Avalanche Forecast

Issued: Apr 7th, 2017 4:50PM

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

cgarritty, Avalanche Canada

South Columbia.

Watch for variable wind loading patterns as you gain elevation and maintain avoidance of overhead hazards like cornices and large avalanche paths. A heavy trigger in the right location still risks triggering a very large and destructive avalanche.

Summary

Confidence

High -

Weather Forecast

Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Monday: Cloudy with sunny periods and isolated flurries with a trace of new snow. Light southeast winds. Freezing level to 1700 metres with alpine temperatures around -3.

Avalanche Summary

Reports from Thursday showed storm slabs releasing from Size 1.5-2 with explosives triggers in the Revelstoke area. Loose wet avalanches were observed running from Size 1.5-2 in steep terrain with ski cutting and explosives. Slab crown fractures ranged from 10-60 cm and north to northeast aspects saw the majority of reported activity.Reports from Wednesday included one observation of a natural Size 2.5 wet slab that was triggered by a smaller loose wet avalanche. Loose wet avalanches were generally observed running to Size 1.5 from steep terrain, both naturally and with skier traffic.Several natural cornice falls up to Size 3.5 were reported on Tuesday in the Monashees and the Selkikrks. Natural cornice and one persistent slab avalanche up to Size 3.5 were reported from the Monashees on Monday. The persistent slab avalanche was triggered by a wind slab in steep terrain on a southwest aspect at 2400 metres. On Sunday natural cornice falls released up to Size 2.5, and one pulled an unsupported slope resulting in a deep slab release.

Snowpack Summary

Roughly 30-40 cm of new snow has formed fresh storm slabs on the surface after Thursday and Friday's snowfall. These new storm slabs developed above a mix of old surfaces that include melt-freeze crusts at treeline and below and on solar aspects in the alpine. In addition to storm slab formation, the new snow has also contributed to fragile new cornice growth. Cornices have been a primary avalanche problem in the past week, with recent reports of cornices falling off naturally with loading from wind, or due to warming from direct sun or daytime heating. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers have recently produced large avalanches with large triggers like cornice falls, and they may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Storm Slabs

The storm slabs that formed over the past few days are likely to remain reactive to human triggering on Saturday. These slabs may be more reactive where they overlie recently buried surface hoar, more likely found on shaded alpine slopes.

Use ridges or ribs to avoid pockets of wind loaded snow.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 3

Cornices

Cornices have grown large and may fall off naturally with solar effect or daytime warming. Cornice falls have recently been responsible for triggering large persistent slab avalanches.

Do not travel on slopes that are exposed to cornices overhead.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Persistent Slabs

A cornice fall or smaller slab avalanche currently has the potential to trigger large, destructive avalanches on deeply buried weak layers. This is more likely to occur in thin or variable snowpack areas at higher elevations.

Recognize and avoid runout zones.Cornices or smaller slab avalanches could step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Apr 8th, 2017 2:00PM