Avalanche Forecast

Issued: Jan 29th, 2020 4:00PM

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

william lawson, Parks Canada

Banff Yoho Kootenay.

Extreme winds have increased the avalanche activity in the forecast region. As the storm intensifies the avalanche danger will rise.

Summary

Weather Forecast

The first wave of the incoming Westerly flow starts Wednesday afternoon. We will see sustained strong to extreme winds through the forecast region and small inputs of snow (up to 5 cm). On Friday a second Westerly flow will move in. Heavy precipe, extreme wind and and freezing levels to 2000m are forecasted for Saturday.

Snowpack Summary

There is 40-80 cm above the Dec 31 layer of facets, surface hoar and sun crust which produces test results in the hard range. The bottom layer of the snow-pack consists of weak facets and depth hoar, except for in deeper snow-pack areas (over 2m) where the basal facets are not as prominent.

Avalanche Summary

An increase in natural avalanche activity up to size 2.5 was observed Wednesday. This appeared to be a result of the strong to extreme winds starting late in the morning. With forecasted values of 100 kilometer an hour winds continuing through the weekend, we can expect more natural avalanche activity to come.

Confidence

Timing of incoming weather systems is uncertain

Problems

Wind Slabs

Extreme wind values from the SW are loading lee slopes at alpine and tree line elevations. An increase in natural avalanche activity on this problem was observed Wednesday.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

The Dec 31 layer continues to be a concern. The layer can be found 50 to 80cm down showing varied results in snow pack test. With forecasted snow and wind over the next few days we will likely see an increase in avalanche activity on this layer.

Dig down to find and test weak layers before committing to a piece of terrain.
If triggered the persistent slab may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

In the past week we have seen several avalanches initiate or step down to this deep persistent layer of facets, depth hoar and crusts. Be cautious with shallow snowpack areas and avoid thin spots.

Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.
Avoid shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Jan 30th, 2020 4:00PM