Regions
Kootenay Boundary.
New snow and shifting winds will add to existing wind slab problems. Deeper in the snowpack, our lower probability but still high consequence persistent slab problem continues to demand disciplined terrain selection.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Tuesday night: Periods of snow bringing around 8-15 cm of new snow. Light to moderate southwest winds. Wednesday: Mainly cloudy. Light to moderate northwest winds. Alpine high temperatures around -8.Thursday: A mix of sun and cloud with cloud increasing over the day. Light southwest winds. Alpine high temperatures of -10.Friday: Mainly cloudy with flurries bringing 2-5 cm of new snow. Moderate northwest winds. Alpine high temperatures of -9.
Avalanche Summary
Reports from Monday included two skier-triggered wind slabs, size 1 and 2, that released in steeper terrain on north to west aspects at about 2000 metres southeast of Nelson. Several more size 1-2 wind slabs were triggered with explosives in the Valhallas in similar terrain but including southeast aspects. Two persistent slab avalanches were also reported on Monday, both triggered with explosives and ranging from Size 2.5-3. These avalanches released on northeast aspects in alpine terrain and featured crown fracture depths of over a metre.A widespread avalanche cycle occurred last week on all aspects and elevations. Persistent slabs up to size 3 were observed during the peak of the storm loading on Thursday. On Friday and Saturday, natural activity slowed down, but large explosive and machine-triggered avalanches continued to be reported.The natural cycle has wound down, but human-triggering remains a real concern. You might be surprised by how large an avalanche can be triggered and how far it could run.
Snowpack Summary
Up to 10 cm of new snow is expected to accumulate by Wednesday morning. Beneath the new snow, storm snow accumulations from the past week vary from 10-45cm across the region at upper elevations. In the alpine this new snow has been redistributed to leeward slopes from strong northwest winds. Fragile cornices may be found at ridge top. Below 1850 m, around 5 cm of low density snow covers a hard crust. 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.