Got out this morning and, looking at the sunny, clear sky, I opted for the jacket only. Left the sweater at home.
Well... it was 26 degrees out there... A thermometer in full sun was 34... It's a 4 km ride to my office, but was really uncomfortable.
SHould know that "clear" in winter means "freezing", sun or no sun.

 

Watch out for black ice. I've read a few posts here and in other forums about guys going down because they didn't see the ice.

 

You bet.
I'm very, very wary of any dark patch on the road. Actually, the best thing would be not to ride at all in such temps...
In town there's no problem By the time I'm around, usually between 8:20 and 8:40, a gazillion cars have already passed on those roads, but I avoid open country riding. Too risky.