Regions
Kootenay Boundary.
Mostly clear and cooler on Sunday before a series of storms begins on Monday. Expect avalanche danger to increase by Tuesday or Wednesday.
Confidence
Poor - Due to the number and quality of field observations
Weather Forecast
An upper trough has been moving from Northwest to Southeast across the interior ranges today. This trough is expected to exit into the prairies overnight after leaving about 5-10 mm of precipitation. The precipitation should be snow to the valley bottoms at the beginning of the storm and become rain or freezing rain up to about 1500 metres. A ridge of high pressure will move in behind the trough bringing gradual clearing and cooler air for Sunday. The next system is forecast to move onto the South coast from the Southwest on Monday. This system looks wet for the lower mainland, but so far models do not show it pushing very much moisture into the interior. Areas in the South along the US border, and the Southeast corner near Fernie may get the most out of this system, but so far that is only expected to be 5- 10 mm of rain at lower elevations, or about 5-15 cm of snow at higher elevations. The Southwest flow looks like it will become more intense on Tuesday; warm, wet, and windy is the word so far, stay tuned for more info.
Avalanche Summary
No new avalanches reported from this region.
Snowpack Summary
A thin new storm slab is starting to develop above the hard crust that was buried around November 28th. There has been about 15-20 cm above the hard crust that may have been transported into windslabs at higher elevations. The developing storm slab may not bond well to the old surface where it became facetted during the cold spell last week. Some areas may have had a layer of surface hoar buried yesterday (December 5th) that could provide a weak bond to the new snow. The November 20th crust may be anywhere from about 40 cms above the ground in deeper snowpack areas to on the ground or non-existent in shallower snowpack areas. The November 20th crust continues to give moderate planar results in snow profile tests in some areas; that means the right combination of load and terrain features may result in an avalanche down this buried 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.
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.