Avalanche Forecast

Issued: Apr 21st, 2012 4:00PM

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

pgoddard, Avalanche Canada

Sea To Sky.

Expect a spike in avalanche activity with the onset of rain. The timing of forecast rain is somewhat uncertain.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Sunday: Light precipitation in the morning, becoming more persistent by evening. Freezing level around 2300 m. Moderate southerly winds.Monday: Moderate precipitation, perhaps 10-20 mm. Freezing level around 2500 m. Moderate to strong SW winds.

Avalanche Summary

Several size 1-2 avalanches were triggered by people and explosives on Friday following overnight snow and wind. These failed on a crust or within recent storm snow layers. Natural avalanches were also triggered by sunshine on solar aspects, and a size 2 natural slab was observed on a NW aspect in Garibaldi Park.

Snowpack Summary

20 cm of snow which fell on Thursday night was shifted into wind slabs on lee slopes. Around 50 cm of snow now overlies a buried crust, which can act as an easy sliding layer. Solar warming de-stabilized new snow above this crust on Friday and Saturday. A deeper crust layer from late March, buried within the upper 2 m of the snowpack, remains a lingering concern for big avalanches, particularly during times of intense or prolonged snowpack warming. Large cornices threaten slopes. Glide slab releases are a possibility, especially in steep rocky terrain. Forecast rainfall is likely to weaken the snowpack, leading to wet loose and slab avalanches, particularly at low elevations and on north aspects which were not influenced by solar radiation on Friday/Saturday.

Problems

Cornices

Large cornices are looming. These are a hazard in themselves and could trigger avalanches on the slope below.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 5

Loose Wet

Two processes are likely to cause wet loose or slab avalanches this weekend: first, sun and second, rain. Recent new snow is likely to slide easily on a buried crust when weakened by these warming processes, especially in steep terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 6

Wind Slabs

Wind slabs have developed with recent snow and moderate winds, and more may develop with incoming weather. Be alert for these behind ridges and terrain breaks.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Apr 22nd, 2012 9:00AM