Regions
Kootenay Boundary.
Solar warming will drive the Avalanche Danger throughout the forecast period. Watch your overhead hazard as large and destructive avalanches may reach their run-out zones.
Weather Forecast
A well-embedded ridge of high pressure will keep the region warm and sunny for the forecast period. Ridgetop winds will be generally light, while freezing levels will sit at about 2200m on Wednesday and then climb to about 2700m for Thursday and Friday.
Avalanche Summary
On Monday, storm slabs (mostly in the size 1.5 range) were reported in high elevation, wind exposed terrain. The sun will become the main driver for avalanche activity throughout the forecast period. Although warming will promote settlement and strengthening within the recent storm snow, loose wet avalanches and cornice falls will become the most common avalanche type. My main concern, however, remains isolated yet destructive releases on deeper weak layers which formed earlier in the season. Avalanches on these layers could run surprisingly long distances, and may be triggered by a cornice fall, a surface avalanche in motion or extended periods of warming.
Snowpack Summary
13-25cm of new snow from Sunday night overlies small surface hoar on shaded slopes at treeline and in the alpine. Snow surfaces are now well into a daily melt-freeze cycle on all aspects below treeline and sun-exposed slopes at higher elevations. Cornices are large and looming and will become increasingly weak with forecast warming and solar radiation. About 25-50cm below the surface, you'll likely find another hard crust which exists everywhere except high, north-facing terrain. The late February persistent weak layer down 70 to 120 cm remains a low probability / high consequence concern. Test results are variable, with occasional sudden planar (pop) results. While generally becoming unlikely to trigger, this layer could produce surprisingly large and destructive avalanches with a cornice fall or warm temperatures.
Problems
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.