Avalanche Forecast

Issued: Mar 21st, 2016 9:17AM

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

triley, Avalanche Canada

South Columbia.

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 westerly winds with light precipitation and freezing levels up to 1700 metres during the day with periods of broken skies. On Wednesday, expect 5-10 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 10-15 cm of new snow.

Avalanche Summary

On Sunday we had reports of natural cornice falls up to size 3.0 that triggered persistent slab avalanches on the slopes below, and solar triggered persistent slab avalanches up to size 2.5 in the alpine from slopes steeper than 40 degrees. On Saturday cornice fall produced avalanches to size 3 on north and northeast facing features between 2000 and 2400 m, failing on the late February persistent weak layer. Small natural storm and wind slabs were also reported on northwest, northeast and east facing slopes between 2100 and 2400 m.

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 60 to 110 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

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 very large and fragile. Natural cornice falls may trigger buried persistent weak layers on the slopes below, resulting in very large avalanches.

Do not travel on slopes that are exposed to cornices overhead.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 5

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: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

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