The new snow may be hiding pockets of old wind slab on south aspects with new soft slabs developing on north facing lee features through the day.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
SATURDAY: no significant precipitation is expected, moderate westerly winds, accompanied by a warming trend with a high of -5C at treeline. SUNDAY: light snow with accumulations of up to 5cm by the end of the day, moderate southerly winds, -5C at treeline. MONDAY: isolated flurries, light southerly winds, temperatures are forecast to fall to -10C at treeline through the day.
Avalanche Summary
Avalanche professionals in the field are reporting small slab avalanches in the immediate lee of wind loaded features.
Snowpack Summary
Variable winds have produced localized wind effect in the new snow at ridgeline. About 15 to 40cm of snow sits above a crust that extends up to 1800m. A more extensive persistent week layer is buried between 30 and 80cm down. The form of this layer varies depending on aspect and elevation: it can be found as a crust on south facing slopes in the alpine, or as large grained surface hoar and facets below tree-line. The surface hoar is most widespread in an elevation band between 1400m and 1800m although it may extend higher south of Invermere. Snow pit tests suggest that human triggering of this interface is still possible, although unlikely. Below this the snowpack is thought to be mainly well settled.
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.