Avalanche Forecast
Regions: Banff Yoho Kootenay.
With incoming snow and variable winds that are expected to increase through Sunday, it will be important to make conservative terrain choices this weekend. The possibility of avalanches on the deep persistent layer should be at front of mind.
Weather Forecast
A low pressure system will cross the region Friday night bringing moderate SW winds to the alpine, 5 to 10 cm of snow and a slight up-tick in alpine temperatures to -12C. The temperatures will drop back to -15C values in the alpine early Saturday as flurries diminish midday. Expect winds to shift east in the AM before diminishing in the PM.
Snowpack Summary
Up to10cm of snow Wednesday gives 40-80cm since February. Wind slabs exist in the alpine. A rain crust up to1900m is now buried by 10-20cm of snow. The Dec 31 layer of facets, surface hoar and sun crust is down 50-100cm. The deep persistent basal layer is ~30cm above the ground and is more developed in shallow snowpack areas.
Avalanche Summary
Skier triggered sz 2.5 in the Lipalian 3 in the Lake Louise backcountry Thursday, no injuries
Explosive work at local ski areas has seen the deep persistent layer fail, up to sz 2, to ground under light loads (1kg explosive = human load).
Last weekend's natural avalanche cycle saw large avalanches up to size 3.5 running to valley bottoms.
Confidence
Intensity of incoming weather systems is uncertain on Friday
Avalanche Problems
Wind Slabs
Wind over the last week has redistributed snow in the alpine creating wind effect and forming slabs. An increase in winds overnight Friday with incoming snow, a wind shift to the east Sunday and strong winds forecast for Sunday will build these slabs
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible - Likely
Expected Size: 1 - 2
Deep Persistent Slabs
High consequence deep releases on the facets and depth hoar at the base of the snowpack remain possible. Dealing with the uncertainty around this layer can be somewhat managed by avoiding large, committing terrain and areas with a thin snowpack.
- Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
- Avoid shallow snowpack areas where triggering is more likely.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2 - 3.5
Persistent Slabs
This layer of surface hoar, facets and crusts is down 50 to 100cm and produces variable results, many in the hard range or no result.
- Dig down to find and test weak layers before committing to a line.
Aspects: All aspects.
Elevations: Treeline.
Likelihood: Possible
Expected Size: 1.5 - 3