Regions
Kootenay Boundary.
Two incoming storms will elevate the danger. Continue to choose conservative terrain and limit your exposure during the storms.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
FRIDAY: Flurries throughout the day with 5-15 cm of new snow and then clearing in the evening, moderate to strong west wind, alpine high temperatures around -6 C.SATURDAY: Another storm pulse brings 20-30 cm of new snow throughout the day, moderate southwest wind, alpine high temperatures around -4 C.SUNDAY: Lingering flurries with light east wind and alpine high temperatures around -15 C.
Avalanche Summary
Wednesday's storm produced a few small (size 1) skier-triggered slabs on north facing terrain at treeline elevations, while explosive control produced a few size 2 avalanches in wind-affected terrain.Last weekend, three large persistent slab avalanches (size 3) were reported on northeast aspects in the Valhallas. Two were triggered with explosive and the third was naturally triggered. These were large avalanches with fracture depths of over a metre. Natural activity on deeply buried weak layers has wound down recently, but human triggering remains a real concern.Expect the incoming snow to form reactive slabs as well as potentially stress deeper weak layers.
Snowpack Summary
Fresh slabs will grow with the incoming storms. A few interfaces buried 20-30 cm below the most recent snow could potentially support wide propagations in the fresh storm/wind slabs. This includes sun crusts on steep south-facing slopes, a rain crust below 1800 m, small surface hoar in isolated areas, and hard wind slabs at upper elevations. Fragile cornices may be found at ridgetop. We now have 1-2 m of settled snow sitting on three significant surface hoar/crust layers that were formed early to mid-January, and back in December. Near the base of the snowpack a crust/facet interface exists that will likely haunt us all season. These persistent weak layers that lurk within the snowpack have produced large and destructive avalanches. Although this activity has been diminishing gradually, recent activity and continued sudden snowpack test results have kept them a top concern in the region.The complex and widespread nature of our multiple overlapping persistent slab problems continues to demand respect and diligence from backcountry travelers in the region.
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.