Regions
Northwest Coastal.
Extreme winds are expected that will set up wind slabs in many areas, as well as making backcountry travel difficult.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Monday: 10-15 cm new snow expected. Freezing levels around 1300 m. Extreme winds gusting to 100 km/h from the southwest. Tuesday: 5-10 cm new snow expected. Freezing levels around 1000 m. Ridgetop winds around 40 km/h from the southwest. Wednesday: 2-5 cm new snow expected. Freezing levels around 1000 m. Ridgetop winds mostly light westerly.
Avalanche Summary
Information has not yet come in regarding activity from the current storm. 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.
Snowpack Summary
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 40-60 cm below the surface. This layer has been responsible for recent avalanche activity and whumpfs have been reported on northerly aspects in the alpine and at treeline. Some way below this layer, 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.
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.