Avalanche Forecast
Issued: Apr 17th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Wind Slabs and Loose Wet.
jsmith,
Avalanche Canada
Numerous large persistent slab avalanches have been triggered by riders in the alpine during the past week.
Conservative terrain selection is critical, choose only well-supported, low-consequence lines.
Summary
Confidence
Low
Avalanche Summary
Numerous naturally triggered dry loose and wet loose avalanches up to size 2 occurred on steep, rocky slopes on all aspects on Sunday.
Two persistent slab avalanches were reported northwest of Terrace last Wednesday (12th). 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 last Tuesday (11th). 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.
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
10-20 cm of recent snow and strong southeast wind formed wind slabs that may remain reactive to human triggers in isolated locations in the alpine.
The primary concern are two buried weak layers 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 during the past 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
Monday Night
Partly cloudy / 20 km/h east ridgetop wind / Temperature at treeline around -5 C / Freezing level valley bottom
Tuesday
Mix of sun and cloud with isolated flurries; 0-15 cm / 20 km/h east ridgetop wind / Temperature at treeline around -3 C / Freezing level 1200 m
Wednesday
Mostly sunny / 20 km/h southeast ridgetop wind / Temperature at treeline around -1 C / Freezing level 1400 m
Thursday
Mix of sun and cloud with isolated flurries; 3-10 cm / 20 km/h south 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.
- Cornice failure may trigger large avalanches.
- If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Persistent Slabs
Numerous large persistent slab avalanches have been triggered by riders in the alpine during the past week.
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
Lingering wind slabs may remain reactive to human triggers on lee aspects in the alpine.
Aspects: North, North East, East, South West, West, North West.
Elevations: Alpine.
Likelihood
Expected Size
Loose Wet
Strong solar radiation may trigger wet loose avalanches on steep, sunny slopes.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Apr 18th, 2023 4:00PM
