Avalanche Forecast

Issued: Apr 4th, 2017 3:00PM

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.

triley, Avalanche Canada

Cariboos.

Cornice falls have been responsible for most of the avalanches reported in the past few days. Wind slabs or cornices may trigger persistent weak layers resulting in large avalanches.

Summary

Confidence

High -

Weather Forecast

Overnight: Cloud developing with moderate-strong southwest winds and freezing down to 1000 metres. Wednesday: Strong southwest winds combined with 3-5 cm of new snow and daytime freezing up to 1700 metres. Thursday: Overcast with moderate south winds and a couple of cm of new snow. Daytime freezing level to 1800 metres. Friday: Another 3-5 cm of new snow with sunny breaks in the afternoon and freezing levels around 2000 metres.

Avalanche Summary

Several natural cornice falls were reported on Monday up to size 3.0.

Snowpack Summary

Last week's stormy weather brought up to 40 cm of snow to upper elevations. This storm snow overlies a rain crust below about 2000 metres and a sun crust on solar aspects at higher elevations. Several other temperature and or solar crusts are likely to exist within the storm snow, mainly at lower elevations and on solar aspects. Moderate to strong southwest winds during and since the snowfall formed wind slabs on leeward slopes and promoted the growth of large, fragile cornices along ridgelines. At higher elevations, the February weak layers are down about 120-150 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases were also reported in late March and these deeply buried weaknesses remain a serious concern as solar radiation and warming temperatures begin to penetrate the snowpack at increasingly higher elevations. Cornices and wind slabs are also weakened by these warming effects and have the potential to trigger deeply buried weak layers if they release.

Problems

Wind Slabs

Southwest winds continue to transport snow into pockets of wind slab. Wind slabs are most likely to be found on shaded aspects in the alpine.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Cornices are large and may fall off naturally with new loading from wind and snow, or from daytime warming with or without obvious solar.

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

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

2 - 3

Persistent Slabs

A cornice fall or smaller slab avalanche could trigger large, destructive avalanches on deeply buried weak layers. The likelihood of this happening will increase as solar warming weakens unstable cornices and wind slabs over the course of the day.

If triggered, wind slabs or cornices may step down to deeper layers resulting in large avalanches.Recognize and avoid runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

Valid until: Apr 5th, 2017 2:00PM