Avalanche Forecast

Issued: Apr 9th, 2017 4:54PM

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

cgarritty, Avalanche Canada

North Columbia.

The new snow is on a steady stabilizing trend, but avalanche hazards will persist the longest in wind affected areas. Watch for solar exposure to rapidly undermine stability.

Summary

Confidence

High -

Weather Forecast

Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Tuesday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1800 metres with alpine temperatures of -3.Wednesday: Cloudy with sunny periods. Light to moderate east winds. Freezing level to 1900 metres with alpine temperatures of -2.

Avalanche Summary

Reports from Saturday showed storm slabs releasing naturally from Size 1.5-2.5 as well as with ski cutting and explosives control. Crown fracture depths ranged from 30-60 cm and the activity was focused at alpine elevations.Reports from Friday showed storm slabs releasing naturally from Size 2-2.5 on north aspects in the Rogers Pass area. Smaller wind slabs (Size 1-1.5) released naturally and with ski cutting on west aspects northeast of Revelstoke. Numerous loose wet releases up to Size 2 occurred over the previous 24 hours.A report from Wednesday detailed a 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.

Snowpack Summary

30-40 cm of new snow blanketed the region after a series of storms over the end of last week. The new snow buried a mix of old surfaces that include melt-freeze crusts at treeline and below and on solar aspects in the alpine. Fragile new cornice growth also occurred along ridgelines over the course of the week. Below the new snow interface, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. 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 and early April. They remain an ongoing concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Wind Slabs

Variable winds over the course of the recent stormy weather developed wind slabs on a wide range of aspects at higher elevations. Touchier slabs are likely to exist in the immediate lee of ridgecrests and wind-exposed terrain features.

Use ridges or ribs to avoid pockets of wind loaded snow.Be especially careful with wind loaded pockets near ridge crests and roll-overs.Keep an eye out for reverse loading created by shifting winds.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

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.

Avoid 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

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 avalanche runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

Valid until: Apr 10th, 2017 2:00PM