Avalanche Forecast

Issued: Jan 31st, 2018 4:00PM

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

ian jackson, Parks Canada

Banff Yoho Kootenay.

More avalanche control today resulted in many large avalanches, some running to the end of their runouts. Now is a good time to stay out of avalanche terrain!

Summary

Weather Forecast

Continued light precip and winds on Thursday until the next storm arrives on Friday/ Saturday. Temperatures look to remain cool throughout. Precip amounts are greatest on the west of the divide but range from 20-40 cm over the next 3 days. Winds will increase to strong from the west on Friday.

Snowpack Summary

40-80 cm of snow over the last seven days has overloaded 3 persistent weak layers of surface hoar and facets in the upper half of the snowpack: Jan 16 down 30-50cm; Jan 6 down 40-70cm; and Dec15 down 50-100cm. A major avalanche cycle is ongoing with avalanches running fall path on these layers and some stepping down even deeper.

Avalanche Summary

Natural activity has tapered slightly, but big results with explosives proves that these layers are prime for triggering. Results up to size 3.5 again today with deep fractures and wide propagations. Avalanches were triggered by 95% or more of the shots. Some avalanches ran full path and put dust or debris on roads

Confidence

Due to the number of field observations

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 almost certain.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Avoid all avalanche terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 3.5

Wind Slabs

Recent winds and new snow have formed slabs in leeward areas of alpine and treeline terrain, and caused natural avalanches. The slabs are plump and ripe for triggering, and will likely step down to persistent weak layers.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid all avalanche terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Valid until: Feb 1st, 2018 4:00PM