Avalanche Forecast

Issued: Mar 24th, 2017 5:03PM

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

Ruari Macfarlane, Parks Canada

Waterton Lakes.

Low hazard Below Treeline does not mean you can't be hit by a Large avalanche that started higher up. Minimize time in avalanche runout zones (these cross many Waterton trails). While not likely, any natural avalanches may reach runouts.

Summary

Weather Forecast

Saturday: Snowfall overnight, and in squalls throughout the day(5-15cm forecast). Ridge winds: Strong-Extreme SW. Freezing Level at valley floor. Treeline high -4.Sunday: Sun & cloud. W winds becoming light. Freezing Level at valley floor. Treeline Low -8, High -4.Monday: Mainly cloudy, flurries possible. Light winds. Treeline High -2.5

Snowpack Summary

A thick crust overlies a Moist snowpack Below Treeline. Wind exposed terrain is scoured and slick, but pockets of Wind Slab 5-30cm deep sit in sheltered lee terrain. These will grow with snow and wind forecast. A crust from Mid Feb, down 1m, is giving some sudden results in tests. The bottom of the snowpack is faceted, and still weak in places.

Avalanche Summary

On Friday, a small cornice fell into a steep lee slope at treeline. This triggered a relatively deep slab in the steep, rocky slope, which stepped down multiple times to deeply buried Persistent Weak Layers, and to Ground lower down. This ended up as a Large (Size 2.5) avalanche. No new avalanches were observed on Thursday with good visibility.

Confidence

Forecast snowfall amounts are uncertain on Saturday

Problems

Deep Persistent Slabs

A crust down 1m (up to Treeline, and higher on solar aspects), and Facets in the bottom 1/3rd of the snowpack, are persisting as weak layers to be respected. These could be triggered by cornice falls, or by human triggered in isolated areas.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Avoid thin, rocky or unsupported slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Wind Slabs

Pockets of Wind Slab can be found in the Alpine and at Treeline. Due to Extreme, gusty winds these may be lower on the slope than you expect. New snow and wind on Friday night will hide the old windslabs, and create reactive new wind slabs.

Be careful with wind loaded pockets Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Mar 27th, 2017 4:00PM