Avalanche Forecast
Issued: Feb 28th, 2020 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Winds are strong and shifting direction as snow accumulates, creating a tricky pattern of wind slabs at upper elevations. Use caution around drifted slopes and convex roll-overs, especially where these slabs may overly a buried weak layer.
Summary
Confidence
Moderate - Uncertainty is due to the track & intensity of the incoming weather system. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
Friday night: Cloudy, 10-15 cm of snow, strong southwest winds switching to northwest, freezing level dropping to 800 m.
Saturday: Mix of sun and cloud, northwest winds decreasing from moderate to light, freezing level staying below 800 m.
Sunday: Mix of sun and cloud, light variable winds, freezing level staying below 800 m.
Monday: Cloudy, up to 5 cm of snow, moderate northwest winds, freezing level 1000 m.
Avalanche Summary
No new avalanche observations have been reported.Â
This MIN post from Monday reports a small (size 1) human-triggered wind slab in the alpine, which was thought to have run on surface hoar. Explosive control work conducted Monday produced small (size 1-1.5) storm slabs running on a crust.
Snowpack Summary
By Saturday afternoon, 10-20 cm of snow is forecast to accumulate as the freezing level drops below 800 m. Strong winds from the south are expected to switch to the northwest and decrease. This will likely create a complex pattern of reactive wind slabs on lee features at upper elevations.
30-60 cm of recent snow may overlie a layer of surface hoar on north-facing aspects near and above tree line. Surface hoar is an exceptionally weak layer not often seen in this region, and it typically takes longer to heal. This persistent weak layer warrants investigation and a conservative terrain use strategy. This weekend offers a prime opportunity on the coast to dig in the snow to assess these conditions (and to share your observations via the MIN!).
The remainder of the snowpack is well settled. Depth varies from around 250 to 300 cm at the peaks of the North Shore mountains (1400 m), tapering rapidly with elevation.Â
Terrain and Travel
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Wind Slabs
10-20 cm of new snow with winds changing in direction (from south to west to northwest) may form a complex pattern of reactive wind slabs on leeward terrain features at upper elevations. These areas of concern overlap with where cornices may also be reaching their breaking point.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar may be found 30-60 cm deep on north-facing aspects near and above treeline. This persistent slab problem is not typical for the South Coast, and there is high uncertainty with regard to how quickly it will heal. Reduce this uncertainty by investigating these deeper layers if you are travelling near steep, open slopes at upper elevations.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 29th, 2020 4:00PM
