Regions
Kootenay Boundary.
The recent storm snow is settling into a slab that sits above a widespread layer of surface hoar. These slabs are expected to remain reactive to human-triggering and conservative terrain selection is important.
Weather Forecast
A ridge of high pressure is the dominant feature for the next couple days. On Sunday, a mix of sun and cloud is expected with light northwest winds in the alpine. Freezing levels are forecast to reach around 700m in the afternoon. On Monday, a mix of sun and cloud is expected with light to moderate southwest winds in the alpine and freezing levels around 500m. On Tuesday, a weak pacific storm system is forecast to reach the region and models are currently showing 10-20cm out of the storm.
Avalanche Summary
On Friday, a skier triggered a size 1 storm slab on a steep convex roll at 1700m on a north aspect. The slab was reported to be 28cm thick and failing on the early January surface hoar layer. Several loose dry avalanches up to size 1.5 were also reported on all aspects between 1900-2300m. On Thursday, explosive control produced numerous storm slab avalanches up to size 2 around Nelson. There was also a report of a size 2 skier remotely triggered wind slab on a steep north aspect at 2200m. This was triggered from 5m away and failed on the early January surface hoar layer down 38cm.
Snowpack Summary
20-40 cm of new snow has fallen in the last week. Warm temperatures and southerly winds have encouraged the formation of isolated pockets of soft slab at and below treeline. Thicker wind slabs are expected to be lingering in leeward features in the alpine. The new snow is resting on a widespread layer of surface hoar. These weak crystals sit above a melt-freeze crust on solar aspects or facets in shaded areas. Between 40 and 60 cm below the surface, the mid-December interface can be found. This layer consists of surface hoar, facets, and/or a melt-freeze crust. Recent snowpack tests from around Kootenay Pass area suggest that it could still be capable of producing human triggered avalanches. The early December rain crust can be found about 20 cm below that, up to an elevation of 1400m. This layer is thought to be gaining strength. The snowpack below this layer is generally strong and well-settled.
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.