Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Synopsis: Low pressure systems in the north Pacific continues to feed moisture into BC.Tonight: Cloudy with flurries, no serious precipitation expected, freezing level around 400 metres, winds from the west occasionally gusting to moderate.Tuesday: Cloudy with snow, trace to possible 5cm of precipitation, freezing level climbs to 1200 metres, winds from the south west light, gusting to moderate.Wednesday: Cloudy with flurries, possibility of 10 to 15cm of precipitation, freezing level around 900 metres, ridge top winds moderate from the west.Thursday: Cloudy with sunny periods and isolated flurries, 5 to 10cm of precipitation, freezing level around 1000 metres, winds light occasionally gusting to moderate from the west.
Avalanche Summary
The Coquihalla reported a large natural avalanche cycle yesterday with avalanches up to size 3. A size 2 was rider triggered in the needle peak area with a serious involvement. A rider triggered (large) size 1 was reported in the Duffey lake area from yesterday
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 SW storm winds have formed 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.With recent storm snow loading, the March layer is now down around 60 to 70cm and the early February layer should be roughly 1.8m. These persistent weak layers may still pose a threat for some time in the forecast region.
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.