Avalanche Forecast

Issued: Apr 17th, 2018 4:01PM

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

mconlan, Avalanche Canada

Sea To Sky.

A warming trend is expected on Wednesday with possible sunny periods. This recipe recently produced large, destructive avalanches on a buried weak layer. Don't be complacent -- these are not typical spring snowpack conditions.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

WEDNESDAY: Mostly cloudy with light snowfall and afternoon clearing, accumulation 1 to 3 cm, light southeast winds, alpine temperature -6 C, freezing level 1400 m.THURSDAY: Mostly sunny, light southwest winds, alpine temperature -5 C, freezing level 1600 m.FRIDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light to moderate southwest winds, alpine temperature -5 C, Freezing level 1500 m.

Avalanche Summary

On Monday, small slabs and loose wet avalanches were triggered by skiers and the sun.Â The slabs were most often in lee terrain features near ridges.On Sunday, a large (size 3) persistent slab avalanche was remotely triggered by a snowmobile on a north aspect in alpine terrain after substantial air temperature and solar warming over the day.Â The avalanche likely released on the weak layer described in the Snowpack Summary.Â Another large avalanche was observed close to Whistler, on a north aspect around 2000 m, with a depth of about 1 m.Â It was suspected to have released during last weekendâ€™s storm followed by sun and likely on the same weak layer.Â Be particularly cautious with this layer on Wednesday, as the sun may periodically shine along with rising freezing levels.

Snowpack Summary

10 cm of new snow has been redistributed from strong north winds followed by southwest winds.Â This overlies variable surfaces, including old wind slabs at high elevations, a sun crust on south aspects, and a temperature crust on all aspects.Â Ridgelines are heavily corniced and if they fail, they could trigger slabs on slopes below.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.Â Professionals are treating it seriously and avoiding terrain because of it.Below this, the snowpack is well-settled and strong.

Problems

Persistent Slabs

Professionals are travelling cautiously due to a weak layer buried 60 to 140 cm. The layer is found in upper treeline and alpine terrain on shady aspects. Recent avalanches were triggered during sunny and warm weather, which may occur Wednesday.

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

Possible

Expected Size

2 - 3.5

Loose Wet

The sun packs quite a punch at this time of year. Be cautious if the sun comes out or if you feel warm air temperatures, as this will weaken the snow surface and increase the likelihood of loose wet avalanches.

Use extra caution on slopes if the snow is moist or wet.Avoid steep slopes when air temperatures are warm, it is raining, or the solar radiation is strong.Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Wind Slabs

Lingering wind slabs exist near ridges. They are found on all aspects due to winds starting from the north and then shifting to the south. Watch your overhead exposure, as cornice falls could trigger slabs on slopes below.

Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.Use ridges or ribs to avoid pockets of wind-loaded snow.Avoid steep slopes when air temperatures are warm or the solar radiation is strong.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 18th, 2018 2:00PM