Avalanche Forecast

Issued: Apr 19th, 2018 4:32PM

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

jmcbride, Avalanche Canada

South Coast Inland.

A buried weak layer in the north of the region remains a concern, as well as pockets of wind slab in high, northerly terrain. Also be wary of sunny slopes and cornices should the sun make an appearance.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Cloudy. Ridge wind light to moderate, southwest. Alpine temperature near -4. Freezing level 1200 m.FRIDAY: Mostly cloudy, flurries beginning overnight. Ridge wind light to moderate, southwest. Alpine temperature near -3. Freezing level 1800 m. SATURDAY: Mix of sun and cloud, light flurries. Accumulation 5-10 cm. Ridge wind moderate to strong, southwest. Alpine temperature near -5. Freezing level 1500 m.SUNDAY: Mostly sunny. Ridge wind light, north. Alpine temperature near -2. Freezing level 1800 m.

Avalanche Summary

Explosive control work in the Duffey Lake area on Wednesday produced a size 3 persistent slab avalanche that propagated over 200 m wide, failing on the late March weak layer. This result was on a west to southwest aspect between 2100-2200 m. Storm slabs up to size 2 were also reactive to explosives near ridge crests and were running far and fast in the recent storm snow.Tuesday there was a report skier's remotely (from a distance) triggering a a size 2 wind slab on a steep east aspect in the Duffey Lake area. Read more details here.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 failed on the late March weak layer. 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 late March surface hoar layer. These propagated widely across the slopes. Many slides in the recent storm snow were also observed, often triggered by cornice failures.

Snowpack Summary

20 to 40 cm of recent snow (highest amounts 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, and crusts on all aspects up to at least 2000 m, and possibly higher on south aspects.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

Persistent Slabs

Professionals are traveling 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 large avalanches have been reported in the north of the region on this layer.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

Recent snow may not bond well to an underlying crust. Slabs have been most reactive in wind-loaded terrain near ridge crest.

Be careful with wind loaded areas, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

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. This will weaken the snow surface and increase the likelihood of triggering loose wet avalanches.

Use extra caution on slopes if the snow is moist or wet.Avoid steep slopes when air temperatures are warm, or solar radiation is strong.Cornices become weak with daytime heating and sun exposure. Be aware of overhead hazard.

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

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Apr 20th, 2018 2:00PM