New snow may take some time to stabilise. Sunny periods may weaken the slab where it is sitting on a buried crust.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Thursday
Weather Forecast
Overnight and Thursday: Becoming overcast this evening with a chance of some convective flurries. Light Easterly winds overnight and during the day. Freezing levels dropping down to 600 metres overnight and rising up to 1300 metres during the day. Some chance of sunny periods in the afternoon.Friday: Overcast with snow starting in the morning and becoming heavy snow fall in the afternoon. Building Southwest winds becoming strong by the afternoon. Freezing levels rising up to about 1500 metres.Saturday: Snow and Southwest wind continuing. Freezing level rising to about 1700 metres.
Avalanche Summary
No new reports of avalanches. I suspect that there was a natural avalanche cycle in the new snow today. New snow or storm slab avalanches in motion may trigger the deeply buried persistent weak layers.
Snowpack Summary
20-30 cm of new snow overnight has added to the load of recent storm snow. The storm slab is sitting on a mix of melt-freeze crusts on solar aspects and well settled snow, surface facets, and surface hoar on shaded aspects above 1500 metres. The persistent weak layers from early March and early February continue to be a concern. The March weak layer of wind-scoured crusts, melt-freeze crusts, and/or surface hoar is reported to be down 70-80 cm. The February crust/facet/surface hoar layer is now deeply buried down 150-250 cm and may still be triggered by heavy loads like cornice falls or storm slab avalanches in motion. Long fracture propagations resulting in very large avalanches are possible with this layer. Avalanches releasing on these layers may step down to the ground during periods of strong solar radiation or warm spring rain.
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.