Regions
Northwest Coastal.
Storm slabs are expected to remain sensitive to human triggering and a window of sun Monday afternoon could initiate a round of natural avalanche activity. Take a cautious approach and minimize your exposure to overhead avalanche terrain.
Confidence
Low - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A strengthening ridge axis on Monday offers a brief lull in the action before the next system slams into the Northwest Coast on Tuesday, bringing significant snow and wind that is expected to last through Wednesday night. MONDAY: Overcast with some clearing in the afternoon, freezing level at valley bottom, light to moderate northwest wind, trace of snow possible. TUESDAY: Overcast, freezing level at valley bottom, moderate to strong west/southwest wind, 15 to 25 cm of snow. WEDNESDAY: Overcast, freezing level around 750 m, moderate to strong southwest wind, 15 to 30 cm of snow.
Avalanche Summary
On Saturday wind and storm slab avalanches failed naturally to size 2 on a variety of aspects in both alpine and treeline elevation bands. A natural size 3 persistent slab avalanche was observed on a steep north facing alpine feature with a crown up to 100 cm in depth, which suggests the mid-January interface was involved. A another very large avalanche (size 3.5) was reported from an unknown aspect/elevation. Natural avalanche activity was observed on Friday morning, producing several 30 cm thick slabs in the latest snow. A large (size 3) storm slab avalanche was reported on a east aspect east of Terrace.A few persistent slab avalanches released on Wednesday, most likely failing on the mid-January crust. This included a natural size 3 avalanche on a southwest slope at 1150 m near Exstew and a few skier triggered slabs (size 1-2) in thinner snowpack areas (east of Terrace and the northern part of the region). Overall, activity on persistent weak layers has been limited, but large persistent slab avalanches may remain possible during periods of heavy loading or rapid warming.
Snowpack Summary
The weekend storm produced up to 35 cm of new snow, the region has now received up to a metre of snow over the past week, but warm temperatures have promoted settlement and reduced this amount to 50-70 cm. Westerly winds are forming fresh wind slabs in exposed terrain.A weak layer buried in mid-January is 60-100 cm below the surface and remains a concern. In most areas this layer is a crust, but it may also be surface hoar in sheltered areas at treeline and below. This layer produced a few human triggered avalanches throughout the region over the past week, and may remain reactive as it adjusts to the weight of the new snow.In thinner snowpack areas (north and inland), deeper crust / surface hoar layers that were buried in December and early January may still be a concern. They are buried over 100 cm below the surface, but may be triggerable from thin spots.
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.