Avalanche Forecast

Issued: Apr 16th, 2018 3:57PM

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

mconlan, Avalanche Canada

Sea To Sky.

Watch out for new wind slabs as well as thick, old wind slabs. They have been reactive to natural and human activity. Don't be complacent with the weak layer lurking in our snowpack, as it has produced large avalanches recently.

Summary

Confidence

Moderate -

Weather Forecast

TUESDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light to moderate west winds, alpine temperature -7 C, freezing level 1200 m.WEDNESDAY: A mix of sun and cloud, light southeast winds, alpine temperature -6 C, freezing level 1300 m.THURSDAY: Morning sun and afternoon clouds, light southwest winds, alpine temperature -5 C, freezing level 1400 m.

Avalanche Summary

On Sunday, a large (size 3) persistent slab avalanche was remotely triggered on a north aspect in alpine terrain after substantial air temperature and solar warming over the day. The avalanche likely released on the weak layer described in the Snowpack Summary.Otherwise, loose wet avalanches were easy to initiate in the afternoon with solar warming. Evidence of large slab avalanches was observed, likely occurring early in the weekend.

Snowpack Summary

10 cm of new snow has been redistributed into lee terrain features from strong north to northeast winds. This overlies variable surfaces, including wind slabs at high elevations, a sun crust on south aspects, and a temperature crust on all aspects up to 1900 m. Previous wind slabs are up to 1 m deep from strong south winds. 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. Professionals are treating it seriously and avoiding terrain because of it.Below this, the snowpack is well-settled and strong.

Problems

Wind Slabs

North winds redistributed recent snow, producing wind slabs in lee features. Previous wind slabs from the weekend are 1 m thick from strong south winds. Watch your overhead exposure, as cornices could trigger slabs on slopes below.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Persistent Slabs

Professionals are still travelling cautiously due to a weak layer buried 60 to 140 cm. Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.

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

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Apr 17th, 2018 2:00PM