Regions
Kootenay Boundary.
Touchy storm slabs becoming more likely to trigger. Conservative decision making will be Critical to playing safe in the mountains on Monday.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Sunday night: 10-15 cm new snow / Moderate, southwesterly winds / Freezing level 900 m.Monday: 15-25 cm new snow / Moderate, southwesterly winds / Freezing level valley bottom.Tuesday: Mostly cloudy / Light to moderate, southwesterly winds / Freezing level valley bottom.Wednesday: Mostly cloudy with flurries / Light to moderate, southeasterly winds/ Freezing level valley bottom.
Avalanche Summary
On Saturday, numerous natural avalanches to size 1.5 and explosive triggered storm slab avalanches to size 3 were reported near Kootenay Pass. The fresh storm slabs were reported as being very reactive to human triggers throughout the region. Avalanche activity is expected to increase on Monday with the additional snow and wind.
Snowpack Summary
25-45 cm of recent storm snow has created touchy storm slabs at all elevations and aspects. Another 25-45 cm is expected by Monday evening bringing storm totals to 50-90 cm. Snowfall amounts are expected to be highest around Kootenay Pass and taper dramatically as you go north. These slabs have been reported as being very reactive to human triggers and are sitting on a variety of surfaces; including scoured surfaces in wind exposed terrain, surface hoar(size 2-3 mm) in sheltered locations, and sun crust on steep solar aspects. 40-70 cm of snow now overlies the weak layer of surface hoar(feathery crystals) and facets(sugar snow) that was buried in mid-January. There have been no recent reports of avalanches on this interface, but this may change with the increasing load. Areas with a shallower snowpack (less than 150 cm) have a generally weak snowpack structure with sugary facets near the ground. This includes shallow alpine slopes and most of the Rossland range. It is possible for storm slab avalanches to step-down to these deeper weak layers, resulting in large, destructive avalanches.
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.