Regions
Kootenay Boundary.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Thursday
Weather Forecast
A split-flow pattern will be keeping things fairly benign; the most significant change through the forecast period will be warmer temperatures (above seasonal norms), and higher freezing levels. Residual moisture will persist with no significant precipitation. However, more cloud cover will be seen until Friday afternoon.Thursday: Broken cloud cover. Alpine temperatures near 1.0 degree. High diurnal temperature swings up to 2000 m in the afternoon. Ridgetop winds will blow light from the West.Friday: Scattered cloud cover. Alpine temperatures near 3.0. Freezing levels 2000 m and ridgetop winds light from the West.Saturday: Clear skies. Alpine temperatures -2.0 and freezing levels 1900 m. Ridgetop winds light from the West.
Avalanche Summary
On Tuesday, numerous loose wet avalanches and slab avalanches occurred mostly from East-West aspects up to size 2.5. Some of these avalanches ran on the mid-March crust interface.Be aware of continued natural loose wet, or wet slab avalanche activity especially on solar aspects.
Snowpack Summary
Large fragile cornices loom over many slopes. These may become weak and fail due to the influence of the sunshine. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists. Surface snow has become moist up to 2000 m, and melt-freeze crusts are forming on solar aspects. On Northerly aspects surface hoar and surface facetting is occurring.Last week's storm snow has settled into a cohesive slab overlying an old crust (down 50-60 cm) which exists up to ridge top. The crust appears to have gained some strength in most places, but test results are still showing sudden planar fracture characteristics and may be easily triggered in certain areas by riders/skiers, cornices or smaller avalanches. Deeper down, another buried surface hoar layer sits approximately 80 cm. In some places it may not be a concern due to the thick supportive crust that lies above it. However, it may be more reactive to a trigger from a variable, thin snowpack area or a large trigger.
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.