Avalanche Forecast

Issued: Mar 31st, 2017 4:46PM

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

cgarritty, Avalanche Canada

South Columbia.

A complex mix of avalanche problems is maintaining elevated danger in the region. The potential for a storm slab or cornice release to trigger a deeper persistent slab remains a real concern for Saturday.

Summary

Confidence

Moderate -

Weather Forecast

Friday night: Scattered flurries bringing up to 5 cm of new snow. Light to moderate southwest winds.Saturday: Cloudy with continuing flurries bringing 5-10 cm of new snow. light to moderate southwest winds. Freezing level to 1900 metres with alpine temperatures around -1.Sunday: Cloudy with sunny periods and isolated flurries with a trace of new snow. Light northwest winds. Freezing level to 1500 metres with alpine temperatures around -6.Monday: A mix of sun and cloud. Light northwest winds. Freezing level to 1700 metres with alpine temperatures around -5.

Avalanche Summary

Reports from Thursday include numerous observations of storm slabs and wind slabs releasing naturally, with natural cornice falls, skier traffic as well as with ski cutting and explosives control as triggers. Sizes ranged from 1-2.5 and crown fractures generally from 30-60 cm in depth. Northeast to northwest aspects were the most active.On Wednesday, storm slabs proved reactive and ran naturally up to Size 2.5 with a couple larger Size 3 and 3.5. Storm slabs were also reportedly reactive to skier triggers up to size 1.5 at treeline elevations.

Snowpack Summary

30-50 cm of recent storm snow has accumulated at upper elevations. The new snow is dry up high and moist from 1800 m and below. This now brings 80-120 cm of accumulated snow which overlies a rain crust below 2000 m or a sun crust on solar aspects at higher elevations. New wind slabs are developing on leeward slopes and behind terrain features and large, fragile cornices exist along ridgelines. At higher elevations, the February weak layers are down 150-190 cm and woke up during last week's storm with many avalanches stepping down to them. 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 also stepped down to these layers last week resulting in some very large full depth avalanches. These layers remain a real concern while touchier storm slabs and cornices continue to present the risk of acting as triggers for deeper weaknesses.

Problems

Storm Slabs

New storm snow and wind have formed storm slabs that are likely to remain reactive to human triggering on Saturday. Cornices have also grown large and fragile. These may fail with daytime warming or during stormy periods.

The new snow will require several days to settle and stabilize.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Triggers like 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.

Cornices or smaller slab avalanches could step down to deeper layers resulting 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 rain will 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.

Likelihood

Possible - Likely

Expected Size

1 - 2

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