The new snow may be hiding pockets of old wind slab on south aspects with fresh soft slabs developing in east facing lee features through the day.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
SATURDAY: flurries, moderate westerly winds, a warming trend with a high of -5C at treeline. SUNDAY: light snow with accumulations of up to 7cm by the end of the day, moderate southerly winds, -5C at treeline. MONDAY: 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 sluffing in extreme terrain, and small soft slabs in the immediate lee of wind loaded features are reactive to skier traffic.
Snowpack Summary
New snow 15cm of new snow on Friday, combined with moderate southwest winds have formed fresh soft slabs in lee features in the alpine and at tree-line. Between 80 and 150cm of snow now sits on an extensive persistent week layer. 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. Snow pit tests suggest that human triggering of this interface is still possible, although unlikely, and that if it does fail the overlying slab is stiff enough to propagate the failure over a large distance. 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.