Prep skis with one layer of CH3. Follow up with layer of LF3. Scrape and brush. Be sure to finish prep with a firm nylon brush. In conditions this cold you want to have a hard, "shiny" base. Use the firm nylon brush thoroughly until shiny.
CH4 and LF4 are also acceptable on race morning, but less easy to apply than the CH3 and LF3.
With conditions so cold, we are not recommending a pure-fluoro wax for this weekend.