Regions
Northwest Coastal.
Outflow winds may develop new wind slabs at all elevations. New wind slabs may be sitting on a weak layer of surface hoar or sun crust that can act as an easy sliding layer.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
Outflow winds on Wednesday are expected to continue overnight and on Thursday. Some chance of a weak above freezing level developing on Thusday at about 1500 metres elevation. The valleys should stay below freezing as outflow winds carry cold air out towards the coast. On the coast expect freezing levels to rise up to about 700 metres. Light flurries are possible close to the coast, and broken skies are more likely as you move inland. Southwest winds developing on Saturday in advance of a possible storm starting on Sunday.
Avalanche Summary
Some natural wind slab activity size 2.0 was reported from the north of the region near the coast where the outflow winds were reported to be strong. There have been no reports of avalanches from the ski operations in the south or from MIN reports.
Snowpack Summary
Snowpack surfaces are highly variable. Temperature inversions and solar radiation have recently come into play and a melt-freeze crust can be found on steep, solar aspects in the alpine. On most other slopes, 25-40 cm of snow from the Boxing Day storm continues to settle and facet, and new surface hoar has been reported although its distribution is likely variable due to strong outflow winds. In areas where recent winds have been light, shaded slopes will likely provide settled powder. In areas where winds have been stronger, reactive wind slabs may exist, especially in areas where the the slab overlies surface hoar buried by the Boxing Day storm. Professionals in the region are still keeping an eye on a few other surface hoar layers that developed throughout December which are now buried in the top 100cm. Although these layers may be gaining strength, they are worth keeping an eye on, especially on steep unsupported slopes at treeline and below. In colder and shallower snowpack areas watch for weak basal facets.
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.