Regions
Kootenay Boundary.
Cautious terrain selection is critical these days. Pay attention to daytime heating on solar aspects and avoid cornice features.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
A ridge of high pressure has moved in over province. We should see mostly sunny skies with a few clouds and the possibility of morning valley fog in some areas. Freezing levels are forecast to rise to 1500 metres during the day, but should drop to valley bottoms overnight. On Friday, freezing level may go to 3000 metres.
Avalanche Summary
Reports from yesterday tell us that wind slab avalanche activity is still not over. A widespread cycle of natural activity in the Bonnington range up to size 2.5 was also reported, and seems to have been the storm snow from the last wind and snow event. The February crust interface mentioned in the Snowpack Discussion section appears to be still active in some parts of the region, and is still something to be wary of. Warm temperatures and increased radiation on solar aspects makes for a good recipe for large avalanches.
Snowpack Summary
A considerable amount of snow fell during the past week, with the eastern part of the region receiving the most out of the storms. Moderate to strong south west winds have redistributed the surface snow into touchy wind slabs. A melt-freeze crust that formed during the 2nd week of February has been reported at various levels from 50 to 120cm throughout the region. This crust is widespread and may co-exist with surface hoar or weak facets, especially at treeline and below on north aspects. This reactive interface is a critical layer to watch in the region, and has been the active layer for some very large avalanches recently. Buried surface hoar layers exist in the drier areas on the west side of the region near Rossland and are worth keeping in mind. Surface hoar growing up to 6mm has been reported in the past 2 days throughout the region. Sun crust may exist on solar aspects at the surface and has also been reported in the region 20cm below the surface. Daytime heating will help settle the snowpack but could also make for touchy conditions on south facing slopes in the afternoon. Cornices can grow weak with daytime heating.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.