Storm slabs and pockets of wind loaded snow may continue to be reactive to human triggers. Cornices may become weak and release naturally during the heat of the day; avoid slopes below cornices.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Tuesday
Weather Forecast
Overnight: High overcast with light winds and freezing down to valley bottoms. Tuesday: Mix of sun and cloud with moderate southwest winds and daytime freezing up to 1400 metres. Wednesday: Overcast with afternoon flurries and moderate southwest winds. Daytime freezing up 1800 metres. Thursday: A few cm of new snow by morning. Winds becoming light and daytime freezing around 1800 metres.
Avalanche Summary
Natural storm slab avalanches up to size 3.0 were reported on Sunday from both the Monashees and the Selkirks. Natural and explosives controlled cornice falls released up to size 2.5 on their own, and up to size 3.0 where they pulled a slab on the slope below. A solid overnight re-freeze down to valley bottoms is forecast, setting up a spring melt-freeze cycle over the next few days.
Snowpack Summary
10-20 cm of recent snow now overlies a crust below about 2200 metres on (higher on solar aspects) and moist snow below about 1700 metres. Below the new snow interface, storms over the past week brought 40-60 of snow to the region. Several other crusts as well as moist snow are likely to exist within this storm snow, mainly at lower elevations and on solar aspects. Moderate to strong southwest winds during and since the storm formed wind slabs on leeward slopes as well as fragile cornices along ridgelines. 90-130 cm of accumulated snow now overlies a more widespread rain crust below 2000 m and sun crust on solar aspects at higher elevations. At higher elevations, the February weak layers are down 160-200 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases were also reported in late March and these deeply buried weaknesses remain a serious concern as solar radiation and warming temperatures begin to penetrate the snowpack at increasingly higher elevations.
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.