Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The storm is expected to end on Sunday evening. A ridge of high pressure will build in the wake of the storm system. Dry, sunny conditions are expected for Monday into Tuesday. The next frontal system should reach the south coast on Tuesday night.Sat. Night/Sunday: Snowfall 25-35cm, freezing level am: 1500m pm: 1000m, ridgetop winds 30-50 km/h SW easing during the day.Monday: Mostly sunny, dry conditions, freezing level am: 500m pm: 1000m, ridgetop winds light NWTuesday: A mix of sun and cloud, dry conditions with the possibility of snow in the evening, freezing level am: 500m pm: 1200m, ridgetop winds light W-NW
Avalanche Summary
Limited reports from Saturday suggest avalanche activity was limited to wind loaded features. More widespread storm slab activity is expected for Saturday night and Sunday as the storm progresses.
Snowpack Summary
The storm snow is sitting on a weak layer consisting of a well developed sun crust on solar aspects and surface hoar on shady, sheltered slopes. At lower elevations, a crust can be expected in most areas. S-SW winds are forming wind slabs on leeward slopes. Below the storm snow, the upper snowpack is generally well settled from the recently warm weather. There are two persistent weak layers which remain a concern but the problem is becoming isolated. Before the storm, the early-March crust/facet layer was down roughly 1m and the early-Feb layer is down 1.5m or more. These layers are typically deep enough that human-triggering is unlikely but smaller avalanches or cornices have the potential to step down to these layers. Freezing levels have been cycling between valley bottom and 1500-2000m, and low elevation terrain saw significant rain last weekend. The snowpack at lower elevations has been generally stable but wet snow or rain may destabilize the upper snowpack.
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.
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.