Confidence
Fair - Timing or intensity of solar radiation is uncertain on Saturday
Weather Forecast
A ridge of high pressure will continue to dominate the region bringing dry conditions and mainly clear skies for the foreseeable future. Winds should be light to moderate from the west on Saturday, becoming light and northwesterly on Sunday and Monday. An inversion is expected for Saturday bringing valley cloud and alpine temperatures reaching +5.0. More seasonal temperatures are expected for Sunday and Monday.
Avalanche Summary
Several large and very large natural and explosive-triggered slab avalanches were observed in the region over the past week. Many of the avalanches started within the recent storm snow, and then stepped down to basal facets at ground level. In at least 2 reported cases, natural cornice fall was the trigger. One report included a size 4 avalanche in the Jumbo area which took out 5 ha of mature trees, up to 100yrs old,Forecast warm temperatures will increase the likelihood of continued deep slab activity.
Snowpack Summary
Last week's snowfall amounts were highly variable throughout the forecast area, with the western parts of the range getting as much as 90cm. Strong to extreme winds pounded the storm accumulations into hard wind slabs in most areas. The recent storm snow sits on a variety of snow surfaces including older wind slab, a soft layer of facetted snow and/or surface hoar buried in early January.In the mid pack you may find a surface hoar layer buried in mid December. Further down you may also find the December facet/crust combo. Both interfaces give variable results in snowpack tests, but professional operators are treating them with caution.The biggest concern throughout the region is a layer of weak sugary depth hoar at the base of the snowpack. These crystals may coexist with a crust which formed in October. Several large avalanches in the past few weeks have been attributed to failures at this layer. Wide propagations on relatively gentle terrain have been noted, and an alarming tendency for seemingly disconnected slopes to propagate over a wide area and produce large avalanches. Forecast warm temperatures will increase the likelihood of continued avalanche activity at this interface
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.
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.