The top end of your scale is about right, 40C is 104F, which I do believe as you, is too damn hot, however, I'd put the -10C into the biting cold category, and -20 is simply too cold to go outside. 0 to -9 is the normal winter day and anything slightly above freezing is mild winter.
That depends entirely on where you live, my friend. Here in Norway, some schoolchildren will happily walk to school in -20C on a daily basis during the winter, where I currently live -10C is pretty cold but yet quite normal and certainly doesn't inhibit daily life. And don't even get me started on these wimpy "snow days" that seem to play such a large part of American children's hopes of getting off school.
I'm suing my lawyer since I lost my last case!
Sadly, that happens more often then one would think.
"Been through Hell? Whaddya bring back for me?" -- A. Brilliant