Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A substantial storm system is expected to reach the south coast on Saturday morning. Heavy precipitation and strong winds are expected for Saturday and Sunday but conditions should progressively ease during the day on Sunday. A ridge of high pressure should build on Monday resulting in dry, clear conditions.Saturday: Snow 20-30cm, freezing levels am: 1000m pm: 1500m, ridgetop wind 40-60 km/h SW in the afternoonSat. Night/Sunday: Snow 20-30cm, freezing levels am: 1500m pm: 1000m, ridgetop wind 40-60 km/h SW in the morning, easing during the dayMonday: Dry conditions, freezing levels am: 500m pm: 1000m, ridgetop wind light NW
Avalanche Summary
No new slab avalanches have been reported. Loose sluffing has been reported form steep solar aspects during the heat of the day.
Snowpack Summary
The new snow is falling on a weak layer consisting of a well developed sun crust on solar aspects and surface hoar in sheltered areas and on north aspects. At lower elevations, a crust can be expected in most areas. Strong S-SW winds are forecast and can be expected to quickly form new 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. The early-March crust/facet layer is 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.