Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The frontal system will move across the interior on Thursday bringing moderate snowfall to the Cariboos. A ridge of high pressure builds on Friday and cold, dry conditions are expected for Friday and Saturday.Thursday: Snowfall 15-20 cm, freezing levels may rise as high as 1500m as the warm front crosses the region, moderate SW ridgetop winds gusting up to 60 km/hrFriday: Mostly cloudy and light flurries in the morning, a mix of sun/cloud and drying conditions for the afternoon, treeline temperatures will drop to around -10C in the afternoon, light NW ridgetop windsSaturday: A mix of sun and cloud, treeline temperatures around -10C, light to moderate NW ridgetop winds
Avalanche Summary
Reports of several natural and skier triggered avalanches on Tuesday. Natural avalanches up to size 2 in wind loaded features at treeline on various aspects. Ski cuts and skier accidentals size 1 from small pockets of wind loaded terrain features at treeline. Most of the recent reported activity has been limited to the storm snow and wind loading with depths varying from 20-40cm. However, there has been reports from weekend of very large avalanches releasing deep within the snowpack (1 to 1.5m) in the Cariboos. Also on Tuesday, several very large, deep released avalanches occurred in the Selkirk Mountains. The potential in the Cariboos for very large, deep avalanches remains a major concern, especially with the additional loading on Thursday.
Snowpack Summary
Around 60 cm of new snow has fallen in the last week. Recent mild temperatures has caused substantial settlement of this new snow. This has created a slab around 20-40cm thick which may overlie softer snow creating an upside-down condition in the upper snowpack. Areas of the region have seen moderate to strong winds from the SW-NW resulting in variable wind slabs. Expect to find touchy wind slabs in exposed lee terrain at and above treeline. A buried rain crust exists below 1600 m and a couple buried weak layers (surface hoar or facets) are now down 80-100 cm deep. Snowpack depths vary, but in general 150 cm of snow can be found at treeline, with 100-200 cm in the alpine. In many places we're still dealing with a relatively thin snowpack (thanks to a windy early season) so there's not a whole lot of snow between riders and the sugary snow (facets) near the ground. The basal facet/crust combo has been recently active in parts of the region and continues to give easy to moderate results in snowpack tests. This basal weakness may be difficult to trigger but if triggered, may result in very large, destructive avalanches.
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.
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.