Speaking from experience: Just because the sun is out does NOT mean it warms up. I've actually seen it go from -25 in the morning to -38 in mid afternoon. - Not counting the windchill.
People keep asking me if I'm used to the winters. . . You don't get used to the winters, you just adapt. You get a car with a remote starter, you stay inside as much as possible, and you put on LAYERS.