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.
Confidence
High - The weather pattern is stable
Weather Forecast
A well-embedded ridge of high pressure will keep the region warm and sunny for Thursday and Friday, while increased cloud is forecast for Saturday. Freezing levels should hover around 2800m for each day of the forecast period. Ridgetop winds will remain generally light.
Avalanche Summary
A few small wet slabs were observed around Kootenay Pass on Tuesday. They undoubtedly occurred in response to warming and solar radiation. At the time of publishing no other avalanches were reported, although this may reflect a lack of observations rather than actual conditions. The sun has become the main driver for avalanche activity. Although warming has promoted settlement and strengthening within storm snow from last weekend, loose wet avalanches and cornice falls have become the most common avalanche type. A major concern, however, remains isolated yet destructive releases on deeper weak layers which formed earlier in the season (see snowpack description). 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
On shaded slopes above 1900m you'll still find cold winter snow which is reported to be settled and faceted on sheltered slopes, and wind-affected in exposed areas. Warm temperatures have promoted a daily melt-freeze cycle on all other snow surfaces. Cornices are large and looming and have become increasingly weak with the sunny weather. In the upper snowpack you'll likely find a few hard crusts which exist everywhere except on high, north-facing terrain. The late February surface hoar/ crust interface (down 80 to 130 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.
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.
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.