Avalanche Forecast

Issued: Mar 26th, 2017 3:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs and Cornices.

cgarritty, Avalanche Canada

Sea To Sky.

The weather has been active and storm slabs have been reactive. Maintain a cautious approach while the storm snow stabilizes.

Summary

Confidence

High -

Weather Forecast

Sunday night: Flurries bringing approximately 5 cm of new snow. Light southwest winds.Monday: Cloudy with flurries bringing approximately 5 cm of new snow. Light south winds. Freezing level to 1400 metres with alpine temperatures of -4.Tuesday: Periods of snow bringing 15-20 cm of new snow. Moderate to strong south winds. Freezing level to 1400 metres with alpine temperatures of -3.Wednesday: Periods of snow bringing approximately 20 cm of new snow. Light southeast winds. Freezing level to 1500 metres with alpine temperatures around -3.

Avalanche Summary

Reports from Friday and Saturday included numerous observations of storm slabs releasing typically to Size 1.5 with ski cutting and explosives control in the Whistler area. One natural Size 2 wind slab was reported on Friday as well as one remotely triggered Size 1.5 cornice. Crown fractures were typically 20-40 cm deep.Reports from Thursday showed explosives control in the Whistler area producing storm slab releases to Size 2. Crown fractures were generally 50-100 cm thick.Looking forward, storm slabs may reactive to human triggering on Monday, especially in more wind affected and/or unsupported terrain. Concern also exists for large triggers like cornices or storm slabs to step down to the mid-March interface or, in more isolated areas of the alpine, the deeper mid-February weak layers.

Snowpack Summary

Stormy weather over the end of last week brought roughly 50 cm of wind affected new snow to the region. At about 2000 metres and below, this new snow lies above a crust (March 22) that formed over last week's storm snow. Beneath this older storm snow, an older rain crust that was buried around March 15 is now about 80-100 cm deep. The mid-February crust/facet layer can still be found at the upper end of treeline and into the alpine. This interface is now generally 125-165 cm deep but may present at the surface or up to 250 cm deep in heavily wind affected terrain. Although there is growing confidence in this layer becoming dormant, continued caution is warranted while our recently formed storm slabs remain triggerable. A big enough storm slab or cornice release in the right location may have the potential to coax this layer or the shallower March 15 crust layer into reacting.

Problems

Storm Slabs

Expect recently formed storm slabs to be thicker and more reactive at higher elevations and in the lee of terrain features that are exposed to the wind. Plenty of recent evidence shows storm slabs reacting to skier triggering.

Be alert to conditions that change with aspect and elevation.Dig down to find and test the storm snow interface before committing to bigger terrain.Be increasingly cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Cornices

The warm, wet, and windy storm has seen cornices grow fat. While they are a hazard in themselves, the danger increases when they have the potential to act as a trigger to storm slabs sitting beneath them.

Extra caution needed around cornices with current conditions.Pay attention to overhead hazards like cornices.Even small cornice falls may trigger larger avalanches.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 27th, 2017 2:00PM