Avalanche Forecast

Issued: Dec 2nd, 2017 6:12PM

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

Tim Haggarty, Parks Canada

Banff Yoho Kootenay.

Concern remains for the persistent slabs however natural activity has been limited to soft windslabs in the alpine. A new weather pattern will change the wind direction and affect future windslab development.

Summary

Weather Forecast

The skies will clear Sunday morning and winds have already begun to slack and shift to the NW. The more stable pattern that we are entering into will see temperatures drop to -10 to -15 values at treeline for the 3 day period at least. Watch for wind speeds to increase in to the moderate range for Monday.

Snowpack Summary

Below 2500m up to 50 cm of snow lies over the 1127 crust. Another crust (1123) can be found below this and both of these now overlie the 1031 crust that sits 30 to 50cm above the ground. Soft new windslabs are developing in the alpine where up to 60cm can be found over the 1127 wind effect and the 1031 facet crystals are 40 to 50 cm above ground.

Avalanche Summary

A tour to the Ferris Glacier saw very little recent avalanche activity. One sz 2 natural windslab was seen out of a snowfield between two NE facing cliff bands at around 2700m. This freshly formed slab appeared to be 40 to 50 cm deep and likely was a result of wind driven sluffs spilling over the cliffs above.

Confidence

Due to the number of field observations

Problems

Persistent Slabs

Natural avalanche activity has tapered, but concern remains for human triggering of the weak snow on this layer. Previously, slab avalanches have been triggered above ~ 2400m where the Nov. 23rd crust fades out. Shallow alpine areas warrant caution.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Wind Slabs

Up to 50cm of recent snow is available for transport TL and above. So far only light, gusting moderate, SW winds have created soft slabs and wind effect but watch for this to change as winds shift to the NW Sunday and then increase on Monday.

Use caution in lee areas. Recent wind loading has created wind slabs.Watch for surface cracking and stiffer surface layers of snow. Avoid wind loaded terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Dec 3rd, 2017 4:00PM