Avalanche Forecast

Issued: Feb 28th, 2014 8:33AM

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.

Conditions remain prime for human-triggered avalanches. Check out this great video from the S.R. field team on the tricky persistent weak layer and current avalanche problem. Also see this recent blog post on the difficult decision-making.

Summary

Confidence

Fair

Weather Forecast

An arctic ridge of high pressure should dominate for Saturday resulting in clear, cold conditions. Unsettled conditions are expected for Sunday. The edge of a weak low pressure system from the coast should result in light snowfall on Sunday night/Monday morning but the timing/track/intensity still remains somewhat uncertain.Saturday: Mostly sunny, treeline temperature around -20C, ridgetop wind light NESunday: A mix of sun and cloud, scattered flurries 0-2cm, treeline temperature around -16C, ridgetop wind increasing to 30-50 km/h SE-SW during the daySun. Night/Monday: Cloudy in the morning, clearing during the day, snowfall 1-5cm overnight, treeline temperature around -5C, ridgetop wind 40-60 SW-W

Avalanche Summary

On Thursday, we received reports of several loose, moist avalanches up to size 2. 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 that sits on a stubborn persistent weak layer consisting of a crust, facets, and/or surface hoar. The layer continues to show a high degree of sensitivity to human triggers. Wide propagations and remote triggering remain a concern. In the thinner snowpack areas such as the Crowsnest and northern Elk Valley, the slab is typically 30-60cm thick. In thicker areas such as the Flathead and around Fernie, the slab typically varies in thickness from 70-150cm. Check out the South Rockies Blog for a new video discussing the persistent weak layer and the current avalanche problem. 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 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.

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

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.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 1st, 2014 2:00PM