Avalanche Forecast

Issued: Mar 21st, 2016 9:02AM

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

triley, Avalanche Canada

Cariboos.

If the sun comes out on Tuesday, recent storm snow and cornices may release naturally. Cornice falls may trigger deeply buried weak layers resulting in very large avalanches.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Scattered flurries overnight with light northwest winds and freezing levels down to valley bottoms. On Tuesday, light northwest winds with light precipitation and freezing levels up to 1700 metres during the day. Some chance of periods of broken skies. On Wednesday, expect 3-5 cm of new snow with moderate southwest winds and a good overnight freeze. Cloudy with freezing levels rising to 1500 metres during the day. On Thursday, continued cloudy with moderate-strong westerly winds and 5-10 cm of new snow.

Avalanche Summary

On Sunday we had reports of numerous storm slab avalanches size 1.5 from various aspects, with a couple reaching size 2.0 on north aspects. On Saturday a wind event triggered a size 3 avalanche that started near 2300 m, failing on a steep un-skiable east facing piece of terrain. Over the last week we have received 5 reports of very large (size 3) avalanches on north, east and south aspects between 1700 and 2400 m. Some have failed after being hit with a large chunk of falling cornice, others have released without a large trigger.

Snowpack Summary

Large cornices loom over many ridge lines and many are teetering on the brink of failure. Old wind slabs may remain a problem on high elevation north facing features. The make up of the late February persistent weak layer is an aspect dependant mix of surface hoar, facets and/or a thick crust down around 70 to 100 cm below the snow surface. Large triggers like natural cornice fall and explosive control work continue to initiate avalanches failing on this interface. The recent warm to cool temperatures should give the overlying slab a bit of strength, but it has yet to prove itself trustworthy. Unfortunately there's not much of a reliable pattern telling us what exact aspects are most suspect. As a precautionary measure, we recommend remaining suspicious of steep unsupported features at and above treeline.

Problems

Storm Slabs

New storm snow may not be well bonded to the old surface. If the sun comes out, loose wet snow in motion may trigger storm slabs where they are sitting on a crust.

Avoid freshly wind loaded features.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

The late February weak layer is becoming less sensitive to triggers, but it has not gone away and it continues to produce very large natural avalanches. Continue to seek out conservative terrain as you plan your day in the mountains.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Use conservative route selection, stick to moderate angled terrain with low consequence.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Cornices

Cornices may be large and fragile. Natural cornice falls may trigger deeply buried weak layers on slopes below resulting in very large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 5

Valid until: Mar 22nd, 2016 2:00PM