Avalanche Forecast

Issued: Dec 3rd, 2017 4:00PM

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.

ian jackson, Parks Canada

Banff Yoho Kootenay.

Good ski conditions exist in the alpine, but the winds are forecast to pick up on Monday. Watch for fresh windslab formation and isolated avalanches out of extreme terrain running on the Halloween facet layer

Summary

Weather Forecast

A ridge is forming over the forecast region. 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

Above 2500m, 60cm of snow from last week is being blown into soft windslabs in exposed locations. Below 2500m, up to 30 -50 cm of snow lies over the Nov 27th and Nov 23rd crusts. Both of these now overly the Halloween crust/ facet layer that sits 30-50cm above the ground. This lower layer presents as a facet layer above 2500m and as a crust below.

Avalanche Summary

A few size 2's and one size 3 were observed today with good visibility on a flight from Lake Louise to the Wapta . All were in the high alpine (above 2800m) on E/NE aspects in steep, extreme terrain. Most appeared to step down to near ground, likely the Halloween facets. Triggers were wind loading and cornice failures.

Confidence

The weather pattern is stable

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.

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

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 the winds increase from the NW on Monday.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Dec 4th, 2017 4:00PM