Conservative terrain selection is critical, choose only well-supported, low-consequence lines.
Summary
Confidence
Avalanche Summary
Two persistent slab avalanches occurred on Friday. One was a size 2.5 and it was triggered naturally by the impact of the sun. It started at an elevation of 1500 m and failed at a depth of 40 cm. The second avalanche was a skier accidentally and it reached a size 2. Two people were involved in it but remained on the surface. It happened in an alpine feature and slid on a surface hoar/facet layer that was 40 to 50 cm down.
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 of the alpine.
Two additional skier-triggered size 2-2.5 persistent 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.
Snowpack Summary
By Friday morning 20-30 cm will sit on the storm snow from this past weekend which brought 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
Thursday Night
Mostly cloudy with isolated flurries; 5-10 cm / 30 km/h southwest ridgetop wind / Temperature at treeline around -4 C / Freezing level 800 m
Friday
Mix of sun and cloud with flurries; 2-6 cm / 40 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1000 m
Saturday
Snow; 20-30 cm / 45 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1100 m
Sunday
A mix of sun and cloud / 2 cm / 25-30 km/h southeast wind / Temperature at treeline 0 C
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.
- Be carefull around freshly wind loaded features.
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 14th, 2023 4:00PM
