Avalanche Forecast

Issued: Apr 8th, 2017 4:21PM

The alpine rating is moderate, 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.

The upper snowpack will gain strength overnight, but watch for breaks in cloud cover to undermine slab and cornice stability on Sunday. Spring sunshine packs a punch.

Summary

Confidence

High -

Weather Forecast

Sunday: Mainly cloudy with scattered flurries and a trace to 5 cm of new snow. Light southwest winds. Freezing level to 1600 metres with alpine temperatures of -5.Monday: Cloudy with sunny periods. Light south winds. Freezing level to 1600 metres with alpine temperatures of -5.Tuesday: A mix of sun and cloud. Light southwest winds. Freezing level to 1700 metres with alpine temperatures of -4.

Avalanche Summary

Reports from Friday showed skier traffic and explosives triggering storm slabs and wind slabs to Size 1.5 in various areas of the region. Crown fractures reached up to 35 cm. Loose wet avalanches were observed running naturally out of steep terrain to Size 1.5 as well.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.Several natural cornice falls up to Size 3.5 were reported on Tuesday in the Monashees and the Selkikrks.

Snowpack Summary

Roughly 30-40 cm of new snow has formed fresh storm slabs on the surface after a series of storms over the end of the week. 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. 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 produced large avalanches with cornice falls and other heavy triggers in late March. They remain a concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Storm Slabs

New snow and variable winds have developed storm slabs and wind slabs at higher elevations. These slabs may remain reactive to human triggering on Sunday and are more likely to react in areas that were exposed to recent strong winds.

Be especially careful with wind loaded pockets near ridge crests and roll-overs.Use ridges or ribs to avoid pockets of wind loaded snow.Be increasingly cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Cornices

Cornices have grown large and may fall off naturally with solar effect or daytime warming. Cornice falls were responsible for triggering a number of large persistent slab avalanches last week.

Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Avoid travel on slopes that are exposed to cornices overhead.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Apr 9th, 2017 2:00PM