Avalanche Forecast

Issued: Jan 27th, 2018 6:04PM

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

conrad janzen, Parks Canada

Banff Yoho Kootenay.

Human triggering and some natural avalanche activity continues to occur on the various weak layers buried in our snowpack. We expect this to increase Sunday night and Monday. Minimize exposure and avoid large avalanche terrain until things improve!

Summary

Weather Forecast

Temps on Sunday will be in the -5 to-10'C range at treeline with some warming late in the day and 5-15 cm of snow, mostly later in the day, with the larger amounts to the West. Sunday night should see a rise in temperatures and increased snowfall into Monday which will likely cause a natural avalanche cycle if the current forecast comes true.

Snowpack Summary

Recent alpine winds have created wind slabs in leeward areas up to 1m thick. 25-55 cm of settled snow from recent storms has formed a soft slab over the three persistent weak layers of surface hoar and facets that lurk in the upper half of the snowpack often giving sudden test results. Jan 16 down 25-45cm; Jan 6 down 35-55cm; and Dec15 down 45-80cm

Avalanche Summary

More evidence of a widespread cycle on persistent weak layers up to size 3 in the last 48hrs was observed. One natural size 2 failed mid-day on the Dec 15 layer in Lipalian 3 near Lake Louise. Close calls continue with a skier triggered size 3 at treeline in Kootenay resulting in a deep burial that turned out OK due to a fast response by the group.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Monday

Problems

Persistent Slabs

There are three weak layers in the upper snowpack: Jan 16, Jan 6, and Dec 15. All are a mix of sun crust, surface hoar and facets depending on your aspect and elevation. Avalanches are occurring on these layers and human triggering is likely.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Use conservative route selection, choose supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 3

Wind Slabs

Recent winds and new snow have formed slabs in leeward areas of alpine and treeline terrain, and caused natural avalanches and small cornice failures. These slabs are starting to bond but can still be triggered and may step down to persistent layers.

Use caution in lee areas. Recent wind loading have created wind slabs.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 28th, 2018 4:00PM