Regions
Northwest Coastal.
Recently formed storm slabs will continue to be reactive to human-triggering on Thursday and conservative terrain selection remain critical.Use extra caution on south facing slopes in the afternoon if the sun is out in full force.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
5-10cm of snowfall is expected Wednesday overnight throughout most of the region. On Thursday, the south of the region can expect 10-20cm while the north should stay relatively dry with sunny breaks. Freezing levels are expected to be around 800m and alpine winds are forecast to be moderate from the southwest to west. A weak ridge of high pressure is expected to dry out most of the region on Friday except the far south which may see continued light snowfall. Freezing levels are forecast to reach around 1200m and alpine winds are expected to the light from the southeast. The next organized storm system is forecast to arrive Friday night and 10-20cm is currently being forecast for Saturday.
Avalanche Summary
On Tuesday, explosives triggered numerous storm slab avalanches between 1300 and 1500m. These were on all aspects and slabs were typically 15-40cm thick. Explosives also triggered numerous loose wet avalanches between 400 and 700m elevation. Several natural storm slab avalanches up to size 2.5 were also reported in the north of the region. Some of the natural activity was reported to be occurring in steep confined leeward features in the alpine and at treeline. On Monday, several natural wind slab avalanches size 1.5-2 were reported around Terrace. These were mainly on northeast aspects and the average slab thickness was 35cm. A size 1 storm slab was also skier triggered in the Terrace area on a steep convex roll. Storm slabs and wind slabs are expected to remain sensitive to human-triggering on Thursday. If the sun comes out, natural avalanches are possible on steep south facing terrain features. In the far north of the region, deeply buried persistent weak layers may still be reactive to large triggers such as a cornice fall or a smaller avalanche stepping down.
Snowpack Summary
50-100cm of recent storm snow has accumulated over the past week and overlies a melt freeze crust which extends up to around 2000m elevation. This recent snow is reported to be bonding well to the crust. Moist snow was reported below 1200m on Tuesday, wet snow below 800m, and almost no snow below 500m. Recent wind has redistributed the surface snow at higher elevations forming wind slabs in leeward features. The early January surface hoar/facet layer is down 100-200 cm and remains a concern for commercial operations. This layer seems the most reactive in the north of the region and there were several large avalanches reported last week that were releasing on this layer.
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.