Regions
Kootenay Boundary.
Another significant storm is expected to roll through and maintain continued high danger for this region.
Weather Forecast
A significant storm is expected to bring around 10 cm new snow tonight and 30-40 cm on Thursday. Freezing levels are expected to peak at around 1700m on Thursday afternoon, meaning that some rain or sleet may fall at lower elevations during the storm. Ridgetop winds are expected to blow up to 70 km/h from the SW. On Friday, unsettled air that moves in behind the frontal system will continue to bring additional snow, but amounts should be lighter, around 10 cm. Winds should ease to moderate southwesterly. Freezing level will lower to around 1000m. On Saturday another storm looks as though it will affect the region, bringing further snow and strong winds.
Avalanche Summary
On Tuesday, several large (size 2.5) fracture lines in commonly skied areas at Kootenay Pass were observed following an intense wind event. On Monday, natural avalanches up to size 2 occurred in response to storm snow loading; ski-cutting to size 1.5 was also reported. This activity continues a very active period of avalanche activity that has been ongoing since early March.
Snowpack Summary
Recent storm slabs of around 20-40 cm overly a variety of surfaces including old wind slabs in exposed areas, a sun crust on southern aspects or even (spotty reports) a 2 - 6mm surface hoar on north and east aspects. Prior to that, recent most snow fell to around 1800m. The leap year SH is now down around 40 - 50 cm and is failing as a resistant planar shear in snowpack tests. The early February surface hoar is down 80 - 140cm, snowpack tests show moderate to hard forces generating sudden planar shears on this layer. Below the early February surface hoar layer, the snowpack is strong in most places.
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.
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.
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.