Regions
Vancouver Island.
Confidence
Moderate - Extreme variability in wind effect.
Travel/Terrain Advice
Avoid recently loaded slopes and rollovers in the alpine and at treeline. Be aware that smaller hard slab avalanches have the potential to have higher consequences than low density slabs. Watch and listen for signs of instability such as shooting cracks or whumpfing. Cold air and snow temperatures will contribute to slower bonding and settlement and the chance of a lingering avalanche problem.
Past Weather
A strong winter storm on Tuesday delivered snow totals up to 40 cm on eastern Vancouver Island with the western and northern areas seeing less accumulation (10-15 cm). Directly following the band of precipitation, strong NE through W winds stripped windward slopes back down to the old crust and deposited the storm snow into lee terrain and also lower elevations. Wednesday and Thursday brought continued cold temperatures and low freezing levels and little to no precipitation.
Avalanche Summary
On Tuesday numerous small soft storm slabs were reported at treeline on NW through NE aspects on all sufficiently steep slopes in the Mount Washington area. These avalanches were touchy to very touchy to ski cutting and were failing on the old crust that was buried 20-40 cm. One natural slab avalanche was observed at treeline on a SW aspect failing at the crust. On Wednesday a small wind slab was triggered at treeline on a SE slope by a snowmobile. Numerous snowmobiles were observed high marking at treeline on an alpine-like feature on a N-NW aspect with no result.
Snowpack Description
Surface - Highly variable distribution of recent storm snow. Exposed crust in all windward (NE-W) alpine and treeline terrain. Pockets of stiff and soft wind slab in lee and protected areas. Sheltered terrain below treeline has low density dry snow of up to 40 cm on the mid December crust.
Upper - Variable dependent on aspect and elevation. 10-40 cm of new snow overlies the old crust layer and has shown poor signs of bonding.
Mid - Well settled.
Lower - Well settled.
Weather Forecast
An arctic ridge of high pressure bringing clear skies and cold outflow winds will dominate Friday and Saturday. Sunday will see a trough of low pressure break through the ridge and bring precipitation to the coast. Cold temperatures, low freezing levels, and light to moderate winds from the SE will accompany the system.
Fri - 0-3 cm of snow. Winds 30-15 km/h northeast.
Freezing levels of 0-800 m
Sat - Trace amounts of snow on the north and south Island. Winds from the southeast 17-40 km/h.
Freezing levels of 0-290 m
Sun - 5-20 cm of snow with greatest amounts in south and east regions. Winds southeast 15-40 km/h veering to 10-18 km/h northwest.
Freezing levels of 0-600 m
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.