Avalanche Forecast

Issued: Apr 5th, 2017 3:05PM

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.

triley, Avalanche Canada

Cariboos.

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

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight: 5-10 cm of new snow with moderate southerly winds and freezing down to 1200 metres. Thursday: Another 5-10 cm during the day with light-moderate southerly winds and daytime freezing up to 1800 metres. Friday: 3-5 cm of new snow with light southeast winds and daytime freezing levels up to 2000 metres. Broken or scattered cloud in the afternoon. Saturday: Overcast with flurries and light winds as a cooling trend starts to lower freezing levels.

Avalanche Summary

On Tuesday several natural cornice falls up to size 3.5 were reported, and several natural cornice falls were reported on Monday up to size 3.0.

Snowpack Summary

New snow is forecast to develop new storm slabs in the alpine and at treeline. These new storm slabs are developing above a mix of old surfaces, that include melt-freeze crusts on solar aspects in the alpine, and all aspects at treeline. In some areas the new snow may hide some lingering wind slabs that are left from the last stormy period. The biggest problem lately has been large and fragile cornices, that have regularly fallen off naturally with loading from wind, or due to warming from direct sun or daytime heating. 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 deep weak layers have been released with large triggers like cornice falls, and they may be more likely to fail on southerly aspects during periods of strong solar radiation or from heavy loading from storm snow. Expect cornices to experience new fragile growth during the next few stormy days.

Problems

Storm Slabs

New storm slabs are expected to develop due to forecast new snow and wind.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

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.

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.

Elevations: Alpine, Treeline.

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 4

Valid until: Apr 6th, 2017 2:00PM