Regions
Northwest Coastal.
Stormy weather will elevate the danger this weekend. Minimize your exposure to avalanche terrain when there's rapid loading from new snow and wind.
Confidence
Moderate - Timing of incoming weather systems is uncertain
Weather Forecast
SATURDAY: 10-20 cm Friday night then clearing and cooling throughout the day, strong northwest wind, freezing level dropping back to valley bottom.SUNDAY: The next system arrives Sunday morning delivering 10 cm snow throughout the day and continuing into the evening with another 15-30 cm Sunday night, moderate west wind, alpine high temperatures around -8 C.MONDAY: Clearing throughout the day with isolated flurries, light to moderate southwest wind, alpine high temperatures around -5 C.
Avalanche Summary
Natural avalanche activity was observed on Friday morning, producing several 30 cm thick slabs in the latest snow.A few persistent slab avalanches released on Wednesday, most likely failing on the mid-January crust. This includes a natural size 3 avalanche on a southwest slope at 1150 m near Exstew, a few skier triggered slabs (size 1-2) in thinner snowpack areas (east of Terrace and the northern part of the region). The mid-January layer was also active in the Shames area last Saturday, where a skier triggered a size 2 avalanche on a northeast alpine slope. In this case, the weak layer was composed of surface hoar. Overall, activity on persistent weak layers has been limited recently, but enough to suggest these layers may remain reactive through this current storm.
Snowpack Summary
Fresh snow will continue to accumulate the next few days. In some areas up to a metre of storm snow has already accumulated over the past week. Warm temperatures are promoting the settlement of new snow, while westerly winds are blowing snow around in exposed areas.A weak layer buried in mid-January remains a concern and is now 60-100 cm deep. 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.