Avalanche Forecast
Issued: Apr 18th, 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.
swerner,
Avalanche Canada
Fresh and reactive wind slabs may build Wednesday at treeline and above.
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
Avalanche Summary
On Monday, the far reaches north and south of the forecast region saw several explosive triggered avalanches up to size 2.5. In the north, these avalanches are reported as persistent slabs, and in the south storm and wet slabs. There have been no recent avalanche reports from the central regional locations (Terrace area etc.)
Two persistent slab avalanches were reported northwest of Terrace last Wednesday (April 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.
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 and possibly at treeline.
The primary concern is 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 is 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
Tuesday Night
Partly cloudy with some clear periods. Trace of new snow. Ridgetop winds 20-30 km/h from the southwest. Treeline temperatures near -4 and freezing level at valley bottom.
Wednesday
Cloudy with snow 5-10 cm. Ridgetop wind 15-30 km/h from the south. Treeline temperatures near 0 C and freezing level 1300 m.
Thursday
Mix of sun and cloud. Ridgtop wind 20 gusting to 45 km/h from the southeast. Treeline temperatures near +1 C with freezing levels near 1200 m.
Friday
Cloudy with new snow 3-10 cm. Ridgetop wind 15-35 km/h from the southeast. Treeline temperatures near +2 C with freezing levels near 1300 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Cornice failure may trigger large 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
Fresh wind slabs may be reactive to human triggers on leeward aspects in the alpine.
Aspects: North, North East, East, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 19th, 2023 4:00PM
