Avalanche Forecast

Issued: Apr 9th, 2018 4:34PM

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

mconlan, Avalanche Canada

Sea To Sky.

Expect changing weather on Tuesday: high freezing levels dropping over the day, intense rain switching to snow, and strong winds. Warming will weaken the snow and new snow will form fresh slabs. Be very cautious with these rapid changes.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

TUESDAY: Cloudy with rain switching to snow, accumulation 20 cm, strong to extreme southwest winds, alpine temperature 0 C dropping to -5 C, freezing level 2600 m dropping to 1300 m over the day.WEDNESDAY: Cloudy with snowfall, accumulation 15 cm, light to moderate south winds, alpine temperature -5 C, freezing level 1300 m.THURSDAY: A mix of sun and cloud, light southwest winds, alpine temperature -6 C, freezing level 1300 m.

Avalanche Summary

On Sunday, storm slab and loose wet avalanches were widespread across the region. They were small to large (size 1 to 2), on all aspects, and at all elevations. They were triggered naturally, by skiers, and by explosives. Cornices were also reactive, which triggered storm slabs on the slopes below.

Snowpack Summary

Warm temperatures have moistened the snow surface on all aspects and at all elevations. The forecasted snow on Tuesday will fall on this. On ridges, cornices are reported to be large and fragile. At lower elevations, recent precipitation fell as rain, so expect moist or wet snow conditions.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 120 cm. This layer is spotty in its distribution but has recently produced large avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.Below this, the snowpack is well-settled and strong.

Problems

Storm Slabs

Storm slabs and loose wet avalanches may be reactive in the morning with warm and rainy weather. New storm slabs will form once the rain switches to snow. Slabs will be thicker in lee features, as the snow will fall with strong southwest winds.

Avoid steep slopes when air temperatures are warm, it is raining, or the solar radiation is strong.Use ridges or ribs to avoid pockets of wind-loaded snow.Avoid overhead exposure, as avalanches may run full-path.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

A weak layer buried 60 to 90 cm is still surprising people and producing large and destructive avalanches. Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.

Avoid steep terrain or areas with a thin or variable snowpack.Be aware of the potential for wide propagation due to the presence of buried weak layers.Pay attention to overhead hazards like cornices, which could trigger persistent slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3.5

Cornices

Cornices are very large and fragile. The morning's warm temperatures and rain may quickly deteriorate their stability. Give them a large berth while on ridges and avoid travelling underneath them, as they may trigger avalanches on slopes below.

Avoid travelling on slopes below cornices.Give cornices a wide berth when travelling on ridges.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Apr 10th, 2018 2:00PM