Avalanche Forecast

Issued: Mar 20th, 2016 10:52AM

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

ghelgeson, Avalanche Canada

South Columbia.

Watch for fresh storm slab formation at upper elevations and continue to seek out conservative terrain in an effort to avoid tangling with the late February persistent weak layer.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

A weak upper low moves into the region Monday displacing the ridge that was in place over the weekend. With the ridge collapsed, the door is open to a series of fast moving storms interspersed by the odd ridge. SUNDAY NIGHT: Freezing level around 1900 m, 5 to 10 cm of snow above 1900 m, rain below, moderate southwest wind. MONDAY: Freezing level around 1700 m, 1 to 8 cm of snow at and above treeline, light to moderate southwest wind. TUESDAY: Freezing level starting near valley bottom rising to about 1700 m, light variable wind, no significant precipitation. WEDNESDAY: Freezing level starting near valley bottom rising to about 1500 m, 1 to 5 cm of snow possible, light southwest wind.

Avalanche Summary

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

Cornices

Large unstable cornices overhang countless ridge lines and many of these cornices are teetering on the brink of failure. The weight of an approaching rider, a bit of wind or a period of sunshine could easily induce natural collapse.

Do not travel any where near cornices Monday! These behemoth chunks of dense snow remain weak and could collapse at any moment. You don't want to be underneath one when it fails.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 5

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Storm Slabs

Sunday night's storm should produce 5 to 10 cm of new snow accompanied by moderate to strong southwest winds. Watch for fresh slab formation in wind exposed features at and above treeline.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 21st, 2016 2:00PM