Base wax - CH4x
Glide wax - CH4x
Fluor top coat - FC6XS block is not recommended in this extreme cold.
Iron in the CH4x using a iron at 155C. It may take 5 or more passes of the iron to melt the wax into the ski. CH4x is very hard. Which is good!
After the ski has cooled, scrape, then brush 2-3 times with the fine steel brush, then the medium bronze brush. Continue brushing with the white nylon brush, then a horsehair or boars hair brush. Finish with the blue polishing brush.
With this extended period of extreme cold, the snow will be slow, 'squeeky' snow.
It is important to use the very hard CH4x wax, ironed in, scraped and brushed out well. The CH4x is even more important to use than a fluor in these conditions.
A dedicated cold grind ski with numerous layers of CH4x ironed in is highly recommended.