Regions
South Coast Inland.
Observe for the bond of the recent snow with the underlying surface before committing into avalanche terrain. Also be cautious with the lingering weak layer in our snowpack. Don't be complacent -- these are not typical spring snowpack conditions.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
WEDNESDAY: Mostly cloudy with a few sunny patches, light southeast winds, alpine temperature -5 C, freezing level 1500 m.THURSDAY: Mostly sunny, light southwest winds, alpine temperature -4 C, freezing level 1700 m.FRIDAY: Mostly cloudy, light southwest winds, alpine temperature -4 C, freezing level 1700 m.
Avalanche Summary
On Monday, a large slab avalanche was noted in Duffey Lake Road region in alpine terrain. It was likely triggered by a cornice fall during sunny and warm conditions. The slab likely released on the weak layer described in the Snowpack Summary section. Otherwise, whumphing and cracking were noted at ridgetop, failing 10 to 20 cm deep.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
20 to 40 cm of new snow, with the most near Coquihalla Highway, has been redistributed into lee terrain features from northeast switching to southwest 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 at least 1900 m. 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.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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.