Avalanche Forecast

Issued: Jan 15th, 2019 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

As the inversion starts to clear Wednesday and cooling temperatures are anticipated, low confidence with the deep persistent slab problem remains. Remain conservative with your terrain selection given the weak nature of the basal snowpack.

Summary

Weather Forecast

A cooling trend will begin as the inversion breaks down midday Wednesday. Winds will remain light and West to SW. Temps should drop Wednesday to -10C at 2000m and stay there through Thursday. As clouds build from pacific moisture moving in Thursday, expect trace amounts of snow to bury our current surface hoar, suncrust and wind effected surfaces.

Snowpack Summary

Solar crusts on some steep SE to West slopes at TL. Extensive wind effect in the alpine, less at treeline. In thick snowpack areas, the Dec 10th weak layer of facets is now down 100-150cm with a stronger snowpack below. In thin snowpack areas, there is little separation between Dec 10 and the weak depth hoar/ facets sitting 40 cm above the ground

Avalanche Summary

No field trip today and no reports of avalanches. A size 3 slab failed on the south aspect of Mt Fairview sometime during the weekend during the temperature inversion and clear skies. The crown was 70cm to 1m deep and over 1000m wide. The slide ran up the other side of the valley below Sheol. A good example of the deep persistent slab problem.

Confidence

Problems

Deep Persistent Slabs

The weak facets and depth hoar just above the ground have an significant 50-140cm thick slab sitting above them. This slab has been hardened by wind effect TL and above. Some large natural avalanches are still occurring and human triggering is likely

Be aware of the potential for full depth avalanches due to deeply buried weak layers.Be aware of the potential for wide propagations which could result in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Wind Slabs

These wind slabs are becoming older and are likely less reactive but should be treated with respect especially while the warm conditions continue. If initiated these slabs could provide enough load to trigger the deeper basal layers.

Use caution in lee and cross-loaded terrain near ridge crests.

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

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Jan 16th, 2019 4:00PM