Regions
Northwest Coastal.
Stormy wet and windy conditions continue. Storm slabs continue to grow in the alpine and natural avalanches are expected.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Wednesday
Weather Forecast
Overnight: The storm continues and freezing levels drop down to 500 metres by morning. This will result in 10-15 cm of new snow combined with strong southwest winds. Wednesday: Another 15-20 cm of new snow above 700 metres with moderate southwest winds. Thursday: A bit cooler with daytime freezing levels around 500 metres, moderate southerly winds and 5-10 cm of new snow. Friday: Strong southwest winds and 10-15 cm of new snow.
Avalanche Summary
Several wet slab avalanches size 2.5 were reported on Tuesday from the Bear Pass area. I suspect that a natural avalanches cycle is ongoing today. Reports may be limited by poor visibility and travel conditions.
Snowpack Summary
Storm slabs continue to develop above 1100 metres. These storm slabs are deep 30-60 cm, with much deeper areas where the wind has transported the snow. Below 1100 metres the snow is moist or wet. The overall results will be widespread touchy storm slabs at higher elevations and unstable wet snow at lower elevations. The storm snow is also stressing a weak interface from February composed of facets, crust, and surface hoar buried over a metre deep. Given the recent activity on this layer before the storm, it should be very reactive during this storm. The lower snowpack is strong, with the exception of basal facets in shallow snowpack areas around Bear Pass and Ningunsaw.
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.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.