Regions
Vancouver Island.
Confidence
Moderate - Limited field observations from storm on Tuesday.
Travel/Terrain Advice
Avoid steep convex rolls and be aware of recent reverse wind loading especially at ridge top. Take note of the depth of new snow over the old crust surface and if that snow is sticking to it. Recognize the potential for wide slab propagation and utilize safe zones and minimize exposure of suspect slopes to one at a time.
Past Weather
A series of low pressure systems peaking in intensity on Tuesday have brought moderate snowfall to the Island mountains. Sunday saw elevated freezing levels and rain to about 1400 m followed by dropping freezing levels and temperatures. The bulk of new snow has come Tuesday in a NW to NE flow which is not the common pattern.
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 also failing at the crust.
Snowpack Description
Surface - 30-40 cm of low density snow with variable distribution due to moderate to strong NW through NE winds overlies the old crust. Some windward slopes have been stripped down to the crust. Expect wind loaded pockets on lee slopes up to 50-60 cm deep.
Upper - 40-60 cm of new snow load is now on the old crust surface and is bonding poorly. Some sugary snow has been observed below the crust especially on northern aspects in the alpine.
Mid - Well settled.
Lower - Well settled.
Weather Forecast
Another high pressure system begins to build off the Pacific coast and will bring clearing skies, cooling temperatures and dropping freezing levels. This ridge should prove to be a clean ridge, meaning no low level clouds and fog, just cold and clear. Minimal precipitation in the foreseeable future.
Wed - No new precipitation. Winds 30-40 km/h north veering to 20-15 northwest.
Freezing levels of 0-850 m
Thu - Trace amounts of snow on the north and east Island. Winds from the west 10-20 km/h.
Freezing levels of 0-950 m
Fri - No new precipitation. Winds northeast 15-40 km/h.
Freezing levels of 0-850 m
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.