Avalanche Forecast
Issued: Apr 15th, 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 large persistent slab avalanches have been triggered by riders this past week.
Conservative terrain selection is critical, choose only well-supported, low-consequence lines.
Summary
Confidence
Moderate
Avalanche Summary
Numerous naturally triggered small (size 1) loose dry and wind slab avalanches were reported at upper elevations on Friday.
Two persistent slab avalanches were reported northwest of Terrace on Wednesday. A skier triggered size 2 on a north aspect in the alpine and a size 2.5 on an east aspect in the alpine that was triggered by solar radiation. Both failed on a layer of weak facets and/or surface hoar down 40-50 cm.
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 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.
Snowpack Summary
5-20 cm of new snow and strong south wind have formed fresh wind slabs reactive to human triggers on lee features at treeline and above.
Two buried weak layers are down 40-120 cm deep in most areas. They include facets and surface hoar in shaded areas, and a melt-freeze crust elsewhere. Numerous human triggered persistent slab avalanches have occurred on these layers this week.
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
Saturday Night
Mostly cloudy with flurries; 3-10 cm / 20 km/h south ridgetop wind / Temperature at treeline around -5 C / Freezing level valley bottom
Sunday
Mostly cloudy with isolated flurries; 0-5 cm / 20 km/h southeast ridgetop wind / Temperature at treeline around -4 C / Freezing level 1100 m
Monday
Mix of sun and cloud / 10 km/h south ridgetop wind / Temperature at treeline around -4 C / Freezing level 1100 m
Tuesday
Mix of sun and cloud / 10 km/h northwest ridgetop wind / Temperature at treeline around -3 C / Freezing level 1200 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.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Cornice failure may trigger large avalanches.
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
Recent snow and strong south wind have formed fresh wind slabs on lee features at treeline and above.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 16th, 2023 4:00PM
