Avalanche Forecast

Issued: Apr 22nd, 2017 3:31PM

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

cgarritty, Avalanche Canada

Sea To Sky.

Winter hasn't fully loosened its grip at higher elevations. Conditions remain dynamic as yet another storm rolls through the region.

Summary

Confidence

Moderate -

Weather Forecast

Saturday night: Flurries bringing up to 10 cm of new snow. Moderate to strong southwest winds.Sunday: Cloudy with continuing flurries bringing a trace to 5 cm of new snow . Light south winds. Freezing level to 1600 metres with alpine temperatures of -3.Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light east winds. Freezing level to 1800 metres with alpine temperatures of -2.Tuesday: Cloudy with flurries bringing approximately 5 cm of new snow. Light to moderate south winds. Freezing level to 1700 metres with alpine temperatures of -3.

Avalanche Summary

Reports from Friday showed significant cornice activity in the Whistler area, with several natural Size 2 releases and one Size 3.5 that triggered a large slab avalanche with a roughly 2 metre deep crown fracture. One of the Size 2 releases also triggered a 100 cm deep slab. Other natural and explosives triggered cornices ranged from Size 2-3 and mainly entrained loose snow, but a few thinner slabs were also triggered.Reports from Thursday included observations of several explosives controlled cornice releases in the Whistler area. Sizes ranged from 1.5 to 2.5 and one release successfully triggered a 15-30 cm by 15 m slab below it. Wednesday's reports showed explosives triggered storm slabs reaching Size 1.5 in the Whistler area. Crown depths averaged 20 cm.

Snowpack Summary

Light snowfall will combine with moderate to strong southerly winds to form fresh wind slabs on the surface at higher elevations over Saturday night. Below the new snow, warm temperatures and sunshine recently moistened surface snow on most aspects and elevations. New snow will form a variable bond with this surface, with a weaker bond expected at higher elevations and northerly aspects where a crust may have formed in advance of new snow accumulations. The mid and lower snowpack are generally well settled and strong, however large cornice releases have recently demonstrated a capacity for triggering large slab avalanches on underlying slopes.

Problems

Wind Slabs

Fresh wind slabs will form over Saturday night as another storm rolls through bringing light snowfall with moderate to strong southwest winds. Slab thickness and reactivity is likely to increase with elevation.

Be careful with wind loaded pockets near ridge crests and roll-overs.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Cornices

Where cornices exist, they have become unstable should be avoided. Cornices will gain fragile new growth with Saturday night's snowfall.

Be aware that cornice releases have potential to trigger deep slabs.Avoid traveling on slopes that are exposed to cornices overhead.Stay well to the windward side of corniced ridges.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Loose Wet

Moist new snow at lower elevations will have the tendency to sluff from steep slopes as daytime temperatures rise on Sunday. This may occur naturally or with a human trigger.

Be cautious of sluffing in steep terrain.Use extra caution on slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Apr 23rd, 2017 2:00PM