Regions
Northwest Coastal.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Wednesday: Moderate snowfall (up to 10cm) expected near the coast, tapering off rapidly with distance inland, meaning many areas likely to stay dry. Freezing levels around 1000 m. Strong ridgetop winds gusting in excess of 80 km/h from the SW.Thursday: Up to 10cm new snow, again focussed along the coast. Freezing levels remaining around 1000 m. Ridgetop winds 60-80km/h.Friday: Light snowfall, Freezing levels dropping to around 500 m. Winds becoming moderate southerly.
Avalanche Summary
On Monday, avalanches up to size 2 were observed in the recent storm snow at all elevations. Although they appeared to only affect the top 10-20 cm of the snow surface, they were reported to be running far. Sluffing on steep terrain has also been reported.
Snowpack Summary
The recent new snow was warmer and denser in places than the existing snow on the ground, helping to create touchy storm slab conditions. The upper slab, while generally thin, was highly reactive in many places on Monday. Winds marked a significant shift from mostly light northerly to a period of strong south southwesterly to southeasterly. These have set up touchy wind slabs in many exposed lee areas. There are two surface hoar layers in the upper snowpack. The upper one formed at the end of December and is buried approximately 30 cm below the surface. Professionals have reported easy, sudden planar compression test results on this layer and it has been reactive to skier-triggering. The lower one formed at the beginning of December and is buried approximately 90 cm below the surface. Hard, planar compression tests have been reported on this layer. Near the base of the snowpack, a crust/facet layer continues to give hard, sudden results to no results in snowpack tests. This weakness is unlikely to be triggered by a single person, but it remains possible with a very heavy load (e.g. cornice fall) or from a thin-spot trigger point.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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.