Regions
Kootenay Boundary.
See forecaster blog for a discussion on changing avalanche conditions.
Confidence
Fair - Intensity of incoming weather is uncertain on Saturday
Weather Forecast
By the end of Saturday, high snowfall areas in the region could see as much as 20 cm of low density new snow as a frontal system tracks along the US/Canadian border. Moderate southwest winds are expected and alpine temperatures should hover between -5 and -10C. For Sunday and Monday, a series of weak disturbances embedded in a northwesterly flow will bring light precipitation. Winds should be generally light or moderate, with the switch from southwesterly to northwesterly expected to occur on Sunday night.
Avalanche Summary
Wind slab pockets could be triggered on convex rolls on Friday at higher elevations. Two size 2 human-triggered avalanches were been reported from Kootenay Pass on Wednesday/Thursday, initiating on a surface hoar layer down around 15 cm on north east facing slopes below treeline. Things are changing. Check out the forecaster blog for a discussion on scenarios that may play out as the current situation evolves.
Snowpack Summary
Another 5-10cm of snow on Thursday has brought the total to about 15-25 cm of dry snow above the major surface hoar created at the beginning of the month. Some thin windslab may have developed in the alpine due to moderate westerly winds. This interface will be one to watch as it receives more snow load and/or the slab settles. Below that 30cm of near-surface facets can be found on shady slopes while a sun crust can be found on southerly aspects. In shallow snowpack areas concerns remain for the mid-December persistent weakness down around 80-100cm and for basal facets.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.