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Archived

Avalanche Forecast

Dec 16th, 2020–Dec 17th, 2020
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Banff Yoho Kootenay.

We are at a tipping point as far as avalanche danger, and if there is wind in your area Thursday, avalanche activity will increase. Factor this into the terrain you decide to go into.  Really good ski quality for this time of year.

Weather Forecast

Continued light snow Thursday (5-10cm) accompanied by moderate to strong south-westerly winds in the alpine. Valley bottom temperatures around -5 and ridge-top temperatures around -12 to -15. Continued winds increasing to extreme into the weekend including 20-40cm expected in some areas by the end of Sunday.

Snowpack Summary

The dominant issue in the snowpack is the 20-30 cm of low density storm snow and 20-25 cm of loose facets overtop of the Dec 7th layer of sun crust, facets or surface hoar. Continued winds are continuing to create fresh wind slabs in open terrain. Basal facets and crust are present and most pronounced in shallow areas.

Avalanche Summary

Lake Louise and Sunshine ski resorts report small ski-cut and explosive triggered wind slab and loose dry avalanches up to size 1.5. Lots of reports of alpine natural avalanches up to size 2.5 in the last 24 hours. A mix of wind slabs and loose dry avalanches likely triggered anytime the winds picked up. 

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Avalanche Problems

Loose Dry

Up to 40 cm of low density and facetted surface snow is sluffing easily out of steep terrain wherever it is touched by wind. These avalanches are relatively small but running far and picking up mass as they go.

  • Be cautious with gully features.
  • Be careful of loose dry power sluffing in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Very Likely

Expected Size: 1 - 2

Wind Slabs

So far wind slabs have been noted in the alpine, but may extend down into treeline wherever the wind has gotten to the new snow.  Expect these to grow in size and reactivity in the coming few days.

  • Use caution in lee areas. Recent wind loading have created wind slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Very Likely

Expected Size: 1 - 2.5

Deep Persistent Slabs

The Nov 5 crust has facets above and below it, and exists up to 2500m on shady aspects and higher on solar aspects. We have isolated observations of deep slab avalanches since the storm (including today), and is still on our mind in shallow areas.

  • Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.
  • Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 1 - 3