Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Tonight and Friday: Most of the province is under a high pressure system. Expect moderate winds from the W, freezing levels rising up to 3500 m with clear skies. Alpine temperatures could reach plus ~10 C during the day.Saturday: A weakening frontal system will reach the coast which is not suspected to affect the region. Light SW winds rising to moderate in the afternoon and freezing levels going from 3000 m to 1800 m by the end of the day. Clear sky gradually becoming cloudy. Sunday: Ridge of high pressure rebuilds over the coast leading to a clearing trend with mild temperatures.
Avalanche Summary
No new avalanches reported. Older observations were reported dating from after the last storm one of which is a size 3 avalanche that is suspected to have run on a deep persistent weak layer.
Snowpack Summary
The main concern for tomorrow is the unusual warming and solar radiation shock that the snowpack will take. This will weaken the snowpack and cornices which will most likely increase natural avalanche activity on SE and S aspects, but also in shaded areas because of temperatures rising to plus 10 C in the alpine! As well as surface wet slabs and loose snow avalanches, there is the possibility of it stepping down to deeper persistent weak layers (PWL) .Indeed, the late November facet/crust combo and the basal facets could be triggered by a heavy load such as a cornice drop or an avalanche stepping down. Recent snowpack testing produced sudden planar results and good propagation potential on the facet/crust layer down 90 cm on a NE aspect. The basal facet weakness is also a concern and is mostly found in the alpine in shallow rocky areas. The facet/crust layer is found in the alpine and at treeline elevation band.
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.