A return to gusty west winds Friday has generated fresh avalanche activity.
These winds, and the associated Pacific System approaching the region, will bring a slow, steady reprieve from the arctic temperatures... but will keep the avalanche hazard elevated through the weekend.
Up to 80 cm of storm snow in the past week, with strong winds that have shifted from east to north through the week and then back to the west Friday have created extensive wind effect and fresh cornice growth in the alpine as well as slabs down into treeline.
If triggered these slabs may step down to the deeper weak layers to create larger avalanches.
Slabs 40-100 cm deep overlie three persistent weak layers formed in January. The majority of the avalanches we have seen have been on sun crusts on steep solar slopes. Facets and isolated surface hoar can be found on the same interface on shaded aspects.
Facets and depth hoar at the bottom of the snowpack provide weak support for the entire snowpack. Incremental snowfall through the first half of February brought the overlying slab to the tipping point and last week's storm pushed the balance into overload. We have continued to see large, destructive avalanches failing on the November facets and running a long distance over the last few days.
With the increase in west winds Friday, fresh avalanche activity was evident in the Banff area.
Lake Louise avalanche control described triggering several small wind slabs with explosives including some hard slabs and thought there was evidence of fresh natural activity in the surrounding backcountry.
One notable avalanche at Bow Summit ran onto the standard traverse track Thursday. See MIN.
Following last weekend's storm, a settled 20-50cm of snow has been redistributed by east, then north and now west winds. Expect extensive wind effect in the alpine and fresh wind slabs in some unusual locations down into the trees.
The upper snowpack been subject to the surface faceting process during the extended cold temperatures this week and is starting to sluff in very steep terrain.
On steep solar slopes, there are crusts in the middle of the snow pack now down 40 to 110cm while facets and isolated surface hoar will be found on these interfaces elsewhere.
The bottom 30- 50cm of the snowpack remains weak and faceted as is providing poor support for the entire snowpack above.
A Pacific system began its approach Friday and was heralded by winds shifting back to the westerly and increasing to the moderate to strong range. Temperatures followed, however overnight alpine temperatures will still drop to -20 to -25C.
Cloud will develop into flurries Saturday with a few cm expected north of Lake Louise as temperatures rise to -10 to-15C in the alpine during the day.
Overnight Saturday, up to 5cm is expected along the divide as the system passes the region. Temperatures should hold in the -10 to -15C range in the alpine.
