Recent storm or wind slabs in the alpine may continue to be reactive to human triggers. Avoid slopes below cornices, sun and daytime warming may result in natural releases.
Confidence
- Timing or intensity of solar radiation is uncertain on Tuesday
Weather Forecast
Overnight: Light winds, mostly clear with freezing to valley bottoms. Tuesday: Mix of sun and cloud with moderate southwest winds and daytime freezing up 1500 metres. Wednesday: Overcast with light snow in the afternoon. Moderate southwest winds and daytime freezing up to 1800 metres. Thursday: 5-10 cm of new snow above 1200 metres by morning. Light winds during the day with daytime freezing up to 1600 metres.
Avalanche Summary
No new avalanches reported. Spring melt-freeze cycle ongoing, expect moist snow at lower elevations and on solar aspects in the afternoon.
Snowpack Summary
Last week's stormy weather brought up to 40 cm of snow to upper elevations. This storm snow overlies a rain crust below about 2000 metres and a sun crust on solar aspects at higher elevations. Several other temperature and or solar crusts are likely to exist within the storm snow, mainly at lower elevations and on solar aspects. Moderate to strong southwest winds during and since the snowfall formed wind slabs on leeward slopes and promoted the growth of large, fragile cornices along ridgelines. At higher elevations, the February weak layers are down about 120-150 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. Cornices and wind slabs are also weakened by these warming effects and have the potential to trigger deeply buried weak layers if they release.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.