Avalanche Forecast

Moderate -

Monday: A mix of sun and cloud. Light southwest winds. Freezing level to 1500 metres with alpine temperatures of -6.Tuesday: Cloudy with sunny periods. Light southeast winds. Freezing level to 1900 metres with alpine temperatures of -3Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate to strong south winds. Freezing level to 2000 metres with alpine temperatures around 0.

Reports from Saturday included an observation of several recent (24 hours old) slab avalanche releases to Size 2.5 from various aspects south of Valemount. Reports from Friday included observations of numerous loose snow releases to Size 1.5 occurring with solar warming near Blue River. Improved visibility also allowed for observations of recent (up to 72 hours old) slab avalanche activity reaching up to Size 4 in the same area. The largest of these avalanches are certain to have failed on deeply buried persistent weak layers.Reports from Thursday included observations of two large (Size 2.5 and Size 3) storm slabs releasing naturally from steep alpine terrain north of Blue River. Crown fractures of these slides ranged from 60-80 cm. Extensive natural sluffing to Size 2 was also observed, with loose dry activity on northerly aspects and loose wet from solar aspects. One Size 1 cornice fall was also reported.Looking forward, anticipate a stark change in the snowpack from morning to afternoon as solar warming breaks down surface crusts and promotes instability in a wide range of avalanche problems over the course of each day.

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.