Regions
Northwest Coastal.
Forecast sun and high freezing levels may increase the danger from loose wet avalanches and avalanches stepping down to the deeply buried weak layer.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Overnight and Wednesday: Expect strong East to Southeast outflow winds with sunny skies and no precipitation. The freezing level should be down to valley bottoms overnight and then rise quickly to about 2000 metres.Thursday: Continued warm air at Alpine elevations with moderate outflow winds, mostly sunny skies, and no precipitation.Friday: Mix of sun and cloud with a chance of flurries. Winds becoming strong Northerly.
Avalanche Summary
Natural avalanches up to size 3.0 were reported from several areas of the region due to reverse loading from the outflow winds above the early February persistent weak layer. Forecast strong solar radiation and high freezing levels may cause moist or wet avalanches on Southerly aspects.
Snowpack Summary
Strong N-SE outflow winds have resulted in reverse loading and cross loading in exposed terrain at all elevations, and have scoured exposed windward slopes. The prominent mid February persistent weakness (surface hoar, facets, crust and/or wind pressed surfaces) is down 60-100 cm in the north and 120-160 cm in the south. Snowpack tests are now giving moderate to hard "pops or drops" shears on this weakness, and several whumpfs are still being reported. Basal facets and/or depth hoar remain a concern in shallow snowpack areas in the northern part of the region. Cornices are also large and may become weak if northerly winds start to undercut them.
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.
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.