Regions
Northwest Coastal.
Snow, wind, and rising freezing levels will increase the avalanche danger. Deeply buried persistent weak layers may be triggered by the increased load from the storm. Patience and a conservative approach to terrain are recommended.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
20-30 cm overnight with extreme southwest winds and freezing level around 800 metres. Another 10-20 cm during the day on Friday with strong southwest winds and freezing levels around 800 metres. Light snow on Saturday with moderate southerly winds and freezing levels about 500 metres. On Sunday, expect increasing southerly winds, rising freezing levels, and moderate precipitation.
Avalanche Summary
No new avalanches reported from the south of the region. On Wednesday in the north of the region there were skier controlled and remotely triggered avalanches up to size 1.5 in the storm snow or on the rain crust from the late January storm. Conditions are expected to change rapidly overnight with storm slabs developing on all aspects and at all elevations.
Snowpack Summary
In the north of the region there is 20-30 cm of new snow that has been transported into deep windslabs above loose facetted snow in sheltered areas, and stiff old wind effected surfaces in exposed terrain. In the south of the region we have reports of 10-20 cm of new snow that is sitting on a new surface hoar layer that was buried on February 3rd. Wind slabs developed in the lee of southeast winds on Wednesday, and more widespread storm slabs developed on Thursday. The January 9th surface hoar/facet layer is down 70-150 cm in most places, and remains a concern on all aspects and elevations, especially with heavy and/or thin-spot triggers. Around the same depth you may also find a surface hoar/facet interface from around New Years. There continues to be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem. A conservative approach to mountain travel is still required.
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.