Avalanche Forecast

Issued: Mar 24th, 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.

grant statham, Parks Canada

Banff Yoho Kootenay.

http://www.pc.gc.ca/apps/scond/Cond_E.asp?oID=23022&oPark=100092We have a Special Avalanche Warning in effect because we do not think the danger rating of MODERATE adequately illustrates the complexity in the snowpack right now. Low probability/high consequence. Easter weekend is here; keep it mellow out there.

Summary

Weather Forecast

After a bit more snow overnight on Thursday (< 5 cm), it looks like a nice long weekend ahead with skies clearing off on Friday afternoon and a mix of sun and clouds for Saturday. Valley bottom temperatures could reach up to +8, while freezing levels will rise to 1800 m during the mid-afternoon. Sunday looks the same, with a mix of sun and clouds.

Snowpack Summary

5-10cm 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, snowpacks below treeline are isothermal

Avalanche Summary

Over the past week there have been large avalanches triggered by cornice failures, explosives and humans. Of note was 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 our region. On warm afternoons, wet snow avalanches are occurring below treeline.

Confidence

Due to the number of field observations

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

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.

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.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Mar 25th, 2016 4:00PM