Avalanche Forecast

Issued: Apr 17th, 2018 3:45PM

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

mconlan, Avalanche Canada

South Coast Inland.

Observe for the bond of the recent snow with the underlying surface before committing into avalanche terrain. Also be cautious with the lingering weak layer in our snowpack. Don't be complacent -- these are not typical spring snowpack conditions.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

WEDNESDAY: Mostly cloudy with a few sunny patches, light southeast winds, alpine temperature -5 C, freezing level 1500 m.THURSDAY: Mostly sunny, light southwest winds, alpine temperature -4 C, freezing level 1700 m.FRIDAY: Mostly cloudy, light southwest winds, alpine temperature -4 C, freezing level 1700 m.

Avalanche Summary

On Monday, a large slab avalanche was noted in Duffey Lake Road region in alpine terrain. It was likely triggered by a cornice fall during sunny and warm conditions. The slab likely released on the weak layer described in the Snowpack Summary section. Otherwise, whumphing and cracking were noted at ridgetop, failing 10 to 20 cm deep.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

20 to 40 cm of new snow, with the most near Coquihalla Highway, has been redistributed into lee terrain features from northeast switching to southwest 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 at least 1900 m. 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.The mid and lower snowpack are well-settled and strong.

Problems

Storm Slabs

New snow may not bond well to an underlying crust. Slabs have been most reactive adjacent to ridges in wind-loaded terrain. Watch your overhead exposure, as cornices could trigger slabs on slopes below.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Persistent Slabs

Professionals are travelling cautiously due to a weak layer buried 50 to 100 cm. The layer is found in upper treeline and alpine terrain on shady aspects. Recent avalanches have been reported in the north of the region on this layer.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Loose Wet

The sun packs quite a punch at this time of year. Be cautious if the sun comes out or if you feel warm air temperatures, as this will weaken the snow surface and increase the likelihood of triggering avalanches.

Use extra caution on slopes if the snow is moist or wet.Avoid steep slopes when air temperatures are warm, it is raining, or the solar radiation is strong.Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Valid until: Apr 18th, 2018 2:00PM