Avalanche Forecast

Issued: Mar 24th, 2013 10:39AM

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

istorm, Avalanche Canada

South Columbia.

Summary

Confidence

Good

Weather Forecast

Synopsis: Stable pattern under a ridge of high pressure expected to continue. In other words, little change.Overnight and Monday: Dry, light westerly winds, solid overnight freeze (-10 to -15 C) with daytime warming (around -5 in alpine). Monday freezing level rising to near 1300 m but above freezing temperatures likely to go higher on slopes facing the sun.Tuesday: essentially a nearly identical forecast to Monday except a couple of degrees warmer.Wednesday: some high cloud drifting in. Tuesday night may stay warmer limiting the overnight freeze and crust recovery at treeline elevations and lower.

Avalanche Summary

Loose wet solar triggered avalanches reported on southerly aspects. Failing cornices are common. Most didn't trigger additional slab avalanches although a few did, including a size 4 just north of the region (likely involving the March 10 surface hoar/crust interface).A fatal snowmobile triggered size 3 avalanche was reported in the southern Purcell mountains. No details are available at this time.

Snowpack Summary

Moist snow may be found on solar aspects up to about 2200 metres. New melt/freeze crusts are developing due to cold clear nights and strong solar radiation during the day. The recent storm amounts are between 40-80 cms at higher elevations. Strong winds overnight and early Wednesday morning developed thick pockets of wind slab at higher elevations. Cooling temperatures have promoted bonding to the moist snowpack at lower elevations. New cornice growth is reported to be extensive and weak. Expect natural cornice falls that may trigger weak layers that are buried down a metre or more on slopes below. The new storm load may trigger the March 10th weak surface hoar layer.

Problems

Cornices

Recent cornice growth is very large and weakly bonded. Large cornice falls may occur naturally or may be triggered by people travelling near to them.

Do not travel on slopes that are exposed to cornices overhead.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

2 - 6

Storm Slabs

Pockets of windslab from localized wind, including downflowing katabatic wind, could be rider triggered. Periods of strong solar radiation may cause loose moist or wet snow to fall out of very steep terrain.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

The March 10th weak layer of surface hoar is buried down more than a metre in most places. Large loads like cornice falls may trigger this deeply buried weak layer.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Mar 25th, 2013 2:00PM