Avalanche Forecast

Issued: Mar 31st, 2017 4:28PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs, Persistent Slabs and Loose Wet.

cgarritty, Avalanche Canada

Purcells.

Forecast winds and light snowfall will see wind slabs and cornices continue to grow. The potential for one of these to release and trigger a deeper persistent slab remains a real concern for Saturday.

Summary

Confidence

Moderate -

Weather Forecast

Saturday: Mainly cloudy with scattered flurries bringing up to 5 cm of new snow. Light to moderate southwest winds. Freezing level to 1900 metres with alpine temperatures around -1.Sunday: Mainly cloudy with scattered flurries bringing a trace to 5 cm of new snow. Light west winds. Freezing level to 1500 metres with alpine temperatures around -6.Monday: A mix of sun and cloud. Light variable winds. Freezing level to 1700 metres with alpine temperatures around -5.

Avalanche Summary

Reports from Thursday include observations of storm slabs releasing to Size 2.5 with explosives triggers. Explosives triggered cornices reached Size 3. Several slabs and/or cornice releases were noted triggering persistent slabs which then ran to ground. North aspects saw the majority of this activity.On Wednesday, a couple of larger storm slab avalanches were reported. They were explosive controlled size 2 and size 3 from South aspects 1800 m and above. There was also one skier controlled size 1.5 slab avalanche that failed on a crust from a South aspect around 2200 m.

Snowpack Summary

10-30 cm of recent snow has fallen at upper elevations and has buried a sun crust on solar aspects. This brings 40-60 cm of accumulated snow over the past week. This recent snow overlies a widespread crust below 2300 m and higher on solar aspects. Alpine wind has recently been strong, mainly from the southwest, and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large, fragile cornices also exist along ridgelines. At higher elevations, the February crust/facet layer is now down around 130-150 cm and has been reactive with several avalanches recently releasing on it. It is expected to be most reactive in the alpine where the snowpack remains dry. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have stepped down to these layers recently resulting in very large avalanches. These layers remain a real concern while touchier wind slabs, storm slabs and cornices continue to present the risk of acting as a trigger for deeper weaknesses.

Problems

Wind Slabs

Recent southwest winds have redistributed storm snow in exposed terrain at higher elevations, forming wind slabs that are likely to remain reactive on Saturday. Cornices are also large and may become weak with daytime warming or during stormy periods

Use ridges or ribs to avoid pockets of wind loaded snow.Be alert to conditions that change with aspect and elevation.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A cornice fall or smaller slab avalanche could trigger large, destructive avalanches on deeply buried weak layers. There is a low likelihood of triggering but a high consequence if triggered. These avalanches would likely run full path.

If triggered, wind slabs or cornices may step down to deeper layers and result in large avalanches.Avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Warmer temperatures and light rain are likely to deteriorate the lower elevation snowpack on Saturday. This has the potential to initiate loose wet avalanches that may slide easily on a buried crust.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Use extra caution on slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Apr 1st, 2017 2:00PM