Avalanche Forecast

Issued: Apr 16th, 2018 4:21PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

mconlan, Avalanche Canada

South Coast Inland.

Monday's snowfall accumulation was the highest in the south of the region. Local amounts of around 10 cm are possible on Tuesday. Observe for the bond of the snow with the underlying surface before committing into avalanche terrain.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

TUESDAY: Cloudy with light snowfall, accumulation 2 to 5 cm with possible higher amounts in localized areas, moderate to strong west winds, alpine temperature -6 C, freezing level 1400 m.WEDNESDAY: A mix of sun and clouds, light south winds, alpine temperature -5 C, freezing level 1500 m.THURSDAY: Morning sun and afternoon clouds, light southwest winds, alpine temperature -4 C, freezing level 1600 m.

Avalanche Summary

Large (size 3) persistent slab avalanches were observed in the far north of the region over the weekend. They were about 60 to 80 cm deep, on northwest to east aspects, between 1800 and 2200 m, and failed naturally on the weak surface hoar layer described in the Snowpack Summary section. They propagated widely across the slopes. Otherwise, many slides in the recent storm snow were observed, often triggered by cornice failures.

Snowpack Summary

10 to 30 cm of new snow, with the most in the south of the region, has been redistributed into lee terrain features from northeast winds. This overlies variable surfaces, including wind slabs at high elevations, a sun crust on south aspects, and a temperature crust on all aspects up to 1900 m. Previous wind slabs are up to 1 m deep from strong south winds. On ridges, cornices are reported to be large and fragile.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 50 to 100 cm. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m. Below this, the snowpack is well-settled and strong.The mid and lower snowpack are well-settled and strong.

Problems

Storm Slabs

Monday's 10 to 30 cm of snow may not bond well to varying snow surfaces. Older slabs from the weekend have been most reactive adjacent to ridges in wind-loaded terrain. Watch your overhead exposure, as cornices could trigger slabs on slopes below.

Avoid steep slopes when air temperatures are warm, it is raining, or solar radiation is strong.Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.Use ridges or ribs to avoid pockets of wind-loaded snow.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

Professionals are still travelling cautiously due to a weak layer buried 50 to 100 cm. Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.

Pay attention to overhead hazards like cornices, which could trigger persistent slabs.Avoid steep terrain or areas with a thin or variable snowpack.Be aware of the potential for wide propagation due to the presence of buried weak layers.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Apr 17th, 2018 2:00PM