Avalanche Forecast
Regions: South Coast.
A natural avalanche cycle is expected during periods of rapid loading, as the snow is loading a buried weak layer. Travel in avalanche terrain is not recommended.
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
SATURDAY NIGHT: Increasing cloud and late-night snowfall, accumulation 2 to 5 cm, strong southwest wind, treeline temperature -3 C, freezing level 1000 m.
SUNDAY: Cloudy with snowfall, accumulation 15 to 25 cm, strong to extreme southwest wind, treeline temperature -2 C, freezing level 1000 m.
MONDAY: Mix of sun and cloud, light to moderate northwest wind, treeline temperature -5 C, freezing level 500 m.
TUESDAY: Mix of sun and cloud, light west wind, treeline temperature -3 C, freezing level 800 m.
Avalanche Summary
Although we have not received reports yet, it is expected that natural avalanches released during the storm on Friday night. A natural avalanche cycle is likely to occur during periods of rapid loading on Sunday. The avalanches are likely failing on the surface hoar layer described in the Snowpack Summary.
Snowpack Summary
15 to 20 cm of snow fell Friday night and another 15 to 25 cm of snow is forecast for Sunday, with periods of very rapid snowfall loading. All this snow is loading a weak layer of surface hoar, which was reported to be 10 to 15 mm in size and on all aspects and elevations. The surface hoar overlies a breakable melt-freeze crust, meaning that the surface hoar will likely act as an easy sliding layer for all the storm snow. The snow will also fall with strong to extreme southwesterly wind, meaning slab properties should develop quickly.
The remainder of the snowpack is well-settled.
The snowpack depth varies from around 200 to 250 cm at the peaks of the North Shore mountains (1400 m) and rapidly decreases with elevation to no snow below 1000 m.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy snowfall.
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
Avalanche Problems
Storm Slabs
Storm slabs could reach 30 to 40 cm in thickness by midday Sunday, which overlies a weak layer of surface hoar crystals. Weather models are showing snowfall rates of up to 5 cm an hour Sunday morning. The snow will also fall with strong to extreme southwest wind, which will form slab properties within the snow quickly, particularly at treeline and alpine elevations. This is all a recipe for a natural avalanche cycle to occur on Sunday.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 2.5