I find that when the weather gets really cold, about 40F or cooler (I'm from Louisiana ), the wind-chill factor on the bike becomes unpleasant. I've been walking daily (interspersed with whatever jogging my ankles will tolerate without spraining).
Am I just a wuss, or is this a reasonable variation with temperature? For those who say that I'm just ultrasensitive to cold, you're probably right, but I also bike all summer at 100F AND 100% humidity. Maybe it balances out?