Regions
Kootenay Boundary.
Another storm is on the way and maintaining dangerous avalanche conditions. With two buried surface hoar layers in play, the trees are not the safe haven they normally are. It's time to stick to simple, well-supported terrain.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
THURSDAY NIGHT: 5-15 cm of snow, moderate to strong southeast wind, alpine temperatures drop to -10 C.FRIDAY: Cloudy with scattered flurries and localized accumulations of 5 cm during the day, moderate southwest wind, alpine high temperatures around -6 C, snow picks up in intensity Friday evening bringing another 5-15 cm.SATURDAY: Scattered flurries easing off throughout the day with localized accumulations of 5-10 cm, light wind, alpine high temperatures around -8 C.SUNDAY: Mostly cloudy with clear breaks later in the day, light wind, alpine high temperatures around -12 C.
Avalanche Summary
On Thursday, fresh wind slabs were very reactive to human triggering on all aspects. Two large (size 2) skier-triggered slab avalanches were reported at treeline elevations with crowns up to 80 cm thick. Numerous smaller (size 1) skier-triggered wind slabs were also reported, including some triggered from a distance (remotely).On Wednesday, numerous size 1-2 storm slabs were reactive to human and explosive triggers.On Tuesday, natural and human triggered storm slab avalanches were widespread to size 2 on all aspects/elevations. The storm slabs were very touchy, and some were remote triggered from as far as 50 m away.
Snowpack Summary
Storm slabs will continue to grow thicker and touchier with the incoming storm. 25 to 40 cm of snow from earlier this week has been blown around by strong wind and formed very touchy wind slabs. This snow sits on a variety of old surfaces that include a sun crust on southerly aspects, variable wind affected snow, and weak feathery surface hoar crystals at and below treeline. The snowpack now hosts two buried surface hoar layers. The February 1st surface hoar is down 40 to 60 cm and has been recently reactive to human triggers. The mid-January surface hoar is 60 to 100 cm below the surface. This deeper layer of surface hoar is most prevalent below treeline on shady aspects, but it does not seem to be a widespread problem in the region. Below that, the snowpack is well settled.
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.