High danger expected for areas where rain/snow, warm temperatures and high winds come together. Some parts of this region may see less precipitation and the danger may be slightly too high for alpine areas.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
A warm, wet storm is expected to bring 10-15 mm snow/rain on Friday night to wetter areas, and a further 10 mm or so on Saturday. Freezing levels are expected to rise to around 2000 m on Saturday. Sunday: most likely a mix with rain likely in the west, and some clearing in the east. Freezing levels expected to remain very high at around 2500 m. On Monday, light rain, with freezing levels remaining high. Strong southwest Winds are expected throughout the period.
Avalanche Summary
Parts of this region that see good amounts of snow/rain with warm temperatures are likely to see an active avalanche cycle. Areas that stay dry may not see natural avalanches, but human-triggered avalanches will still be possible. Avalanches ran in the region during and after the last major storm, typically running on the mid-January surface hoar layer.
Snowpack Summary
Moist new snow and rain forecast for this weekend will fall on a moderately dense upper snowpack. A weak layer that comprises feathery surface hoar crystals lies buried between 25 and 50 cm below the surface. This "mid-January" weak layer has been responsible for most of the recent avalanche activity. While reports do indicate that this layer is starting to gain some strength in this region, becoming more difficult to trigger when ski-cutting small slopes, I'd still bet on this layer being active during the forecast periods of warming and rain through the weekend.The mid-December surface hoar/crust layer is typically down 60-120cm below the surface. The reactivity of this persistent weak layer appears to be quite variable but the potential still exists for large, destructive avalanches in some areas. The layer appears to be the most reactive at and below treeline. The mid-Nov weak layer comprising facets can still be found near the bottom of the snowpack but has generally become inactive.
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.