Regions
Kootenay Boundary.
Extra Caution required in alpine and open treeline features.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
5-10cm of snow with moderate southwesterly winds on Friday night. No snow forecasted for rest of forecast period. Freezing levels rise sharply on Monday to 3000+m.
Avalanche Summary
Several skier triggered storm slab avalanches to size 2 were reported on Thursday. These were primarily triggered in lee features at treeline. One natural storm slab size 1.5 was observed on an east aspect at 2000m.
Snowpack Summary
5cm of new snow brings the storm slab to 35-45 cm and can be found across most of the region. This new snow lies above a variable old surface buried at the end of January. This interface is being reported as a layer of surface hoar at treeline in the Rossland area. However, in most other parts of the region the new snow sits on a rain crust and/or old wind slabs. A weak layer buried mid-January can be found down 45-50cm, however, snow pit tests indicate that this layer is gaining strength. Deeper in the snowpack, the persistent weak layer that was buried earlier in January is now down 80-120 cm and continues to give sudden planar fractures in snowpack tests under moderate to heavy loads.
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.