Avalanche Forecast

Issued: Jan 26th, 2018 4:45PM

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

jsmith, Avalanche Canada

Sea To Sky.

New snow amounts within this region will be highly variable on Saturday with more snow in the south. Hazard may be one step lower in areas that receive less than 25 cm of new snow.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

SATURDAY: 20-30 cm of new snow / Strong southwesterly ridgetop winds / Freezing level rising to around 1000m.SUNDAY: 20-30 cm of new snow / Strong southwesterly ridgetop winds / Freezing level rapidly rising to around 1800m.SUNDAY NIGHT: 15-25 cm of new snow / Strong southwesterly ridgetop winds / Freezing level around 1800m.MONDAY: 25-30 cm of new snow / Strong to extreme southwesterly ridgetop winds / Freezing level around 1800m.

Avalanche Summary

Throughout this region there has been evidence of a natural avalanche cycle up to size 3 that occurred within the storm snow on Wednesday. More notable are the numerous explosive triggered, very large avalanches up to size 3.5 that where reported near Whistler on Thursday. These avalanches started in the storm snow and then stepped down to the early January and even the mid-December crusts which resulted in very large avalanches running full path. They occurred on northwesterly aspects below rocky ridgetops at around 1950 m. Although these layers are over 200 cm beneath the snow surface, a large trigger such as a falling cornice or a smaller human triggered avalanche could very likely "step-down" to these layers resulting in large and destructive avalanches.

Snowpack Summary

15-20 cm of new snow on Thursday morning brings recent storm totals to around 60-80 cm which continues to be redistributed by strong southeasterly winds. Last weekend's storm created dense storm slabs lurking in lee and cross-loaded features. Impressive cornice growth has also been observed on the lee side of ridgetops. 200-250 cm below the surface you'll find a crust that was buried early January and is present at all elevations. Below this there is another crust which was buried in mid-December. Recent explosive control work has triggered storm slab avalanches that have then "stepped-down" to both of these crusts, resulting in very large avalanches running full path. Although these layers are over 200 cm beneath the snow surface, a large trigger such as a falling cornice or a smaller human triggered avalanche could very likely "step-down" to these layers resulting in very large and destructive avalanches.

Problems

Storm Slabs

New snow, strong winds, and rising temperatures will create touchy storm slabs reactive to human triggers.

Be cautious as you transition into wind affected terrain.Be aware of the potential for wide propagations due to the presence of hard windslabs.The new snow will take time to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Cornices

Large amounts of recent new snow and high winds are creating rapid cornice growth.

Falling cornices may trigger large avalanches on the slopes below.Give cornices a wide berth when travelling on or below ridges.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

Large triggers such as a falling cornice or smaller storm slab avalanches may step-down to deeply buried crusts, resulting in large and destructive avalanches running full path.

Be mindful that deep instabilities are still present and have produced recent large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2.5 - 3.5

Valid until: Jan 27th, 2018 2:00PM