Avalanche Forecast

Issued: Mar 18th, 2016 4:00PM

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

stephen holeczi, Parks Canada

Banff Yoho Kootenay.

Simplify your terrain choices this weekend. Sunny skies will increase the danger on solar aspects Saturday, and produce large cornice failures on lee aspects. Numerous weak layers in the snowpack are making for complex decision making. SH

Summary

Weather Forecast

A good valley bottom freeze into Sat. but expect freezing levels to quickly reach 2000m with strong solar input as skies will be clear. There will be a temperature inversion to start Sat. (warmer air aloft in the high alpine). Sunday may be even warmer with cloud moving in in the afternoon. Light Westerly winds throughout the weekend.

Snowpack Summary

The snowpack is complex right now. 40-100 cm of new snow sits on crusts on W through E aspects right up to alpine elevations. This has been reactive with explosives in many areas recently. Thinner snowpack areas have prominent facets at or near the base, and large cornices are sitting above many lee slopes.

Avalanche Summary

Avalanche control on Mts. Stephen ad Dennis Friday produced avalanches to size 3. On the same flight numerous large natural avalanches to size 3 were observed. These were 24-48 hours old on NE through N aspects in the alpine, some stepping right to ground or near ground.

Confidence

Freezing levels are uncertain on Saturday

Problems

Loose Wet

Clear skies and high solar input will cause natural avalanches on solar aspects Saturday. These can provide enough mass to trigger persistent and deep persistent weak layers (listed below) causing larger avalanches.

Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.Small avalanches may trigger deeper instabilities.

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

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2

Persistent Slabs

Avalanches on buried suncrusts with facets have been seen on solar aspects within the last few days. Presently there are several crusts buried on S through E aspects, with 40-100 cm overlying them.

Dig down to find and test weak layers before committing to a line.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 3

Deep Persistent Slabs

Deeper facet layers remain weak, especially in thin or rocky areas. Avoid steep or unsupported terrain, and watch for signs of instability such as whumpfing and cracking.

Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Mar 19th, 2016 4:00PM