Regions
Kootenay Boundary.
We're still in a period of dangerous avalanche conditions. A brief break in the weather on Friday won't be enough for the snowpack to stabilize.
Weather Forecast
FRIDAY: Increasing clouds before the next storm arrives Friday evening, light southwest winds increasing throughout the day, freezing level up to 1500 m with alpine temperatures around -3 C.SATURDAY: Storm starts on Friday night and delivers 25-40 cm, strong southwest winds, freezing level up to 2000 m.SUNDAY: Clearing skies following the storm as alpine temperatures drop to around -8 C, light to moderate west winds.
Avalanche Summary
Reports from Wednesday confirmed an ongoing natural cycle of wet slab and loose wet avalanches up to size 3. Much of the activity was between 2000 and 2400 m on a variety of aspects. One large avalanche was triggered by a cornice fall on a north aspect. Explosive control also produced numerous size 2-3 wet avalanches.On Friday, storm slabs will remain reactive at higher elevations, particularly if the sun comes out in the morning. Large persistent slab avalanches also remain a serious concern until the snowpack has time to recover from the recent rain and warming.
Snowpack Summary
After several days of heavy rain, dropping freezing levels have left a thick rain crust up to about 2200 m. At higher elevations, large amounts of storm snow likely exist. At lower elevations, the rain has soaked the upper snowpack up to 50 cm deep. Several deeper weak layers were tested during the 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 a bit longer as the snowpack gradually cools off.
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.