Regions
Kootenay Boundary.
Choose your route to avoid exposure to sun-baked terrain and slopes overhung by cornices.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
Sunday is expected to remain warm, with the freezing level around 2400 m. Clouds and isolated convective showers are possible. A front passing through on Monday is expected to bring around 10-20 mm precipitation and moderate SW winds, with the freezing level falling from around 2500 m to 1500 m. Cloud and a few snow showers may linger on Tuesday.
Avalanche Summary
A natural cycle of size 1-2 loose wet avalanches appeared to slow down on Friday, but an explosives control mission near Nelson produced several size 2-3 wet slab avalanches.
Snowpack Summary
Large cornices overhang alpine slopes and threaten to trigger avalanches on slopes below. These are likely to be fragile due to the warm weather. The snow surface is moist up to at least 2000 m on all aspects and may still be dry on shady aspects at higher elevations. At low elevations, the snowpack is isothermal. 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
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.
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.