Avalanche Forecast
Issued: Feb 29th, 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
Don't let clear skies create complacency with a complicated snowpack. A tricky pattern of wind-drifted snow and an atypical buried weak layer require careful evaluation and terrain selection on Sunday.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Saturday night: Clear, light northwest winds, freezing level staying below 800 m.
Sunday: Mostly clear, light northwest winds, freezing level 900 m.
Monday: Cloudy, up to 5 cm of snow, increasing northwest winds, freezing level 1000 m.
Tuesday: Cloudy, 10-15 cm of snow, moderate west winds increasing to strong, freezing level rising to 1300 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
20-30 cm of snow has accumulated since Friday. Strong winds from the south switched to the northwest and decreased. The winds redistributed the storm snow into a complex pattern of reactive wind slabs on lee features at upper elevations and rapidly loaded cornices. Periods of sun on Sunday are expected to initiate pinwheeling and rollerballs from strong solar radiation on steep, sunny slopes.Â
40-70 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. Check out the latest forecaster blog that offers a deeper dive into these conditions. 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!).Â
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
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- 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
20-30 cm of recent snow with winds changing in direction (from south to west to northwest) has formed 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 40-70 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: Mar 1st, 2020 4:00PM
