Avalanche Forecast
Issued: Mar 15th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Storm slabs are expected to remain reactive to human-triggering in wind-loaded terrain or where slabs are sitting on a weak layer of surface hoar or a sun crust.
Start on smaller terrain features and gather information before committing to bigger terrain.
Summary
Confidence
Weather Forecast
A series of frontal systems coming in off the coast will bring light precipitation throughout the week.
Tuesday Overnight: Mainly cloudy, light precipitation. Localized areas up to 15 cm accumulation. Moderate to strong southwesterly winds. Freezing level dropping to 1000 m.
Wednesday: Partially cloudy, light precipitation. Light to moderate westerly winds. Freezing level rising to 1500 m.
Thursday: Mainly cloudy, light precipitation. Localized areas up to 10 cm accumulation. Moderate to strong southwesterly winds. Freezing level 1500 m.
Friday: Mainly cloudy, light precipitation. Moderate to strong southwesterly winds. Freezing level rising to 1500 m.
Avalanche Summary
On Monday, numerous natural and skier-triggered storm slabs were reported throughout the region. These slabs were most reactive in wind-loaded terrain or where they overlie a weak layer of surface hoar or a crust.
Numerous natural and skier-triggered storm slab avalanches up to size 2 were reported over the weekend.
A large skier-triggered avalanche was reported on Sunday to the west of the Monashees. This avalanche occurred on a convex roll below treeline and is suspected to have failed on a persistent weak layer in the upper snowpack. The full report can be seen here.
Several very large human triggered persistent slab avalanches up to size 3 were reported a week ago. They occurred primarily in the Valhalla, Goat, and Kokanee Ranges. Since then these deeper layers have not produced any avalanches, but continue to produce sudden results in tests. We would be cautious of smaller avalanches or cornice failures stepping down to these layers, or during periods when the snowpack is being tested with new load, solar radiation, or significant warming. This MCR (mountain conditions report) from last week in the Valkyr Range echos the uncertainty and complexity surrounding these weak layers.
Snowpack Summary
Continued light precipitation will add to 20-50 cm of recent settling storm snow. In the alpine and treeline, southwest winds have created deeper deposits of slab in lee areas. Storm snow tapers rapidly below treeline, where moist snow or a melt-freeze crust can be expected from rain and warm temperatures.
This new snow is sitting on various surfaces, including hard wind-affected snow, sun crusts on southerly slopes, and surface hoar on shady or sheltered slopes.
The late February persistent weak layer combination of crust, facets and surface hoar is down 40-50 cm. Reports suggest this layer is becoming less reactive in most areas but remains a concern with warming temperatures and additional load on the snowpack.
Two additional persistent weak layers from late January and mid-February are down 80-120 cm. They both consist of surface hoar and/or melt-freeze crusts. Recent trends indicate these layers are gaining strength.
The most recent human-triggered avalanches on these layers were in the southern Selkirks around the Valhalla, Kokanee, and Goat Ranges over the weekend of March 5-6th.
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Be especially cautious as you transition into wind affected terrain.
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
Problems
Storm Slabs
30-50 cm of recent snow and moderate southwest winds formed fresh storm slabs that have been most reactive in wind-affected terrain; especially where slabs are sitting on a weak layer of surface hoar or a sun crust.
In steep sheltered terrain, small dry-loose sluffs may be reactive to human-triggering. Avoid terrain traps, such as gullies, where the consequences of a small avalanche could be serious.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
The problem is most likely found in the southern part of the Selkirks (e.g. Valhalla, Valkyr, Goat, and Kokanee ranges). Persistent weak layers of facet/crust or surface hoar can be found 50 to 150 cm deep. These layers may be quite stubborn to human triggering but would produce large and surprising avalanches.
Extra caution should be taken when the snowpack is tested with new snow/rain, strong solar radiation, or significant warming.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 16th, 2022 4:00PM
