Avalanche Forecast

Issued: Apr 7th, 2017 4:49PM

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

North 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 1700 metres with alpine temperatures of -4.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Light south winds. Freezing level to 1800 metres with alpine temperatures of -3.Monday: A mix of sun and cloud. Light southeast winds. Freezing level to 1800 metres with alpine temperatures of -3.

Avalanche Summary

Reports from Thursday included observations of two storm slab releases, Sizes 1 and 2.5. The smaller of these was skier triggered and the larger ran naturally. They both occurred on north aspects at 2200 metres and above. Loose wet avalanches were observed running naturally and with ski cutting from Size 1-2.5 in various areas in the region.Reports from Wednesday included details of one natural Size 3.5 deep persistent slab release that occurred on a northeast aspect in the alpine, just northeast of Revelstoke. It was triggered by a smaller storm slab that released above it due to solar warming. One other loose wet avalanche was observed running naturally to Size 2. Low overcast skies were noted obscuring visibility over the day.Natural cornice falls up to size 3.5 continued to be reported on Tuesday.

Snowpack Summary

Roughly 20-40 cm of new snow has formed fresh storm slabs on the surface after Thursday and Friday's snowfall. These new storm slabs have 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 breaking 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

New snow and variable winds have been developing storm slabs at higher elevations. Expect these slabs to remain reactive to human triggering and be aware of the potential for underlying crust or surface hoar interfaces to promote this reactivity.

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.

If triggered, slab avalanches or cornices may step down to deeper layers.Recognize and avoid runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

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