Avalanche Forecast
Issued: Dec 17th, 2020 5:47PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Loose Dry and Deep Persistent Slabs.
Conrad Janzen,
Avalanche control on Mt Stephen and Bosworth Friday night.
Strong winds and incoming snow will increase the potential for avalanches triggered at upper elevations to run full path in steep areas. Minimize overhead hazard for the next few days!
Summary
Weather Forecast
Strong West winds and 10-15 cm of new snow are forecast starting Friday afternoon with similar amounts and wind conditions on Saturday and Sunday. Valley bottom temperatures should stay around -5 with ridge top temperatures around -12 to -15.
Snowpack Summary
Wind slabs forming in the alpine with moderate to strong W winds. 40-60 cm of storm snow at treeline sits over the Dec 13 and Dec 7 layers of sun crust, facets and some surface hoar. The Nov crust/facets exist near the bottom of the snowpack in shallow snowpack areas. Snowpack depths at treeline are between 100-180 cm.
Avalanche Summary
Ski resorts reported small ski-cut and explosive triggered wind slabs and loose dry avalanches up to size 1.5 on Thursday. Weather limited visibility in the alpine and no other natural avalanches were observed or reported. One natural size 2.5 storm snow avalanche was reported off Mt Ogden on Thursday covering ski tracks in the path below.
Confidence
Problems
Wind Slabs
Wind slabs are expected to form at treeline and in the alpine on Friday as the winds increase and more snow arrives. These are likely to start failing naturally and even running down into lower elevations in steep terrain.
- Choose ice climbs that are not exposed to avalanches from above.
- Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Dry
Up to 50 cm of low density storm 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
Expected Size
Deep Persistent Slabs
In thin areas, the Nov 5 crust has facets above and below it and exists up to 2500m on shady aspects and higher on solar aspects. This is not as prevalent in the Little Yoho region but we may see action in these zones over the weekend.
- 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
Expected Size
Valid until: Dec 18th, 2020 4:00PM
