Warm temperatures and sunny skies forecast for the next few days will have a significant weakening effect on the snowpack. If solar radiation is particularly strong, the avalanche danger could rise to HIGH.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Tonight and Thursday: The South Coast will remain under a ridge of high pressure bringing dry and warm conditions. Freezing levels are expected to reach 3200 m by tomorrow afternoon, moderate NW winds and mainly clear skies. Friday: The whole Coast is under the high pressure system, clear skies, moderate W winds and freezing levels reaching record levels of 3300 m. Saturday: A frontal system is expected to reach the coast, expect cloudier skies, mild temperatures and winds tapering down.
Avalanche Summary
A skier triggered avalanche size 1 was reported on an E aspect.
Snowpack Summary
The main concern for the coming days is the unusual warming and solar radiation shock that the snowpack will take. This will weaken the snowpack and most likely increase natural avalanche activity on SE and S aspects, but also in shaded areas because of temperatures rising to plus 5 C in the alpine! As well as surface wet slabs and loose snow avalanches, there is the possibility of it stepping down to a deeper persistent weak layer (PWL) especially in the Northern part of the region. These PWLs are most problematic especially in shallower snowpack areas at treeline. Multiple avalanches just ran on the weak basal facet layer recently and whumphing (sudden settlement) were reported yesterday. An early January surface hoar is also buried under ~50 cm of the storm slab in sheltered areas at treeline and below treeline. In the southern part of the region, where the early season snowpack was deeper, these persistent weak layers do not seem to be as prevalent. However, temperatures and solar radiation will be even stronger in this part of the region, making wet slabs and loose avalanches even more probable.
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.