It's One

I was talking to Sven about Jill's web site for work. When I called, the first question out of his mouth was, "How cold is it there?" I guess being in northern California, midwestern winters are an intriguing thing. I pulled up Dashboard and told him it was one. I have to confess, "one" sounded like the loneliest number when I said that. Of course, its now an hour later, and the temperature has dropped two degrees. I'd just like to know how the temperature can be less than nothing. Has anyone else wondered that?