Regions
Northwest Coastal.
A series of new storms are expected to develop new storm slabs at higher elevations. Deeply buried persistent weak layers continue to be a concern for large avalanches.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Strong southeast winds overnight with light precipitation and freezing levels around 800 metres. Moderate southwest winds with 10-15 mm of precipitation on Friday and freezing levels around 800-1000 metres. Light precipitation and moderate southerly winds on Saturday with freezing levels between 700-1000 metres. Moderate to heavy precipitation on Sunday with moderate southwest winds and rising freezing levels. Heavy precipitation is forecast for Monday.
Avalanche Summary
Explosives control on Thursday resulted in a size 2.5 slab avalanche that released on the persistent weak layer in the north of the region in the Ningunsaw area. On Wednesday, several loose wet slides were reported from the Shames backcountry that were visible in the Geronimo bowl. On Tuesday explosives control in the Bear Pass highway corridor produced slab avalanches in the alpine up to size 4.0 with wide fracture propagations. Reports of natural activity during the recent storm of slab avalanches up to size 4.0 releasing in the storm snow or on the deeply buried persistent weak layer from early January.
Snowpack Summary
Observations have been sparse due to poor flying and travel conditions, as well as poor visibility. In the Shames backcountry on Wednesday there was no crust at 1300 metres ( the highest point the observer reached), and we suspect the crust is only above 1500 metres. There was 50 cm of recent storm snow, with the top 25 cm being rain soaked. This moist and wet storm snow was sitting on the old crust from the previous warm storm at the end of January. Compression tests resulted in moderate shears within the storm snow and on the old crust. The January 9th surface hoar/facet layer is down 70-200 cm across the region and remains a concern for commercial operations. There continues to be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem; however, warm temperatures have increased the likelihood of triggering these layers where they still exist. A very conservative approach to mountain travel is still required.
Problems
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.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.