Archived

Avalanche Forecast

Apr 20th, 2017–Apr 21st, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Sea To Sky.

Warm temperatures and strong sunshine will combine to promote reactivity in a range of avalanche problems on Friday.

Confidence

Moderate -

Weather Forecast

Friday: A mix of sun and cloud. Light to moderate southeast winds. Freezing level to 2200 metres with alpine temperatures around 0 to +1.Saturday: Cloudy with flurries bringing 5 cm of new snow to higher elevations by evening. Moderate southeast winds. Freezing level dropping to 1700 metres over the day with alpine temperatures around 0 to -2.Sunday: Mainly cloudy with scattered flurries and a trace of new snow. LIght south winds. Freezing level to 1700 metres with alpine temperatures of -4.

Avalanche Summary

Reports from Wednesday include observations of explosives triggered storm slabs reaching Size 1.5 in the Whistler area. Crown depths averaged 20 cm.Very touchy conditions were reported in the Whistler backcountry on Tuesday, with skiers remote-triggering soft slab avalanches, running on the Easter crust. On Monday, a Size 2 avalanche was triggered on a west aspect in the Tantalus range near 2000m. See here for the excellent and informative MIN report.On Sunday, skiers triggered a Size 1.5 slab avalanche in a northwest facing couloir in the alpine near Whistler. See here for their MIN report.

Snowpack Summary

Stormy weather over the beginning of the week has brought about 30-40cm of new snow to the Sea to Sky mountains, with this precipitation falling as rain below about 1400m. Strong southeast winds over the same time period created pockets of reactive wind slab (up to 50 cm thick) in the alpine and exposed features at treeline, in addition to building fragile new cornice growth. A melt-freeze crust (the 'Easter crust') exists below this new snow on south aspects at all elevations. The new snow has begun to show signs of an improving bond with this crust. The mid and lower snowpack are generally well settled and strong.

Avalanche Problems

Wind Slabs

Recent southeast winds redistributed our new snow into thick wind slabs on leeward aspects in the alpine. Strong solar effect will promote the reactivity of these wind slabs on Friday.

Be especially careful with wind loaded pockets near ridge crests and roll-overs.Be increasingly cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2

Cornices

Where cornices exist, they are unstable and should be avoided. Falling cornices are hazard in themselves but they can also trigger large avalanches. Strong solar radiation will be weakening cornices on Friday.

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 - Likely

Expected Size: 2 - 3

Loose Wet

Warm temperatures and strong sunshine will promote loose wet avalanches throughout the day on Friday, especially in steep terrain. Loose wet slides may occur naturally or with a human trigger.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Minimize exposure when solar radiation is strong, especially if snow is moist or wet.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 2