Avalanche Forecast

Issued: Mar 27th, 2018 5:01PM

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

Avalanche Canada cgarritty, Avalanche Canada

Strong winds have been forming new wind slabs up high while the bond beneath our new snow remains weak. Err on the side of caution while danger is still elevated.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Wednesday: Mainly cloudy. Strong to extreme west winds. Freezing level to 1000 metres with alpine high temperatures around -8.Thursday: Increasingly cloudy with flurries bringing 3-5 cm of new snow by end of day, increasing overnight. Light southeast winds. Freezing level near valley bottom with alpine high temperatures around -9.Friday: Cloudy with continuing flurries and another 3-5 cm of new snow. Light variable winds. Freezing level to around 800 metres with alpine high temperatures around -8.

Avalanche Summary

Reports from Sunday again included numerous observations of ski cutting producing size 1.5 storm slab releases on small rolls. These slabs were failing at an upper storm interface before stepping down to the full depth of our recent storm snow (about 40 cm). Conservative terrain selection is likely to have limited the size of these results.On Saturday, ski cutting on convex rolls below treeline produced size 1.5 slabs in the recent storm snow down 30 cm deep. These failed over the widespread melt-freeze crust and gathered substantial mass as they traveled downslope.

Snowpack Summary

Up to 40 cm of storm snow now overlies a range of old snow surfaces, including two layers of surface hoar existing on shaded aspects at high elevations as well as a melt-freeze crust on all aspects at treeline and below. This storm snow has been showing a poor bond to the shallowest of these buried weak layers, down about 40cm. Recent strong winds have redistributed the new snow into thicker and likely more reactive wind slabs on a range of aspects wind-exposed terrain. Southwest winds have been the most recent.Deeper in the mid-pack, layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist from mid- and late-February and a surface hoar/ crust layer from January is buried around 150 to 200 cm. Near the bottom of the snowpack, sugary facets exist in colder and dryer parts of the region, such as the far north.

Problems

Storm Slabs

An icon showing Storm Slabs
30-40 cm of recent snow has been settling into a reactive slab over a crust in most areas as well as surface hoar on high shaded aspects. Thicker and more reactive slabs are likely to be found on north to east aspects in wind-exposed terrain.
Watch for signs of instability like shooting cracks or recent avalanches.Be increasingly cautious and watch for patterns of wind loading if you enter wind-affected terrain.Keep your guard up at lower elevations. Storms slabs have been reactive at all elevations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Valid until: Mar 28th, 2018 2:00PM

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