Avalanche Forecast

Issued: Apr 11th, 2018 4:24PM

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

swerner, Avalanche Canada

Sea To Sky.

The calm before the storm. Storm slabs are reactive to human triggers in the alpine, especially on northerly (leeward) aspects where deeper slabs exist due to wind loading.

Summary

Confidence

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

Weather Forecast

Thursday: Cloudy with some sunny periods. New snow up to 5 cm and strong southwest wind at ridgetop. Freezing level 1300m.Friday: Stormy. New snow 15-25 cm through the day. Ridgetop winds strong from the South. Saturday: The storm continues bringing another 15-20 cm. Ridgetop winds strong from the southwest. Freezing levels 1400 m.

Avalanche Summary

On Tuesday, limited alpine observations existed due to weather. Above 1900 m skier triggered isolated slabs up to size 1 were easily triggered. At lower elevations small loose wet natural avalanche activity occurred. Avalanche activity will be on the rise with the incoming storm. Its still winter out there!

Snowpack Summary

Warm temperatures and rain have moistened the snow surface on all aspects and at all elevations with new snow accumulations in the alpine up to 15 cm. Reactive storm slabs and wind slabs are building with continued snow and strong southwest winds. Ridgelines are heavily corniced and if they fail they would act as a trigger on the slope below. 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 down. 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 are building at upper elevations. Slabs will be thicker in lee features, as the snow will fall with strong southwest winds. If the sun comes out the new snow will likely become unstable and reactive.

Use caution, especially in lee areas in the alpine and treeline. Winds are forming touchy slabs.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.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - 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

Valid until: Apr 12th, 2018 2:00PM