Regions
Kootenay Boundary.
Saturday's storm has all of the the ingredients for large avalanches. Travel in avalanche terrain is not recommended.
Weather Forecast
FRIDAY NIGHT: Storm begins with 10-20 cm, strong southwest winds, and freezing level around 1500 m.SATURDAY: Storm continues with another 15-30 cm (and possibly more around Kootenay Pass), strong to extreme southwest winds, freezing level climbing up to 2000 m.SUNDAY: Clearing skies following the storm as alpine temperatures drop to around -8 C, light west winds.MONDAY: Sunny with cloudy periods, alpine temperatures around -5 C, light winds.
Avalanche Summary
Reports continue to come in about a widespread natural avalanche cycle that occurred during last week's rain event. Avalanches were reported on all aspects and elevations, many up to size 3 and over 100 cm deep. A few large cornice failures occurred as well. Several avalanches in the Bonningtons were reported to step down to the late-February interface, and similar step downs likely occurred in other areas as well. Avalanches at lower elevations entrained significant amounts of wet snow. Activity tapered off on Thursday, but the snowpack has not yet had to time to adjust to the heavy loading and warming.On Saturday, heavy precipitation and warming will result in another round of large natural avalanches with the potential to step down to deep weak layers.
Snowpack Summary
A juicy storm will start as snow on Friday night and switch to rain in the morning to form very touchy storm slabs at high elevations and unstable wet snow at lower elevations. Extreme southwest winds will have a dramatic effect on all exposed terrain and likely form touchy cornices. The storm is burying a rain crust that exists up to about 2200 m. Several deeper weak layers were tested during last week's storm including the late-February facet / surface hoar interface (70-120 cm deep), the mid-February crust (90-130 cm deep), and basal facets in shallow snowpack areas. These layers may remain reactive with additional loading and warming.
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.
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.