Avalanche Forecast

Issued: Feb 20th, 2017 4:00PM

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

conrad janzen, Parks Canada

Banff Yoho Kootenay.

Great skiing with the fresh snow, but make conservative terrain choices. Natural activity has slowed but the potential to trigger large avalanches is still very real. Conditions will remain this way for some time.

Summary

Weather Forecast

A mix of sun and cloud with a few light flurries are forecast over the next few days. Winds should stay in the light range and temperatures are expected to be in the -3 to -12 range with a slow decrease over the forecast period.

Snowpack Summary

Another 5-10cm overnight with light winds. Isolated soft slab formation near ridge crests in the alpine. Persistent problems remain with the lower half of the snow pack being weak and faceted especially in thin areas or near rocky outcrops. Cooler temperatures have helped to stabilize the snow pack below tree line but it is still very weak.

Avalanche Summary

Two notable events in the last 24hrs. One was a remotely triggered size 3 avalanche near Cirque peak triggered by a large whumph almost 200m away. The second was two large avalanches triggered by explosives in "the Elevator Shaft" at Lake Louise after numerous smaller explosives had been tried in the previous 24hrs. All ran on the weak facets.

Confidence

Due to the number of field observations

Problems

Deep Persistent Slabs

There is a thick slab over a structurally weak snowpack at all elevations. Likely areas of triggering are in thin parts of a slope or rocky outcrops at tree line and above where a failure can propagate to deeper areas and cause large avalanches.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Small isolated new wind slabs are present in the alpine. Winds from several days ago have also created firm wind slabs which are now buried. Probe for these buried hard layers especially near ridge crests and in cross loaded features.

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.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Feb 21st, 2017 4:00PM