Northwest Coastal

Approaching storm systems are expected to elevate the avalanche danger through Sunday and Monday.

Fair - Intensity of incoming weather systems is uncertain

10-15 cm of snow is expected between 4pm Saturday and 4am Sunday, then a further 5-10 cm during the day on Sunday. Freezing levels on Sunday are expected to be around 1200 m and ridgetop winds around 40 km/h from the southwest. On Monday, another system bringing 10-20 cm new snow is expected with freezing levels around 1300 m and strong southerly winds. On Tuesday, further snowfall (5-10 cm) is expected, with freezing levels around 1000 m.

On Friday, a size 2.5 avalanche was triggered on a north aspect in the alpine. The avalanche appeared to be triggered from relatively low angle terrain and ran in a layer of surface hoar buried around 40 cm below the surface. There were several reports of other deliberately triggered avalanches (ski cuts and explosive triggered avalanches) that could be easily triggered up to size 2. These ran on NW to NE aspects between 1400 and 2100 m. On Thursday, at least four natural avalanches up to size 2.5 were reported from north aspect slopes.

30-50 cm of recent heavy storm snow and, in windy areas, thick wind slabs are poorly bonded to crusts and other slippery previous snow surfaces. In particular, a layer of surface hoar that was buried around 25 March and is now buried around 40 cm below the surface. This layer has been responsible for avalanche activity and whumpfs on northerly aspects in the alpine and at treeline. Some way below this, a hard crust with weak facets, buried early March, may be found over a metre down, particularly in northern parts of the region. Although reports suggest this deeper persistent weakness has gained strength, I'd still be wary of the possibility of isolated large avalanches on steep, unsupported slopes, especially if temperatures increase, or if solar radiation is strong. On sun-exposed slopes and at lower elevations, the snowpack is likely in a spring melt-freeze cycle. The mid-pack is generally well-settled and strong. At the base of the snowpack, weak facets may be found, particularly on shallow alpine slopes in the north of the region.