Regions
South Coast Inland.
Monday's snowfall accumulation was the highest in the south of the region. Local amounts of around 10 cm are possible on Tuesday. Observe for the bond of the snow with the underlying surface before committing into avalanche terrain.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
TUESDAY: Cloudy with light snowfall, accumulation 2 to 5 cm with possible higher amounts in localized areas, moderate to strong west winds, alpine temperature -6 C, freezing level 1400 m.WEDNESDAY: A mix of sun and clouds, light south winds, alpine temperature -5 C, freezing level 1500 m.THURSDAY: Morning sun and afternoon clouds, light southwest winds, alpine temperature -4 C, freezing level 1600 m.
Avalanche Summary
Large (size 3) persistent slab avalanches were observed in the far north of the region over the weekend. They were about 60 to 80 cm deep, on northwest to east aspects, between 1800 and 2200 m, and failed naturally on the weak surface hoar layer described in the Snowpack Summary section. They propagated widely across the slopes. Otherwise, many slides in the recent storm snow were observed, often triggered by cornice failures.
Snowpack Summary
10 to 30 cm of new snow, with the most in the south of the region, has been redistributed into lee terrain features from northeast winds. This overlies variable surfaces, including wind slabs at high elevations, a sun crust on south aspects, and a temperature crust on all aspects up to 1900 m. Previous wind slabs are up to 1 m deep from strong south winds. On ridges, cornices are reported to be large and fragile.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 50 to 100 cm. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m. Below this, the snowpack is well-settled and strong.The mid and lower snowpack are well-settled and strong.
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.