Confidence
Fair - Forecast snowfall amounts are uncertain on Wednesday
Weather Forecast
Synopsis: A low pressure system in the north Pacific continues to feed moisture into BC.Tonight: Cloudy with flurries, freezing level around 900 metres, winds from the south west, light to moderate occasionally gusting to strong.Wednesday: Cloudy with flurries, 10 to 20cm of precipitation expected, freezing level up to 1200 metres, ridge top winds light from the west, gusting to strong.Thursday: Cloudy with sunny periods and possible flurries, trace amounts of precipitation, freezing level around 700 metres, ridge top winds light from the west.Friday: Cloudy with sunny periods and scattered flurries. Freezing level around 1000 metres, ridge top winds light from the west.
Avalanche Summary
The Coquihalla area has just experienced a large natural avalanche cycle and the Duffey lake road saw several large explosive controlled avalanches. A rider triggered (large) size 1 was reported in the Duffey lake area on Sunday. With the forecast incoming storms, the hazard is going to be with us for a while still.
Snowpack Summary
Between 50 and 70 cm of recent storm snowstorm snow at upper elevations is sitting on a a variety of weak layers. Strong westerly winds continue to form wind slabs on lee slopes. The two persistent weak layers that remain a concern are:The March weak layer. A combination of hard wind-scoured slab surfaces in exposed terrain, facets and/or surface hoar in sheltered and north aspects, and sun crust on steep solar aspects and is generally widespread throughout the forecast region.A late January/early February crust/facet/surface hoar combo that is still showing up in snowpack tests with hard shear tests. This layer will be with us for a long time, and a slide triggered on this layer would be very large and destructive. Recent warming temperatures will be good for bonding on this layer, but a sudden increase in load, or a large rainfall event could "wake up" this layer and result in very large avalanches. There are also basal facets at the bottom of the snowpack from cold clear weather in early December, but for the most part these have not been a concern. Recent large avalanches have reportedly scoured some avalanche tracks down to the basal facets and even the ground.
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.