I started ski season today, in -25°C. At school we only went skiing when it was -15°C or less. In my opinion it doesn't matter how cold it is. The colder the better for me, actually, because the colder it is the slower you have to ski. Breathing is more difficult in the freezing weather. And my skiing is more about having the means to get to a place for the perfect shot than for getting the exercise..
With this method I've never won the gold medal, but I did find gold everywhere I looked.