Avalanche Forecast

Issued: Apr 23rd, 2017 3:18PM

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

cgarritty, Avalanche Canada

Sea To Sky.

Warm temperatures and solar exposure will promote reactivity in a range of avalanche problems on Monday.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Monday: A mix of sun and cloud. Light north winds. Freezing level to 1900 metres with alpine temperatures of -1.Tuesday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate south winds. Freezing level to 1700 metres with alpine temperatures of -3.Wednesday: Mainly cloudy with scattered flurries bringing up to 5 cm of new snow. Light west winds. Freezing level to 1500 metres with alpine temperatures of -5.

Avalanche Summary

Reports from Sunday showed ski cutting and explosives control triggering numerous storm slabs from Size 1.5-2 in the Whistler area. Crown depths generally ranged from from 15-20 cm but one result from a wind loaded area featured a fracture of up to 70-80 cm deep.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.

Snowpack Summary

Light snowfall and moderate to strong southerly winds formed fresh storm slabs and 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 isolated large cornice releases have recently demonstrated a capacity for triggering large slab avalanches on underlying slopes.

Problems

Wind Slabs

Recent snowfall formed new storm slabs and wind slabs in the lee of exposed terrain features at higher elevations. These slabs may remain reactive to human triggering on Monday, especially as they experience warming from solar exposure.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Cornices

Where cornices exist, they have become unstable should be avoided. Daytime warming and solar exposure will promote cornice reactivity on Monday.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Loose Wet

Daytime warming and solar exposure will promote loose wet avalanches from steep slopes on Monday. This problem will be greater at higher elevations where more new snow recently accumulated.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Apr 24th, 2017 2:00PM