Avalanche Forecast

Issued: Mar 25th, 2016 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

http://www.pc.gc.ca/apps/scond/Cond_E.asp?oID=23022&oPark=100092Heads Up! A Special Avalanche Warning is in effect as we do not think the danger rating of MODERATE adequately illustrates the complexity in the snowpack right now. This is a low probability, high consequence period with a highly variable snowpack.

Summary

Weather Forecast

Friday was mainly clear with a few convective flurries and strong solar input warming the snow to at least treeline on solar aspects and freezing levels reaching 2100m. Saturday looks like a carbon copy with a weak ridge approaching the divide late in the day. Expect a crisp freeze Sunday morning but watch for a low to bring light precip midday.

Snowpack Summary

10-30cm of new snow overlies crusts in most locations except shaded terrain above 2000m. Shallow snowpack areas are weak, and we are concerned about facets in the lower snowpack overlain by a stiff slab which produces easy, sudden collapses in tests. In the absence of a clear night forming a surface crust the snowpack below treeline are isothermal

Avalanche Summary

Over the past week there have been large avalanches triggered by cornice failures, explosives and people. Of note, a large human triggered avalanche in K-Country last Sunday involving a thick, hard slab over weak depth hoar. Similar results can be expected in the BYK region. On warm afternoons, wet snow avalanches are occurring treeline and below

Confidence

Problems

Deep Persistent Slabs

Deep facet layers remain very weak, especially in thin or rocky areas. Avoid large open slopes, steep slopes (>30 degrees) and be wary that you can trigger this problem from a long distance away - the slab is stiff and it propagates far.

Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Cornices

Cornices are large, and warm temperatures make them weak. Ensure you give them a wide berth on ridge crests, as they can pull back a long way when they fail and may trigger avalanches below. If you need to travel under cornices - move quickly.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 3

Loose Wet

This problem should only exist in the afternoon near the valley bottom elevations (below 1500m), and will start once the day has warmed up and the snow at low elevations turns to slush. Ice climbers should avoid low elevation gullies.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Mar 26th, 2016 4:00PM