Regions
Vancouver Island.
Confidence
Moderate - Limited info from weather stations but daily info from the field at Mt Washington and Mt Cain.
Travel & Terrain Advice
As temperature begin to drop below zero on Monday we can expect a rain crust to form on all elevations and aspects. New snow in moderate amounts will then deposit on this crust. The bond to this crust and the amount of new snow will be the thing to watch over the next few days. Expect this bond to be poor and slow to gain strength. Avoid areas of deep deposit like wind loaded N-NE aspects in the alpine, treeline and treeline like features below treeline. Large open slopes, wind filled gullies, convex rolls and steep unsupported slopes will be prone to triggering naturally and certainly with human activity. Use ski poles, probes or other devices to test new snow depths as you travel and check the bond to the crust, even with simple hand shears.
Avalanche Summary
Friday: Numerous loose dry sloughs up to 1.5, all aspects on steep slopes in the treeline and below running fast (no alpine obs). Saturday: Sensitive storm slabs observed in the upper snowpack. Many active windslabs on NE-NW asp at treeline size 1-2 around Mt Washington and Cain, triggered with explosives, ski cutting and skier accidentals. One natural triggered size 3 in the closed North bowl zone at Mt Washington. The majority of these were running down to a depth between 20-50 cm on the interface between the huge snow event last Saturday-Sunday and the new storm snow that fell in the days after. No observations for Strathcona Park reported. Sunday: Moderate new snow overnight then moderate to heavy rain produced numerous loose wet up to size 1 and a few wet slab up to size 2 with ski cutting and explosive work on Mt Washington. No other reports for this period but would expect this to be a widespread avalanche cycle for the entire forecast area.
Snowpack Summary
Moderate amounts of new snow have fallen since the huge snow event two weekends ago. Numerous shears/failures have been active in this new snow, with the most interesting between the new and old big snow event down 30-50 cm. Failures have released with moderate to easy results (natural, and human triggered) and are smooth and planar (ie. scary, evidence the size 3 natural in Mt Washington’s North bowl). On Sunday the cold temps and amazing powder skiing we had came to an abrupt end with high freezing levels, warm temps and moderate to heavy rain. The upper snow pack became moist and wet Sunday and travel became difficult. Rapid settlement of the upper snow pack resulted due to the rain and lead to widespread instability.
Snowpack Details
Surface: Rain crust on all aspects and elevations due to Sunday's rain event. Upper: Moist down below the crust. Mid: Numerous weak layers between last weeks new snow interfaces. Test results producing easy-moderate smooth failures. Lower: Well settled including the large snow events accumulation.
Past Weather
Moderate snow fall and very cold temps for the island (-4 to -8) Thursday night though till Sunday morning for the entire forecast region. Sunday mid morning moderate to heavy rain fall all the way to the top of the islands summits as the freezing level and temperatures took a 24 hour spike. Winds were Light to moderate from the SE-SW.
Weather Forecast
Temps will drop and we will see light to moderate new snow accumulation. Winds will be strong to moderate mainly form the S-SW and freezing levels will remain low.Monday: More rain 7-24 mm switching to snow 3-16 cm, positive temps around 2 to 3 will drop by the end of the day down to -2 to -4, with strong to moderate winds from the SW. Freezing levels 2000 m dropping to 1000-800 m.Tuesday: Moderate new snow 10-25 cm, with cold temps -3 to -6, and strong to moderate SW winds. Freezing levels 900 m to 500 m.Wednesday: Light to moderate snowfall 4-20 cm, cold temps -4 to -6, and light to moderate winds from the SW-SE. Freezing levels 300 m to 800 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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.