Avalanche Forecast

Archived

Feb 27th, 2014–Feb 28th, 2014

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

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.

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

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.