Avalanche Forecast

Issued: Apr 4th, 2017 3:08PM

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

North Columbia.

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

Weather Forecast

Overnight: Overcast with moderate southwest winds and freezing down to 800 metres. Wednesday: Strong southwest winds combined with 3-5 cm of new snow and daytime freezing up to 1500 metres. Thursday: Overcast with light southeast winds and a couple more cm of new snow. Daytime freezing up to 1700 metres. Friday: Mostly cloudy with some sunny breaks and periods of convective flurries. Daytime freezing up to 2000 metres.

Avalanche Summary

Natural storm slab avalanches up to size 2.5 were reported on Monday from the Selkirks. Natural storm slab avalanches up to size 3.0 were reported on Sunday from both the Monashees and the Selkirks. Natural and explosives controlled cornice falls released up to size 2.5 on their own, and up to size 3.0 where they pulled a slab on the slope below.

Snowpack Summary

10-20 cm of recent snow now overlies a crust below about 2200 metres (higher on solar aspects) and moist snow below about 1700 metres. Below the new snow interface, storms over the past week brought 40-60 cm of snow to the region. Several other crusts as well as moist snow are likely to exist within this storm snow, mainly at lower elevations and on solar aspects. Moderate to strong southwest winds during and since the storm formed wind slabs on leeward slopes as well as fragile cornices along ridgelines. 90-130 cm of accumulated snow now overlies a more widespread rain crust below 2000 m and sun crust on solar aspects at higher elevations. At higher elevations, the February weak layers are down 160-200 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.

Problems

Wind Slabs

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

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Cornices

Cornices are large and may fall off naturally with new loading from wind, snow or daytime warming. Cornices in motion may trigger persistent weak layers resulting in large avalanches.

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 storm slabs over the course of the day.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

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