Wind slabs below and above tree line are now quite touchy, use caution traveling through this elevation band.A Special Public Avalanche Warning is in effect for this region.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
The southern interior will be under the influence of a weak high pressure system for the forecast period. Partly cloudy skies with some sunny periods and freezing levels at valley bottom overnight, then rising to around 1000 metres during the day. The next Pacific frontal system will move into the area late Thursday afternoon with freezing level forecast to rise above 2000 metres.
Avalanche Summary
Reports continue to advise of natural, skier remote, skier controlled and explosive result avalanches up to size 3. Many of these failed on a crust/facet interface 30 to 50 cm from the surface . Moderate to winds, new snow and rising temperatures increase the likelihood of avalanches. Human triggering remains a real possibility through the forecast period.
Snowpack Summary
Conditions are widely variable across the Purcells. Wind slabs and storm slabs have developed at treeline and alpine elevations. In some areas, these overlie a surface hoar or crust/facet interface from early January and may be easily triggered by a skier or sledder. Reports indicate this persistent weak layer is now 40 to 80cm down in some areas and appears to be quite touchy in some parts of the region. A more deeply buried layer of surface hoar from December is now considered dormant. In general, the lower snowpack is well settled and strong.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.