Avalanche Forecast

Issued: Feb 27th, 2014 8:28AM

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

rbuhler, Avalanche Canada

South Rockies.

We are entering a 'low probability/high consequence' phase with a tricky persistent weak layer. Check out this new blog post on difficult decision making and current conditions.Avoid large, unsupported slopes, especially on north aspects.

Summary

Confidence

Fair

Weather Forecast

A weak system will bring precipitation to the region Thursday night and Friday. Meanwhile, arctic air begins to push into the region on Friday. On Saturday and Sunday, weak disturbance from the south will mix with the cold air and may result in light scattered flurries.Thurs. Night/Friday: Snowfall 5-10cm, treeline temperature around -15C, ridgetop winds 10-20 km/h variableSaturday: A mix of sun and cloud, scattered flurries 0-2cm, treeline temperature around -20C, ridgetop winds 10-20 km/h NESunday: A mix of sun and cloud, scattered flurries 1-5cm, treeline temperature around -20C, ridgetop winds 30-50 km/h SW

Avalanche Summary

On Wednesday, we received reports of several natural size 2.5 avalanches from steeper terrain features on south and west aspects triggered by the sun. Also reported was a size 1 skier-triggered wind slab and three size 1 cornices triggered by explosives near Fernie.

Snowpack Summary

The primary concern remains a persistent slab 80-120 cm thick that sits on a stubborn persistent weak layer consisting of a crust, facets, and/or surface hoar. It continues to show sudden planar shears at the interface and a high degree of sensitivity to human triggers. Wide propagations and remote triggering remain a concern. Check out the South Rockies Blog for a video of a snowpack test on this layer. Variable winds have transported some of the surface snow, building wind slabs on leeward slopes. Large cornices remain a concern along ridge lines and threaten the slopes below. South facing slopes have formed a sun crust on the snow surface. New surface hoar formation up to 4mm and near-surface faceting are also being reported. A weakness at the base of the snowpack may still exist in isolated areas of the region but triggering has become unlikely.

Problems

Persistent Slabs

Expect the deeply buried persistent weak layer to continue to produce large and destructive avalanches. Many slopes are still primed for human triggering and remain a concern on all aspects and elevations.

Use conservative route selection, resist venturing out into complex terrain even if you observe no obvious signs of unstable snow.>Remote triggering is a concern, watch out for adjacent slopes.>Avoid unsupported slopes.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 6

Wind Slabs

Older wind slabs still exist in many lee terrain features but are becoming harder to trigger. Some isolated areas may have thin, touchy wind slabs from more recent wind. Weak cornices also remain a concern in isolated areas.

Extra caution needed around cornices with current conditions.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Feb 28th, 2014 2:00PM